University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Electroanalysis

  • Publisher: Wiley
  • FAD Code: ELAN
  • CODEN: ELANEU
  • ISSN: 1040-0397
  • Abbreviation: Electroanalysis
  • DOI Prefix: 10.1002/elan
  • Language: English
  • Comments: Fulltext from 1989 V1

Citations 379

"Flow Injection Analysis Of Chloramphenicol By Using A Disposable Wall-jet Ring Disk Carbon Electrode"
Electroanalysis 2007 Volume 19, Issue 1 Pages 65-70
Chun-Yen Liao 1, Chia-Chen Chang 1, Chyung Ay 2, Jyh-Myng Zen

Abstract: A preanodized screen-printed ring disk carbon electrode was applied to the determination of chloramphenicol (Ph-NO2, CAP) by flow injection analysis (FIA). By setting up the first irreversible reduction reaction of Ph-NO2 to Ph-NHOH at the disk electrode, the following reversible oxidation of hydroxylamine (Ph-NHOH) to the nitroso (Ph-NO) derivative can be monitored/collected at the ring electrode for CAP analysis. The interference from dissolved oxygen and others can thus be avoided by using this approach and precise CAP determination can be easily performed by FIA under aerobic conditions. Preanodization treatment helps to lower the overpotential of the electrochemical reaction of CAP and favors the selective detection in aqueous medium. Under the optimum conditions, ten repetitive determinations at 1 ?M and 10 ?M CAP resulted in relative standard deviations of less than 4%, indicating good reproducibility of the system. A linear calibration range of 0.1-20 ?M with a detection limit of 0.074 ?M (S/N = 3) was obtained. Veterinary pharmaceutics were finally analyzed by this sensor to validate its practical applicability.

"Electrostatic Assembly Of A Redox Catalysis System For Detection Of Glutamate"
Electroanalysis 2006 Volume 18, Issue 24 Pages 2397-2404
Alice C. Harper, Mark R. Anderson

Abstract: Interfacial assemblies capable of determining glutamate by redox catalysis are prepared by electrostatic assembly of alternating layers of ferrocene poly(allylamine) polymer and glutamate oxidase on a gold electrode. Deposition of the polymer was confirmed in cyclic voltammetry measurements by the presence of a surface wave corresponding to the oxidation of the ferrocene group. In the presence of glutamate in the adjacent electrolyte solution, the current increases and approaches a pseudosteady state, consistent with redox catalysis. Electrodes modified with glutamate oxidase had a linear response to glutamate up to 0.0045 M with sensitivity of 20 ?A/cm2 and a limit of detection of 31.4 ?M glutamate. An apparent Michaelis - Menten constant of 0.40( ±0.13) mM for the confined glutamate oxidase was determined for this assembly. When used in flow-injection experiments, glucose oxidase modified electrodes responded to transient zones of glucose; however, the detection limits of the assemblies to the flowing stream were substantially higher than found for measurements on static solutions.

"Design And Performance Of A New Thin-layer Radial-flow Holder For A Quartz Crystal Resonator Of An Electrochemical Quartz Crystal Microbalance"
Electroanalysis 2006 Volume 18, Issue 22 Pages 2168-2173
Agnieszka Kochman, Andrzej Krupka, Jerzy Grissbach, Wodzimierz Kutner, Barbara Gniewiska, Lucjan Nafalski

Abstract: A new compact holder for either 5- or 10-MHz AT-cut quartz crystal resonator of an electrochemical quartz crystal microbalance was designed, fabricated and characterized. The holder is a hydrodynamically controlled thin-layer radial-flow microelectrochemical cell. Its unique feature consists of (i) a micrometer-screw adjustable distance between the movable coaxial assembly of the Ag/Ag+ pseudoreference electrode and the inlet capillary nozzle with respect to the metal-film working electrode of the quartz crystal resonator, and (ii) a U-clamp mountable resonator, easily accessible for change without using any tools. The inlet solution stream is centered axially against the working electrode. The holder performance was tested under different flow conditions. These include hydrodynamic voltammetry measurements on the Fe(CN)64-/Fe(CN)63- couple, i.e., a redox system with no mass transfer across the solution-electrode interface, as well as simultaneous chronoamperometry and chronoelectrogravimetry measurements under flow injection analysis (FIA) conditions on the Ag/Ag+ couple, i.e., a system with electrodeposition of a rigid metallic film. Moreover, simultaneous changes of resonant frequency and dynamic resistance were measured under FIA conditions for a glycerol solution, i.e., an electroinactive viscous medium. For the 30 < Fm < 180 µL min-1 volume flow rate of solution and 50 < d < 250 ?m nozzle-to-resonator distance, the holder operates in a thin-layer radial-flow regime at a fully developed laminar flow. For Fm, = 30 µL min-1 and d= 100 ?m, both mass and charge conversion accompanying silver electrodeposition is appreciably high and close to 35%. Simultaneous measurements of the resonant frequency change and current-potential or current-time transients allowed investigations of electrochemical processes involving mass changes of rigid deposits while those of the frequency change and dynamic resistance change involve changes of viscoelastic properties of medium.

"A Novel Potentiometric Membrane Sensor Based On Aryl Palladium Complex For Selective Determination Of Thiocyanate In The Saliva And Urine Of Cigarette Smokers"
Electroanalysis 2006 Volume 18, Issue 21 Pages 2070-2078
Saad S. M. Hassan*, Wagiha H. Mohmoud, Abdel-Sattar S. Hamad Elgazwy, Nahla M. Badawy

Abstract: A highly selective potentiometric sensor for thiocyanate ion based on the use of a newly synthesized organo-palladium ion exchanger complex dispersed in a plasticized poly(vinyl chloride) membrane is described. The sensor displays a Nernstian response (-57.8 ±0.2 mV decade-1) over a wide linear concentration range of thiocyanate (1.0 x 10^-6 - 1.0 x 10^-1 mol L-1), low detection limit (6.3 x 10 -7 mol L-1), fast response (20 s), stable potential readings ( ±0.4 mV), good reproducibility ( ±0.9%), long term stability (8 weeks), high precision ( ±0.7%) and applicability over a wide pH range (4-10). Negligible interferences are caused by F-, Cl -, I-, Br-, NO3-, NO 2-, CN-, SO42-, S 2O32-, PO43-, citrate, acetate and oxalate ions. Under hydrodynamic mode of operation (FIA), the calibration slope is -51.1 ± 0.1 mV decade-1, the linear response range is 1.0 x 10^-5-1.0 x 10^-1 mol L-1 SCN- and the sample throughput is 40-45 per hour. The sensor is satisfactory used for manual and flow injection potentiometric determination of SCN- in the saliva and urine of cigarette smokers and non smokers. The data agree fairly well with results obtained by the standard spectrophotometric technique. Direct potentiometry and potentiometric titration of SCN- with Ag+ are also monitored with the sensor.

"Preparation And Electrocatalytic Performance Of Functionalized Copper-based Nanoparticles Supported On The Gold Surface"
Electroanalysis 2006 Volume 18, Issue 21 Pages 2055-2060
Haiyan Liu, Xiaodan Su, Xuefei Tian, Zhen Huang, Wenbo Song, Jingzhe Zhao

Abstract: Copper nanoparticles (CuNPs) encapsulated by polymeric stabilizer of polyvinylpyrrolidone (PVP) (noted as PVP-CuNPs) were simply prepared and used to construct an enzymeless glucose sensor on a solid substrate. Sensing and assay performance of the CuNPs-based sensor to glucose were evaluated in detail. Cyclic voltammetry (CV), chronoamperometry (I-t) and flow injection amperometry (FIA) revealed a high sensitivity, excellent stability, and good reproducibility in the glucose determination at +0.45 V, which was 200 mV more negative than those in former reports. A detection limit as low as 1.0 x 10^-8 M (signal-to-noise = 3) and a linear range of 1.0 x 10^-7 M to 5.0 x ;10-3 M were obtained in this study.

"Electroanalytical Approach To Evaluate Antioxidant Capacity In Honeys: Proposal Of An Antioxidant Index"
Electroanalysis 2006 Volume 18, Issue 18 Pages 1821-1826
M&oacute;nica &Aacute;vila, Agust&iacute;n G. Crevill&eacute;n, Mar&iacute;a Cristina Gonz&aacute;lez, Alberto Escarpa, Luc&iacute;a Vela Hortig&uuml;ela, Cristina de Lorenzo Carretero, Rosa Ana P&eacute;rez Mart&iacute;n

Abstract: A novel electrochemical route to estimate the antioxidant capacity in honey samples is proposed just using flow injection analysis. The analytical strategy involved the selective oxidation of polyphenolic compounds using two different target potentials, +0.8 and +0.5 V, at two different pHs. An oxidation current obtained at the fixed potential was used as an analytical guide of the antioxidant activity of the target honeys. Chemometrics (correlation and principal component analysis, PCA) demonstrated the significance of the electrochemical protocol versus the traditional spectrophotometric ones in the evaluation of antioxidant capacity and revealed the role of detection potential as a screening variable. The proposed protocol is very simple and fast. However, the most relevant merit of the electrochemical procedure is its inherent versatility which allows the evaluation of the antioxidant activity under predesigned controlled oxidation conditions. In addition, since intercept was statistically zero, its corresponding antioxidant content using just a calibration factor is proposed thus simplifying the calibration-analysis process. As a result, an electrochemical antioxidant index (EAI) is proposed.

"A PVC/TTF-TCNQ Composite Electrode For Use As A Detector In Flow Injection Analysis"
Electroanalysis 2006 Volume 18, Issue 17 Pages 1727-1729
Manuel Cano, Beatriz Palenzuela, Rafael Rodr&iacute;guez-Amaro

Abstract: A new polyvinyl chloride (PVC)/tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) composite electrode was prepared and tested for electroanalytical performance. Different PVC/TTF-TCNQ - graphite proportions were used in order to obtain the best possible detector for accommodation in a wall-jet electrochemical cell of use in flow injection analysis. A PVC/TTF-TCNQ w/w ratio of 1/10 provided the best results in terms of sensitivity, coefficients of variation and mechanical resistance. The voltammetric and flow-injection amperometric detection responses of the electrode to ascorbic acid (AA) were measured and compared with those of a PVC-graphite electrode. The resulting electrode provided good electrode kinetics with a low background current and a relatively reproducible signal. In addition, the electrode can be readily prepared and its surface readily renewed.

"Determination Of Total Calcium In Plasma By Flow Injection Analysis With Tris(2,2-bipyridyl)ruthenium(II) Electrochemiluminescent Detection"
Electroanalysis 2006 Volume 18, Issue 16 Pages 1584-1589
Lihong Shi, Xiaoqing Liu, Haijuan Li, Guobao Xu

Abstract: We described here a new method for the determination of total calcium in plasma. The method is based on the precipitation of calcium with excess oxalate and the measurement of residual oxalate by flow injection analysis with Ru(bpy)32+ electrochemiluminescent detection. It has the advantages of extremely stable reagent, user-friendly instrument, high selectivity, good analytical recovery, wide dynamic range, and nice correlation with atomic absorption spectroscopy. The calibration plot for calcium is linear over a concentration range from 0.5 mmol L-1 to 4.8 mmol L -1, which is wider than those obtained by most other methods. The analytical recoveries for plasma calcium are 98.4-101.2% with coefficients of variation (CVs) of 1.96-2.52%. The within-day CVs range from 0.76% to 0.95%, and between-day CVs were from 1.12% to 1.46%. The time for each injection is one minute. Because the proposed method can be readily carried out on increasingly popular instruments for Ru(bpy)32+ ECL immunoassays and DNA probe assays, Ru(bpy)32+ ECL method is suitable for routine clinical analysis of calcium.

"Amperometric Glucose Biosensor Based On Rhodium Dioxide-modified Carbon Ink"
Electroanalysis 2006 Volume 18, Issue 15 Pages 1499-1504
Petr Kotzian, Petra Br&aacute;zdilov&aacute;, Soa ezkov&aacute;, Kurt Kalcher, Karel Vytas

Abstract: An amperometric method for the determination of glucose using a screen printed carbon electrode is reported. The electrode material was bulk modified with rhodium dioxide and the enzyme glucose oxidase immobilized in a Nafion-film on the electrode surface and investigated for its ability to serve as a detector of glucose in flow injection analysis. The sensor exhibited a linear increase of the amperometric signal with the concentration of glucose in the range of 1-250 mg L-1 with a detection limit (evaluated as 3?) of 0.2 mg L-1 under optimized flow rate of 0.4 mL min-1 in 0.1 M phosphate buffer (pH7.5) carrier. At the potential applied (-0.2 V vs. Ag/AgCl), interferences from redox species present in the sample matrix were negligible. The biosensor reported here retained its activity for more than 40 injections or 4 months of storage at 6°C. The RSD was determined as 1.8% for a glucose concentration of 25 mg L-1 (n = 5) with a typical response time of about 28 s.

"Solid-state Microelectrodes For Flow-cell Analysis Based On Planar Back-side Contact Transducers"
Electroanalysis 2006 Volume 18, Issue 13-14 Pages 1347-1353
Renata Mamiska, Wojciech Wr&oacute;blewski

Abstract: This paper presents an overview of the studies carried out in the recent years in our laboratory, on the construction of different solid-state microelectrodes for flow-cell analysis. The microelectrodes were based on planar transducers made from a printed circuit board and manufactured as back-side contact structures, which facilitate their mounting in a flow-cell. Performances of the polymeric membrane ion-selective: coated-wire microelectrodes and microsensors with a polyHEMA layer containing internal electrolyte are compared. Conducting polymer - polypyrrole doped with ester of sulfosuccinic acid - was added to the PVC membranes to develop all-solid-state microelectrodes without internal electrolyte solution, exhibiting good potential stability in time. Finally, all-solid-state reference microelectrodes based on back-side contact transducers are prepared and examined. These structures were applied as reference electrodes in flow-cell measurements with potassium-selective planar microelectrodes.

"Electrochemical Sandwich Immunoassay For Vitellogenin By Sequential Injection Analysis Using Antibody Immobilized Magnetic Microbeads"
Electroanalysis 2006 Volume 18, Issue 13-14 Pages 1297-1305
Koji Hirakawa 1, Masaaki Katayama 1, Nobuaki Soh 1, Koji Nakano 1, Hiroki Ohura 2, Sumio Yamasaki 2, Toshihiko Imato 1 *

Abstract: A rapid and sensitive sandwich immunoassay based on a sequential injection analysis (SIA) for the determination of carp vitellogenin (Vg) is described. The SIA system was constructed from a syringe pump, a multiposition valve, a flow-through type immunoreaction cell equipped with a magnet and an amperometric detector. Magnetic microbeads immobilized with an anti-Vg monoclonal antibody (primary antibody) were used as a solid support. The primary antibody was immobilized on magnetic microbeads by coupling the primary antibody with a polylactic acid-layer, which was coated on the surface of the magnetic beads, after activated with N-hydroxysuccinimide. The introduction, trapping and flushing out of the magnetic microbeads in the immunoreaction cell were controlled by the magnet and the flow of the carrier solution. After the primary antibody-immobilized magnetic beads were introduced and trapped in the immunoreaction cell, a Vg sample solution, an alkaline phosphatase (AP)-labeled anti-Vg polyclonal antibody (secondary antibody) solution and a p-aminophenyl phosphate (PAPP) solution were sequentially introduced into the immunoreaction cell based on an SIA programmed sequence. Vg was determined by the electrochemical detection of p-aminophenol (PAP), an enzymatic product of PAPP via the action by AP labeled on the secondary antibody. A solution containing PAP, which was generated in the immunoreaction cell and transiently held in a holding coil, was transported to the amperometric detector and the oxidation current of PAP on a working electrode applied at +0.20 V was measured. A sigmoidal calibration curve was obtained in the concentration range from 1 ppb to 500 ppb in a plot of oxidation current against the logarithm of the Vg concentration. The lower detection limit of the immunoassay was about 2-3 ppb. The time required for an analysis was ~15 min/sample.

"Renaissance Of HF Impedimetry In Application To CE Detection"
Electroanalysis 2006 Volume 18, Issue 13-14 Pages 1282-1288
Frantisek Opekar, Karel Stul&iacute;k

Abstract: Some results obtained at the above department in the field of contactless conductivity detection (CCD) are reviewed, in the framework of the state-of-the-art of the field. Several detection cells have been designed and tested. It has been shown that the performance of systems with planar and semitubular electrodes is fully comparable with that of common cells with tubular electrodes and that these systems have advantages in simpler construction and a greater operational versatility. Important characteristic parameters are discussed, primarily the electrode effective length, the gap between the electrodes and the thickness of the dielectric layer. Possibilities of using thin insulated wire electrodes for CCD detection in flow injection analysis are demonstrated.

"Fast Fourier Continuous Cyclic Voltammetry At Gold Ultramicroelectrode In Flowing Solution For Determination Of Ultra Trace Amounts Of Penicillin G"
Electroanalysis 2006 Volume 18, Issue 10 Pages 947-954
Parviz Norouzi*, Mohammad Reza Ganjali, Taher Alizadeh, Parandis Daneshgar

Abstract: In this work, for the first time a fast continuous cyclic voltammetry was used as a highly sensitive detection method for Penicillin G in a flow-injection system. A special computer-based numerical calculation method (using Fast Fourier Transformation) is introduced here for enhancing the analyte signal and noise reduction. During the measurements, the potential waveform (consists of potential steps for cleaning, stripping and potential ramp) was continuously applied on an Au disk microelectrode (with a radius 12.5 ?m in radius). The stripping time was less than 200 ms. Effects of rest potential, sweep rate, and delay time on the sensitivity of the method were investigated. The limit of detection of the method was 1.0 x 10^-11 M. The detection limit of the method is 660 times lower than the most sensitive reported method. The relative standard deviation of the method at 1.0 x 10^-7 M of Penicillin G was 2.7% for 10 runs.

"FIA Determination Of Paracetamol In Pharmaceutical Drugs By Using Gold Electrodes Modified With A 3-mercaptopropionic Acid Monolayer"
Electroanalysis 2006 Volume 18, Issue 9 Pages 931-934
Valber A. Pedrosa, Denise Lowinsohn, Mauro Bertotti

Abstract: A flow injection analysis (FIA) method for the determination of paracetamol in pharmaceutical drugs using a gold electrode modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid is described. At optimized experimental conditions the dynamic concentration range was 0.15 to 15.0 mg L-1 with a detection limit of 0.2 ?g mL-1 (S/N = 3). The repeatability of current responses for injections of 10 ?mol L -1 paracetamol was evaluated to be 3.2% (n = 30) and the analytical frequency was 180 h-1. The lifetime of the modified electrode was found to be 15 days. The results obtained by using the proposed amperometric method for paracetamol determination in four different drug samples compared well with those found by spectrophotometry.

"A LiMn2O4 Based Electrochemical Scheme For Selective Measurement Of Dopamine"
Electroanalysis 2006 Volume 18, Issue 3 Pages 307-310
Hoang Jyh Leu, Meng Shan Lin*

Abstract: A new cathodic scheme was developed for the determination of dopamine by flow injection analysis (FIA). A mild oxidizing agent, lithium manganese (III, IV) oxide (LiMn2O4), as an upstream modifier can oxidize the dopamine to produce the dopaminequinone, and then the oxidized product is subsequently detected by the downstream detector at -0.1 V (vs. Ag/AgCl). In this work, the significant feature of LiMn2O4 based sensing scheme possesses no interference from other tested biological amines including acetylcholine, epinephrine, glutamate, and histamine. Otherwise, there is no detectable interference from ascorbic acid, but 2% and 1% negligible interferences were found from uric acid and acetaminophen, respectively.

"Automated SIA E-tongue Employing A Voltammetric Biosensor Array For The Simultaneous Determination Of Glucose And Ascorbic Acid"
Electroanalysis 2006 Volume 18, Issue 1 Pages 82-88
A. Gut&eacute;s, A. B. Ib&aacute;&ntilde;ez, M. del Valle *, F. C&eacute;spedes

Abstract: An automated voltammetric electronic tongue has been designed employing a biosensor array formed by three different enzymatic Glucose Oxidase (GOD) electrodes and the Sequential Injection Analysis principle. The system is used for its automated training and operation devised for determining glucose and one of its classical interferents, ascorbic acid. The three enzymatic biosensors contain GOD and different metallic catalysts in order to decrease the working potential and to differentiate the response of primary species and interferents. Linear sweep voltammetry has been the chosen technique for data generation and artificial neural networks have been used as the modeling tool. Different learning algorithms have been tried in order to obtaining the best architecture for the neural network. Glucose has been determined in different fruit juice samples by employing this system, correcting the ascorbic acid contents.

"Novel Biomedical Sensors For Flow Injection Potentiometric Determination Of Creatinine In Human Serum"
Electroanalysis 2005 Volume 17, Issue 24 Pages 2246-2253
Saad S. M. Hassan, Eman M. Elnemma, Ayman H. K. Mohamed

Abstract: Coated-wire (CW) and tubular (Tu) type membrane sensors for creatinine are developed. These consist of creatinine tungstophosphate(CTP), creatinine molybdophosphate (CMP) and creatinine picrolonate (CPC) ion-pair complexes as electroactive materials dispersed in plasticized poly(vinyl chloride) matrix membranes. Electrochemical evaluation of these sensors under static (batch) mode of operation reveals near-Nernstian response with slopes of 62.9, 58.1, and 55.2 mV decade-1 over the concentration range 1 x 10^-2-5.0 x 10^-6, 1 x 10^-2-7.5 x 10^-5, and 1 x 10^-2-3.1 x 10^-5 mol L-1. The lower detection limits are 0.39, 3.49, and 2.20 g mL-1 creatinine with CTP, CMP and CPC membrane based sensors plasticized with o-NPOE, respectively. Tubular and coated wire CTP membrane sensors are incorporated in flow-through cells and used as detectors for flow injection analysis (FIA) of creatinine. The intrinsic characteristics of the detectors under hydrodynamic mode of operation in a low dispersion manifold are determined and compared with data obtained under static mode of operation. With 10^-2 mol L-1 phosphate buffer of pH 4.5 as a carrier solution, the tubular and coated wire CTP detectors exhibit rapid response of 58.9 and 50.7 mV decade-1 over the concentration range 1 x 10^-2-1 x 10^-5 mol L-1 and detection limits of 0.39 g mL-1 and 0.85 g mL-1, respectively. Validation of the assay methods with the proposed sensors by measuring the lower detection limit, range, accuracy, precision, repeatability and between-day-variability reveals good performance characteristics confirming applicability for continuous determination of creatinine. The sensors are used for determining creatinine in human blood serum at an input rate of 40 samples per hour. No interferences are caused by creatine, most common anions, cations and organic species normally present in biological fluids. The results favorably compare with data obtained using the standard spectrophotometric method.

"Amperometric Flow-Injection Determination Of Phenolic Compounds Using A Biosensor With Immobilized Laccase, Peroxidase And Tyrosinase"
Electroanalysis 2005 Volume 17, Issue 23 Pages 2137-2146
Ren&aacute;ta Soln&aacute;*, Petr Skl&aacute;dal

Abstract: A screen-printed four-electrode sensor based on immobilization of laccase (Coriolus hirsutus), peroxidase (horseradish) and tyrosinase (mushroom) in the same array was developed for monitoring of phenols. The enzymes were immobilized onto a self-assembled monolayer (4-mercapto-1-butanol) modified gold surface via covalent attachment by epichlorohydrin coupling. The experimental conditions for simultaneous operation of the three enzymes were optimized based on catechol determination. The sensors were further applied for the amperometric detection of several substituted phenolic compounds, carried out using a single line flow-injection system. Hydrogen peroxide served as co-substrate for peroxidase. The limits of detection for phenols in aqueous solutions were in the micromolar range, one assay was completed in less than 5 min. The preliminary studies showed that the compatibility of the above mentioned enzyme array enabled the multielectrode biosensor to be applied to real samples including industrial wastewaters and surface waters.

"Development Of An Automatic Electrochemical System For Differential Pulse Amperometry And Its Application For Se(IV) Determination"
Electroanalysis 2005 Volume 17, Issue 22 Pages 2084-2089
Fabiano Barbieri Gonzaga, Claudete Fernandes Pereira, Antonio Jos&eacute; Moraes Guarit&aacute;-Santos, Jurandir Rodrigues Souza De

Abstract: This work presents the development of an automatic system for differential pulse amperometry (DPA) with electrochemical deposition. The system consists of a microcomputer, running a home-made software, connected to a commercial potentiostat through a data acquisition board. The system was applied for selenium determination using gold electrode and flow injection analysis (FIA). Analytical curves were obtained in the concentration range of 20 to 400 ?g L-1 for Se(IV), with a calculated detection limit of 6 ?g L -1. The analysis results for fish samples doped with Se(IV) and digested in a microwave oven showed recoveries above 93%.

"Thinly Insulated Wire Cells - A New Device For Sensitive Contactless Conductivity Detection In Flow Analyses"
Electroanalysis 2005 Volume 17, Issue 21 Pages 1924-1930
Zuzana Hoher&aacute;kov&aacute;, Frantiek Opekar*, Karel tul&iacute;k

Abstract: Very simple contactless conductivity cells have been designed, suitable for detection in flow analytical techniques (classical HPLC, FIA, SIA, continuous flow, etc.) in which this detection has so far rarely been used. The cells consist of two wire electrodes covered with a very thin layer (units of m) of an insulating material (the dielectric) and punctured through the walls of a plastic tubing at a close mutual distance (from tenths to units of a mm) and placed either across the tube or along the tube axis, so that the detection occurs within the space limited by the two electrodes. As the thickness of the dielectric layer is substantially smaller than that in common contactless conductivity cells used in CE, the AC current flowing between the electrodes is higher and the measuring sensitivity is enhanced. The principal operational characteristics of these detectors have been tested using KCl solutions and compared with those calculated from a simple theoretical model. It has been shown that this model permits theoretical description of these cell types and reasonable prediction of their behavior. Practical application has been demonstrated on a FIA determination of inorganic carbonate.

"Biosensing Of Aromatic Amines In Reversed Micelles With Self-generation Of Hydrogen Peroxide At Glucose Oxidase-peroxidase Bienzyme Electrodes"
Electroanalysis 2005 Volume 17, Issue 19 Pages 1780-1788
Maria Dolores Morales, Maria Cristina Gonz&aacute;lez, Beatriz Serra, Jinbiao Zhang, &Aacute;ngel Julio Reviejo, Jos&eacute; Manuel Pingarr&oacute;n

Abstract: The amperometric biosensing of aromatic amines using a composite glucose oxidase (GOD)-peroxidase (HRP) biosensor in reversed micelles is reported. Rigid composite pellets of graphite and Teflon, in which GOD and HRP were coimmobilized by simple physical inclusion, were employed for the biosensor design. This design allows the in situ generation of the water 2 needed for the enzyme reaction with the aromatic amines, thus preventing the negative effect that the presence of a high H2O2 concentration in solution has on HRP activity. The H 2O2 in situ generation is performed by oxidation of glucose catalyzed by GOD. The effect of the composition of the reversed micelles, i.e., the nature of the organic solvent used as the continuous phase, the nature and concentration of the surfactant used as emulsifying agent, the aqueous 0.05 mol L-1 phosphate buffer percentage used as the dispersed phase, and the glucose concentration in the aqueous phase, on the biosensor response was evaluated. Reversed micelles formed with ethyl acetate, a 5% of phosphate buffer (pH 7.0) containing 3.0 x 10^-3 mol L-1 glucose, and 0.1 mol L-1 AOT (sodium dioctylsulfosuccinate), were selected as working medium. Well-defined and reproducible amperometric signals at 0.00 V were obtained for p-phenylenediamine, 2-aminophenol, o-phenylenediamine, m-phenylenediamine, 1-naphthylamine, o-toluidine and aniline. The useful lifetime of one single biosensor was of 60 days. The trend in sensitivity observed for the aromatic amines is discussed considering the effect of their structure on the stabilization of the radicals formed in the enzyme reaction which are electrochemically reduced. The behavior of the composite bienzyme electrode was also evaluated in a FI (flow injection) system using reversed micelles as the carrier. The suitability of the composite bienzyme electrode for the analysis of real samples was demonstrated by determining aniline in spiked carrots.

"Electrogenerated Chemiluminescence Of Tris(2,2-bipyridyl)ruthenium(II) Immobilized In Humic Acid-Silica-Poly(vinyl Alcohol) Composite Films"
Electroanalysis 2005 Volume 17, Issue 17 Pages 1517-1522
Shou-Nian Ding, Jing-Juan Xu, Hong-Yuan Chen*

Abstract: In this paper, we report the first attempt to use humic acid (HA) as modifiers to prepare the organic-inorganic hybrid modified glassy carbon electrodes based on HA-silica-PVA (poly(vinyl alcohol)) sol-gel composite. Electroactive species of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)) can easily incorporate into the HA-silica-PVA films to form Ru(bpy) modified electrodes. The amount of Ru(bpy) incorporated in the composite films strongly depends on the amount of HA in the hybrid sol-gel. Electrochemical and electrogenerated chemiluminescence (ECL) of Ru(bpy) immobilized in HA-silica composite films coated on a glassy carbon electrode have been studied with tripropylamine (TPA) as the coreactant. The analytical performance of this modified electrode was evaluated in a flow injection analysis (FIA) system with a homemade flow cell. The as-prepared electrode showed good stability and high sensitivity. The detection limits (S/N=3) were 0.050 mol L-1 for TPA and 0.20 mol L-1 for oxalate, and the linear ranges were from 0.10 mol L-1 to 1.0 mmol L-1 for TPA and from 1.0 mol L-1 to 1.0 mmol L-1 for oxalate, respectively. The resulting electrodes were stable over two months.

"Barrel Plating Rhodium Electrode: Application To Flow Injection Analysis Of Hydrazine"
Electroanalysis 2005 Volume 17, Issue 14 Pages 1245-1250
Jun-Wei Sue, Annamalai Senthil Kumar, Hsieh-Hsun Chung, Jyh-Myng Zen *

Abstract: We introduce here the application of barrel plating technology for mass production of disposable-type electrodes. Easy for mass production, barrel plating rhodium electrode (Rh-BPE) is for the first time demonstrated for analytical application. Hydrazine was chosen as a model analyte to elucidate the electrocatalytic and analytical ability of the Rh-BPE system in pH 7 phosphate buffer solution. Flow injection analysis (FIA) of hydrazine showed a linear calibration range of 25-1000 ppb with a slope and a regression coefficient of 5 nA/ppb and 0.9946, respectively. Twenty-two replicate injections of 25 ppb hydrazine showed a relative standard deviation of 3.17% indicating a detection limit (S/N=3) of 2.5 ppb. The system can be continuously operated for 1 day without any alteration in the FIA signals and is tolerable to the interference of oxalic acid, gelatine, Triton X-100, and albumin for even up to 100 times excess in concentration with respect to 400 ppb hydrazine. Since the fabrication cost of the electrode is cheap, it is thus disposable in nature. Furthermore, barrel plating technique can be extendable to other transition metals for application in many fields of research interest.

"Application Of A New PH-Sensitive Electrode As A Detector In Flow Injection Potentiometry"
Electroanalysis 2005 Volume 17, Issue 12 Pages 1085-1090
Heike Kahlert*, Jens R. P&ouml;rksen, Ibrahim Isildak, M&uuml;berra Andac, Murat Yolcu, J&uuml;rgen Behnert, Fritz Scholz

Abstract: A new pH sensitive detector for flow-through potentiometry was developed on the basis of a graphite/quinhydrone composite electrode. The detector was constructed of two polymethylmethacrylate plates between which a 0.1 mm thick sensitive layer is situated. After drilling a hole through the plates, a ring of the sensitive layer is exposed to the solution stream. A conventional calomel reference electrode was placed downstream following the flow-through sensor. The response behavior in different electrolyte solutions was investigated. The detector shows a Nernstian behavior for injections of hydrochloric acid into a KCl background solution as well as for the steady state response in concentration step experiments using hydrochloric acid and buffer solutions. The response time is sufficiently short for FIA applications (T95 between 3 and 5.4 s). The influences of flow rate and injection volume on the detector signal are discussed.

"Flow Injection Analysis Of Mixtures Of Dopamine, Adrenaline And Ephedrine In Human Biofluids Using Stabilized After Storage In Air Lipid Membranes With A Novel Incorporated Resorcin[4]arene Receptor"
Electroanalysis 2005 Volume 17, Issue 10 Pages 887-894
Dimitrios P. Nikolelis*, Christina G. Siontorou, George Theoharis, Istv&aacute;n Bitter

Abstract: This work describes a technique for the rapid, selective and sensitive electrochemical flow injection analysis of mixtures of the stimulating compounds adrenaline, dopamine, and ephedrine using stabilized after storage in air bilayer lipid membranes (BLMs) with incorporated resorcin[4]arene receptor. Injections of the stimulating compounds were made into flowing streams of a carrier electrolyte solution and a transient current signal, with duration of seconds, reproducibly appeared in less than two min after exposure of the lipid membranes to the compounds. The magnitude of this signal was linearly related to the concentration of the compound, which could be determined at micromolar levels. Repetitive cycles of injection of stimulating compounds have shown no signal degradation during each cycle (30 sequential injections). The time of appearance of the transient response was different for each stimulating compound and increased in the order of adrenaline, dopamine and ephedrine. The difference in time of response has allowed selective detection and analysis of these compounds in mixtures. The investigation of the effect of potent interferences included a wide range of compounds usually found in human biofluids, as well as proteins and lipids. The results showed that only proteins (most common in lipid film based biosensors) pose a problem that can be eliminated by modulation of the carrier solution to flow rates that do not allow adsorption of these compounds in the lipid films. The technique was applied in human urine samples.

"Chronopotentiometric Stripping Analysis Using Gold Electrodes, An Efficient Technique For Mercury Quantification In Natural Waters"
Electroanalysis 2005 Volume 17, Issue 9 Pages 755-761
Marcio Antonio Augelli, Rodrigo Alejandro Abarza Munoz, Eduardo Mathias Richter, Amauri Gouveia Junior, L&uacute;cio Angnes

Abstract: This paper proposes a simple methodology for mercury quantification in natural water by stripping chronopotentiometry at constant current, using gold (film) electrodes constructed from recordable CDs in stationary cell. The proposed method allows the direct measurement of labile mercury in natural waters. To quantify total mercury, a robust and low cost UV irradiation system was developed for the degradation of organic constituents of water. The proposed system presents such advantages as excellent sensitivity, low cost, versatility, and smaller dimensions (portability for on-field applications) when compared with other techniques (ICP, GFAAS, fluorimetry) traditionally utilized for mercury quantification. A large linear region of responses was observed, situated over the range 0.02 -200 ?g L-1. Various experimental parameters were optimized and the system allowed quantifications in natural samples, with detection limit of 8 ng L-1 and excellent reproducibility (RSD of 1.4% for 48 repetitive measurements using a 10 ?g L-1 mercury solution). Different metal ions were evaluated, including copper, as possible interferences on stripping mercury signals. Applications of the new method were demonstrated for the analysis of certified and groundwater samples spiked with a known amount of mercury and for the quantification of methylmercury in synthetic oceanic water, originally utilized for fishes contamination experiment.

"Flow Injection Analysis Of Sulfide Using A Cinder/Tetracyano Nikelate Modified Screen-Printed Electrode"
Electroanalysis 2005 Volume 17, Issue 9 Pages 739-743
Jyh-Myng Zen*, Jen-Lin Chang, Pei-Yan Chen, Reiko Ohara, Kuan-Chang Pan

Abstract: Flow injection analysis (FIA) of sulfide is presented using a screen-printed carbon electrode modified with a cinder/tetracyano nickelate hybrid (designated as cinder/NiTcSPE). Hybridization of NiTc was achieved in iron-enriched industrial waste cinder material through the bimetallic formation of Fe(III)[Ni(II)(CN)4]. The electrocatalytic oxidation of sulfide is mediated by the higher oxidation state of Ni in this hybrid-bimetallic complex. The system shows a detection limit (S/N=3) of 0.06 M and a linear working range up to 1 mM in pH 10, 0.1 M KCl solution. Taking into account the relatively low volatility of the analyte in alkaline conditions, the system is ideally suited for the accurate detection of sulfide. The response of the electrode to sulfide is highly reproducible, thereby offering the potential development of a disposable amperometric sensor for sulfide. Selective detection of sulfide in cigarette smoke is presented in this study as an example of a real sample application.

"An Inexpensive Biosensor For Uric Acid Determination In Human Serum By Flow-Injection Analysis"
Electroanalysis 2005 Volume 17, Issue 8 Pages 701-705
R. F. Dutra, K. A. Moreira, M. I. P. Oliveira, A. N. Ara&uacute;jo, M. C. B. S. Montenegro, J. L. L. Filho, V. L. Silva*

Abstract: An inexpensive and easy to construct miniaturized biosensor is described for the determination of uric acid in biological fluids. The amperometric biosensor was prepared by using a carbon paste electrode prepared with uricase from Arthrobacter globiforms and tetracyanoquinodimethane as electron transfer mediator. When incorporated into a flow-injection system it was enabled to perform 50 measurements/h of uric acid in the analytical range of 1-100 mol L-1 with a relative standard deviation of 0.20% (n=14). The system was applied to human serum samples analysis providing good data correlation with those obtained by the reference spectrophotometric method. A linear relationship AM (mol L-1)=1.02 (±0.05) SP (mol L-1) -0.12 (±0.13) was obtained evidencing the absence of significant error. The constructed biosensor was successfully used for at least four months (250 assays) with only a 13% of decrease in the enzymatic activity.

"Determination Of Amino Acids At A Silver Oxide/Silver Phosphate Electrode And The Analysis Of Structure-Response Relationships"
Electroanalysis 2005 Volume 17, Issue 7 Pages 599-606
James M. DeMott Jr., Edwin G. E. Jahngen

Abstract: When a silver electrode is conditioned in a solution of 0.5 M sodium hydroxide with added sodium phosphate and using a dual pulse (500 mV/750 mV vs. Ag/AgCl), a stable silver(I)/silver(II) oxide surface is formed. It has been previously shown that various moieties react with the silver(II) oxide in a chemical oxidation at the outer surface of the oxide layer. This is then followed by re-oxidation of the silver with the generation of current at approximately 500 mV relative to the silver/silver chloride electrode. Previously we found the need to remove carbon dioxide from the base and condition the electrode in a solution containing phosphate ion in order to provide mechanical stability to the oxide layer. We have previously shown this electrode to be applicable to the detection of a variety of carbohydrates. The applicability of the silver oxide/silver phosphate electrode to the post-chromatographic amperometric detection of amino acids was investigated. Calibration studies of amino acids representative of the various classes demonstrated good sensitivity and linearity in the 1-100 M range. Responses of amino acids were measured using glucose as an external standard, in order to correct for variability of the oxide layer. Relative responses of the amino acids ranged from 3 down to 0.1. Correlation with structure suggested the importance of absorption in determining the rate of oxidation. Comparison of arginine with n-benzoyl-L-arginine ethyl ester indicated that side chains as well as the backbone amino group can be oxidized. A Levitch plot of alanine was shown to be linear from approximately 30 to 300 radians per second spin rate at a scan rate of 50 mV per second. Application to post-chromatographic detection was demonstrated.
Amino Acids Electrode Detector

"Speciation Of Inorganic Arsenic In Waters By Potentiometric Flow Analysis With On-Line Preconcentration"
Electroanalysis 2005 Volume 17, Issue 5-6 Pages 504-511
J. A. Rodr&iacute;guez, E. Barrado*, M. Vega, J. L. F. C. Lima

Abstract: A potentiometric flow system has been developed for the direct determination of arsenic(V) in water samples after on-line pre-concentration in a minicolumn packed with a new adsorbent material selective to As(V). Iron oxyhydroxide embedded in silica gel was synthesized and used simultaneously as adsorbent material in the minicolumn and as selective component in a tubular potentiometric electrode. In the first step, the sample solution is mixed on-line with phosphate buffer of pH 7 and pumped through the minicolumn to adsorb As(V). The insertion of the minicolumn in the mobile section of a homemade injector-commutator allows to relocate the minicolumn to desorb the retained As(V) in the second step. The desorption is maximum in the presence of 0.1 M phosphate of pH 12. Maximum response of the tubular selective membrane is achieved in phosphate buffer of pH 7. On-line oxidation of As(III) to As(V) by iodine (I3-) in the presence of phosphate buffer of pH 7 allows the determination of total As as As(V) and then the speciation of inorganic arsenic, since As(III) can be estimated as the difference between total As and As(V). In the optimized experimental conditions, a linear range of 40-500 g L-1 for As(V), and detection limits of 30.6 and 38.6 g L-1 for As(V) and total As, respectively, were obtained.The flow system has been successfully applied to the determination of inorganic arsenic species in groundwater samples collected in areas affected by arsenic contamination. Relative standard deviation of replicated determinations of As in groundwater samples was always below 5%.

"Pulsed Amperometric Detection Of Histamine At Glassy Carbon Electrodes Modified With Gold Nanoparticles"
Electroanalysis 2005 Volume 17, Issue 4 Pages 289-297
V. Carralero, A. Gonz&aacute;lez-Cort&eacute;s, P. Y&aacute;&ntilde;ez-Sede&ntilde;o, J. M. Pingarr&oacute;n

Abstract: Gold nanocrystal-modified glassy carbon electrodes (nAu-GCE) were prepared and used for the determination of histamine by flow injection and high performance liquid chromatography using pulsed amperometric detection (PAD) as the detection mode. Experimental variables involved in the electrodeposition process of gold from a HAuCl4 solution were optimized. A catalytic enhancement of the histamine voltammetric response was observed at the n Au-GCE when compared with that obtained at a conventional Au disk electrode, as a consequence of the microdispersion of gold nanocrystals on the GC substrate. The morphological and electrochemical characteristics of the nAu-GCE were evaluated by SEM and cyclic voltammetry. PAD using a very simple potential waveform consisting of an anodic potential (+700 mV for 500 ms) and a cathodic potential (-300 mV for 30 ms), was used to avoid the electrode surface fouling when histamine was detected under flowing conditions. Flow injection amperometric responses showed much higher Ip values and signal-to-noise ratios at the nAu-GCE than at a conventional gold disk electrode. A limit of detection of 6 x 10^-7 mol L-1 histamine was obtained. HPLC-PAD at the nAu-GCE was used for the determination of histamine in the presence of other biogenic amines and indole. Histamine was determined in sardine samples spiked at a 50 µg g-1 concentration level, with good results. Furthermore, the chromatographic PAD method was also used for monitoring the formation of histamine during the decomposition process of sardine samples.

"Development Of An Enzymeless/mediatorless Glucose Sensor Using Ruthenium Oxide-Prussian Blue Combinative Analogue"
Electroanalysis 2005 Volume 17, Issue 3 Pages 210-222
Annamalai Senthil Kumar, Pei-Yen Chen, Shu-Hua Chien, Jyh-Myng Zen

Abstract: Presented in this work is the first step towards an enzymeless/ mediatorless glucose sensor. We first observed remarkable electrocatalytic oxidation of glucose using combinative ruthenium oxide (RuOx)-Prussian blue (PB) analogues (designated as mvRuOx-RuCN, mv: mixed valent) at ~1.1 V (vs. Ag/AgCl) in acidic media (pH 2 Na2SO4/H2SO4). Individual RuOx and PB analogs failed to give any such catalytic response. A high ruthenium oxidation state (i.e., oxy/hydroxy-Ru(VII), E° = 1.4 V vs. RHE), normally occurring in strong alkaline conditions at RuOx-based electrodes, was electrogenerated and stabilized (without any conventional disproportionation reaction) in the mvRuOx-RuCN matrix for glucose catalysis. Detail X-ray photoelectron spectroscopic studies can fully support the observation. The catalyst was chemically modified onto a disposable screen-printed carbon electrode and employed for the amperometric detection of glucose via flow injection analysis (FIA). This system has a linear detection range of 0.3-20 mM with a detection limit and sensitivity of 40 µM (S/N = 3) and 6.2 µA/(mM cm2), respectively, for glucose. Further steps towards the elimination of interference and the extendibility to neutral pHs were addressed.

"Fast Mapping Of Gunshot Residues By Batch Injection Analysis With Anodic Stripping Voltammetry Of Lead At The Hanging Mercury Drop Electrode"
Electroanalysis 2005 Volume 17, Issue 2 Pages 105-112
Adriana De Donato, Ivano G. R. Gutz*

Abstract: The forensic analysis of lead in gunshot residues (GSR) sampled on the hands of potential shooters is rendered faster, simpler and less expensive by a new batch injection analysis (BIA) method, based on differential pulse anodic stripping voltammetry (DPASV). A simple J shaped adaptor was designed to direct the flux of the analyte injected with a micropipettor onto the hanging mercury drop electrode of any commercial electrode stand. Sampling methods for GSR were compared and lifting with adhesive tape was elected for field use. The tapes are glued on polyethylene screens and stored in capped vials. Sampling with multiple strips provides coarse mapping of the distribution of lead on the shooter's hands. After a dissolution/extraction step with chloroform/aqueous 0.10 mol L-1 HCl, 100 L of the aqueous phase are injected during 25 s for accumulation of lead on the HMDE at -0.60 V (vs. Ag/AgCl). A detection limit of 20 ng/mL of Pb(II), outreaching for GSR analysis, is reached without oxygen removal, at a frequency of 20 injections per hour. Results for sequences of shootings with a revolver and a pistol are presented.

"Cathodic Electrochemical Detection Of Nitrophenols At A Bismuth Film Electrode For Use In Flow Analysis"
Electroanalysis 2004 Volume 16, Issue 19 Pages 1616-1621
Emily A. Hutton, Bozidar Ogorevc*, Malcolm R. Smyth

Abstract: The bismuth film electrode (BiFE) is presented for use in both batch voltammetric and flow injection (FI) amperometric detection of some nitrophenols (2-nitrophenol, 2-NP; 4-nitrophenol, 4-NP; 2,4-dinitrophenol, 2,4-DNP). The bismuth film was deposited ex situ (batch measurements) and in-line (FI) onto a glassy carbon substrate electrode. Batch analysis of the nitrophenols was carried out in 0.04 M Britton Robinson (BR) buffer pH 4, while for FI measurements, a carrier/electrolyte solution composed of 0.1 M BR buffer pH 4 mixed with methanol (20+80, v/v%) was employed to resemble media used in pre-concentration/clean-up and flow separation sample pretreatment procedures. Under batch conditions, the voltammetric behavior of the nitrophenols was examined for dependence on medium pH in the range of 2 to 10. Employing the square-wave voltammetry mode, the limits of detection were 0.4 g L-1, 1.4 g L-1, and 3.3 g L-1 for 2-NP, 4-NP, and 2,4-DNP, respectively. Under flow conditions, a simple in-line electrochemical bismuth film renewal procedure was tested and shown to provide very good inter- and intra-electrode reproducibility of the current signals at low g L-1 analyte concentrations. The limits of detection for 2-NP, 4-NP and 2,4-DNP obtained using FI and amperometric detection at -1.0 V (vs. Ag/AgCl) were 0.3 g L-1, 0.6 g L-1 and 0.7 g L-1, respectively, with linear ranges extending up to 20 g L-1. The attractive performance of the BiFE under flow analysis conditions offers great promise with respect to its detection capability and to its use for a prolonged period of time with no need for inconvenient removal of the electrode from the system for mechanical surface treatment.

"A Lactulose Bienzyme Biosensor Based On Self-assembled Monolayer Modified Electrodes"
Electroanalysis 2004 Volume 16, Issue 17 Pages 1385-1392
Susana Campuzano, Mar&iacute;a Pedrero, F. Javier Manuel de Villena, Jos&eacute; M. Pingarr&oacute;n

Abstract: A bienzyme biosensor in which the enzymes ?-galactosidase (?-Gal), fructose dehydrogenase (FDH), and the mediator tetrathiafulvalene (TTF) were coimmobilized by cross-linking with glutaraldehyde atop a 3-mercaptopropionic acid (MPA) self-assembled monolayer on a gold disk electrode, is reported. The working conditions selected were Eapp = 0.10 V and (25±1)°C. The useful lifetime of one single TTF-?-Gal-FDH-MPA-AuE was surprisingly long, 81 days. A linear calibration plot was obtained for lactulose over the 3.0 x 10^-5 - 1.0 x 10^-3 mol L-1 concentration range, with a limit of detection of 9.6 x 10^-6 mol L-1. The effect of potential interferents (lactose, glucose, galactose, sucrose, and ascorbic acid) on the biosensor response was evaluated. The behavior of the SAM-based biosensor in flow-injection systems in connection with amperometric detection was tested. The analytical usefulness of the biosensor was evaluated by determining lactulose in a pharmaceutical preparation containing a high lactulose concentration, and in different types of milk. Finally, the analytical characteristics of the TTF-?-Gal-FDH-MPA-AuE are critically compared with those reported for other recent enzymatic determinations of lactulose.

"Dopamine And Glucose Sensors Based On Glassy Carbon Electrodes Modified With Melanic Polymers"
Electroanalysis 2004 Volume 16, Issue 15 Pages 1244-1253
Rosa Gonz&aacute;lez, Alberto S&aacute;nchez, Manuel Chicharro, Mar&iacute;a D. Rubianes, Gustavo A. Rivas

Abstract: This work deals with the study of polymers electrogenerated from different catechols at glassy carbon electrodes and the analytical applications of the resulting modified electrodes for dopamine quantification and glucose biosensing. The electropolymerization was performed from a 3.0 x 10 -3 M catechol solution (catechol, dopamine, norepinephrine, epinephrine or L-dopa in a 0.050 M phosphate buffer pH 7.40) by applying 1.00 V for 60 min. The properties of the polymers are very dependent on the nature of the catechol, L-dopa being the best. Glassy carbon electrodes modified with melanic polymers electrogenerated from L-dopa and norepinephrine were found to be suitable for dopamine determinations in flow systems, although the behavior was highly dependent on the nature of the monomer. Detection limits of 5.0 nM dopamine and interferences of 9.0 and 2.6% for 5.0 x 10^-4 M ascorbic acid and 5.0 x 10^-5 M dopac, respectively, were obtained at the glassy carbon electrode modified with a melanin-type polymer generated from L-dopa (using 1.0 x 10^-3 M AA in the measurement solution). The advantages of using a melanin-type polymer generated from dopamine to improve the selectivity of glucose biosensors based on carbon paste electrodes containing Pt and glucose oxidase (GOx) are also discussed. The resulting bioelectrodes combines the high sensitivity of metallized electrodes with the selectivity given by the polymeric layer. They exhibit excellent performance for glucose with a rapid response (around 10 seconds per sample), a wide linear range (up to 2.5 x 10^-2 M glucose), low detection limits (143 ?M) and a highly reproducible response (R.S.D of 4.9%). The bioelectrodes are highly stable and almost free from the interference of large excess of easily oxidizable compounds found in biological fluids, such as ascorbic acid (AA), uric acid (UA) and acetaminophen.

"Development Of A Tubular Sensor Based On A Polypyrrole-doped Membrane For The Potentiometric Determination Of The Dodecylsulfate Anion In A FIA System"
Electroanalysis 2004 Volume 16, Issue 15 Pages 1236-1243
Giaan Arturo &Aacute;lvarez-Romero, Adriana Morales-P&eacute;rez, Alberto Rojas-Hern&aacute;ndez, Manuel Palomar-Pardav&eacute;, Maria Teresa Ram&iacute;rez-Silva

Abstract: Potentiostatic polymerization of polypyrrole doped with dodecylsulfate anion (DS-) was carried out in situ over a tubular composite (graphite-epoxy resin) support in order to develop a potentiometric DS - sensor (TISE) suitable for flow injection analysis (FIA). The sensibility of the TISE was maximized using the SIMPLEX algorithm in terms of the concentration of the pyrrole monomer, the concentration of DS-, the potential imposed and polymerization time. Response times between 2 and 4 minutes were observed. The analytical parameters obtained with the flow system were compared with those obtained in batch studies. In both, flow and batch analysis, potential vs. DS- concentration curves displayed two linear regions with different slopes. Flow analysis for DS- ion brings a total linear range of 1.58 x 10^-5 M to 3.88 x 10 -3 M with a maximum sensibility of 36.4 mV/concentration decade, meanwhile in batch studies the total linear range found was of 6.31 x 10^-6 M to 1.0 x 10^-3 M with a maximum sensibility of 54.49 mV. The flow system response pH range was from 5 to 8. The reproducibility in terms of the relative error of the mean of different experiments was 1.58%. Two salient features of the system designed and built are worthy of mention: the sensor presented high selectivity to the dodecyl sulfate ion as compared to other inorganic anions including other anionic surfactants. The sensor lifetime in the FIA system by means of the sensibility changes was found to be of approximately four months.

"A Portable Fill-and-Flow Channel Biosensor With An Electrode To Predict The Effect Of Interferences"
Electroanalysis 2004 Volume 16, Issue 15 Pages 1221-1226
Min Zhao, Ian S. Harding, D. Brynn Hibbert*, J. Justin Gooding

Abstract: A portable fill-and-flow channel biosensor with a predictor electrode is described. The predictor electrode, on the opposite channel wall and upstream of the detector electrode, allows direct evaluation of the current due to interfering species at the detector electrode. A model is developed which shows that the reaction at the upstream predictor electrode has no significant effect on the concentration distribution of the interfering species at the detector electrode. This enables a straightforward correction of the current at the detector electrode and a determination of the analyte concentration. The effect of interference from ascorbic acid in the detection of glucose in samples was efficiently removed by using such a concept. The recovery of glucose from samples containing ascorbic acid was 103% (s=12%, n=3). The approach was also applied to a biosensor for the determination of glucose in red wine samples containing polyphenolic interferents.
Glucose

"3-Indoxyl Phosphate As An Electrochemical Substrate For Horseradish Peroxidase"
Electroanalysis 2004 Volume 16, Issue 12 Pages 988-993
Pablo Fanjul-Bolado, Mar&iacute;a Bego&ntilde;a Gonz&aacute;lez-Garc&iacute;a, Agust&iacute;n Costa-Garc&iacute;a

Abstract: In this work 3-indoxyl phosphate (3-IP), an alkaline phosphatase substrate, is demonstrated to be a suitable substrate for horseradish peroxidase (HRP). HRP catalyzes the oxidation of 3-IP in presence of hydrogen peroxide (H 2O2) generating the product indigo blue, which is an aromatic heterocycle compound insoluble in aqueous solutions. This product was easily converted into its soluble parent compound indigo carmine (IC) (by addition of fuming sulfuric acid to the reaction media) which has a reversible voltammetric peak at the formal potential of - 0.15 V (vs. Ag pseudo-reference electrode) when a screen-printed carbon electrode (SPCE) is used. Parameters that influence the enzymatic reaction, such as pH, temperature, substrate concentration and reaction time have been optimized. Moreover, the enzyme apparent kinetic constants (Vmax, KM) for both substrates (3-IP and H2O2) have been calculated. Indirect measurements of HRP activity in solution were carried out not only by cyclic voltammetry but also using amperometric detection in a flow system. The detection limits were 6.86 x 10^-12 and 5.68 x 10 -12 M, respectively. Thus, 3-IP is the first substrate that could be used for alkaline phosphatase (AP) and HRP, the most common enzymatic labels in affinity assays.

"Study Of The Electrochemical Behavior Of Disperse Blue 1-modified Graphite Electrodes. Application To The Flow Determination Of NADH"
Electroanalysis 2004 Volume 16, Issue 11 Pages 949-954
Dimitrios V. Stergiou, Mamas I. Prodromidis, Panayotis G. Veltsistas*, Nikolaos P. Evmiridis

Abstract: The preparation and the electrochemical study of Disperse Blue 1-chemically modified electrodes (DB1-CME), as well as their efficiency for the electrocatalytic oxidation of NADH is described. The proposed mediator was immobilized by physical adsorption onto graphite electrodes. The electrochemical behavior of DB1-CME was studied with cyclic voltammetry. The electrochemical redox reaction of DB1 was found to be reversible, revealing two well-shaped pair of peaks with formal potentials 152 and -42 mV, respectively, (vs. Ag/AgCl/3 M KCl) at pH 6.5. The current Ip has a linear relationship with the scan rate up to 800 mV s-1, which is indicative for a fast electron transfer kinetics. The dissociation constants of the immobilized DB1 redox couple were calculated pK1 = 4 and pK2 = 5. The electrochemical rate constants of the immobilized DB1 were calculated k1° = 18 s-1 and k2° = 23 s-1 (? = 2.36 nmol cm-2). The modified electrodes were mounted in a flow injection manifold, poised at + 150 mV (vs. Ag/AgCl/3 M KCl) and a catalytic current due to the oxidation of NADH was measured. The reproducibility was 1.4% RSD (n = 11 for 30 ?M NADH) The behavior of the sensor towards different reducing compounds was investigated. The sensor exhibited good operational and storage stability.

"Flow-Injection Amperometric Detection With Solvent Polymeric Membrane Ion Sensors"
Electroanalysis 2004 Volume 16, Issue 10 Pages 827-831
Joaqu&iacute;n A. Ortu&ntilde;o, Jorge Hern&aacute;ndez, Concepci&oacute;n S&aacute;nchez-Pedre&ntilde;o*

Abstract: An amperometric detector for hydrophobic ions based on a plasticized poly(vinyl) chloride (PVC) membrane incorporated in a flow-injection system was developed. A four-electrode potentiostat with ohmic drop compensation was used, while a flow-through cell incorporated the four electrodes and the membrane, which contained tetrabutylammonium tetraphenylborate. When the influence of the applied potential and of the flow-injection variables on the determination of tetrabutylammonium was studied, a linear relationship was observed between current peak height and ion concentration over a range of 5 x 10^-6-6 x 10^-5 M tetrabutylammonium. Good repeatability and between-day reproducibility and high sample frequency were obtained. The effect of other ions was studied. Two different amperometric methods, indirect and direct, were also developed for the determination of dodecylsulfate in the concentration range 3 x 10^-5-9 x 10^-4 M.

"Use Of A Carbon Paste Electrode Modified With Spinel-Type Manganese Oxide As A Potentiometric Sensor For Lithium Ions In Flow Injection Analysis"
Electroanalysis 2004 Volume 16, Issue 8 Pages 633-639
Marcos F. S. Teixeira*, &Eacute;der T. G. Cavalheiro, M&aacute;rcio F. Bergamini, Fernando C. Moraes, Nerilso Bocchi

Abstract: A potentiometric sensor constructed from a mixture of 25% (m/m) spinel-type manganese oxide (lambda-MnO2), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li+ against other alkali and alkaline-earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6 x 10^-5-1.0 x 10^-2 mol L-1 with a slope 78.9±0.3 mV dec-1 over a wide pH range 7-10 (Tris buffer), without interference of other alkali and alkaline-earth metals. For a flow rate of 5.0 mL min-1 and a injection sample volume of 408.6 L, the relative standard deviation for repeated injections of a 5.0 x 10^-4 mol L-1 lithium ions was 0.3%.

"Electrocatalysis Of Nitrate Reduction At Copper-nickel Alloy Electrodes In Acidic Media"
Electroanalysis 2004 Volume 16, Issue 7 Pages 532-538
Brett K. Simpson*, Dennis C. Johnson

Abstract: The cathodic reduction of NO3- in 1.0 M HClO 4 is investigated by voltammetry at pure Ni and Cu electrodes, and three Cu-Ni alloy electrodes of varying composition, all configured as rotated disks. Voltammetric data obtained using these hydrodynamic electrodes demonstrate significantly improved activity for NO3- reduction at Cu-Ni alloy electrodes as compared to the pure Ni and Cu electrodes. This observation is explained on the basis of the synergistic benefit of different surface sites for adsorption of H-atoms, generated by cathodic discharge of H+ at Ni-sites, and adsorption of NO3- at Cu-sites on these binary alloy electrodes. Koutecky-Levich plots indicate that the cathodic response for NO3- at a Cu 75Ni25 electrode corresponds to an 8-electron reduction, which is consistent with production of NH3. In comparison, the cathodic response at Cu50Ni50 and Cu25Ni 75 electrodes corresponds to a 6-electron reduction, which is consistent with production of NH2OH. Flow injection data obtained using Cu50Ni50 and CU25Ni75 electrodes with 100-?L injections exhibit detection limits for NO 3- of ~0.95 ?M (ca. 95 pmol) and 0.60 ?M (ca. 60 pmol), respectively.

"Batch Injection Analysis: An Almost Unexplored Powerful Tool"
Electroanalysis 2004 Volume 16, Issue 7 Pages 513-523
Maria S. M. Quintino, L&uacute;cio Angnes*

Abstract: The main purpose of this review is to report the development and potentialities of batch injection analysis (BIA) and call the attention of researchers about the power of this (until now) almost unexplored tool. The text focuses on the concepts and potentialities of BIA combined with other techniques for analytical purposes. The association of BIA with amperometry, potentiometry, voltammetry, calorimetry, fluorescence and spectrophotometry is presented and important aspects related with each technique are discussed. Some aspects comparing the similarities and differences between BIA, FIA and wall-jet are presented along the text.

"Design Of An Interference-Free Cholesterol Amperometric Biosensor Based On The Electrosynthesis Of Polymeric Films Of Diaminonaphthalene Isomers"
Electroanalysis 2004 Volume 16, Issue 6 Pages 497-504
Esperanza Garc&iacute;a-Ruiz, Juan Carlos Vidal*, Mar&iacute;a Teresa Aramend&iacute;a, Juan Ram&oacute;n Castillo

Abstract: Different cholesterol amperometric biosensors were developed based on entrapment of cholesterol esterase and/or cholesterol oxidase in polymer films of diaminonaphthalene isomers, electrochemically synthesised from aqueous solutions of the monomers and enzymes in phosphate buffer at neutral pH. These conditions permit the growth of films with extraordinary selective properties which allow the preparation of interference-free biosensors for application in biological media without the response being affected by the presence of either endogenous species (ascorbic and uric acid) or exogenous species like 4-acetamidophenol. These selective properties were evaluated for the different monolayer and bilayer configurations proposed in function of the film permeation factor. All the steps involved in the preparation of the biosensors and determination of free or total cholesterol were carried out in a flow system. A comparative study was made of the analytical properties of each of the configurations developed and their application to the flow-injection determination of cholesterol in a synthetic serum.

"Critical Comparison Of Four Simple Adaptors For Flow Amperometric And Stripping Voltammetry With Mercury Drop Electrodes In Batch Cells"
Electroanalysis 2004 Volume 16, Issue 5 Pages 391-398
Andrea Cavicchioli, Daniela Daniel, Ivano Gebhardt Rolf Gutz*

Abstract: Electrochemical batch cells with mercury drop electrodes, MDEs, are readily available from a number of producers and widely used in electroanalysis for polarography, voltammetry and stripping voltammetry. To increase sample throughput and reduce reagent and sample consumption, the tendency is to couple the MDE with flow analysis systems (e.g., FIA, SIA or BIA). Many special flow cells for MDEs are described in the literature, but it is easier to convert existing commercial batch cells to flow operation. To assess the performance of such flow adaptors, four models were chosen because they are directly fitted to the glass capillary of any MDE, light enough not to impair the mechanical drop knocker and can be effortlessly built in the laboratory. They were all found adequate for flow amperometry and stripping voltammetry, with differences in sensitivity, flow rate dependence, response time, drop stability, tolerance to bubbles, uncompensated resistance and recontamination of disposed analyte from the electrolytic bath. Two of them, a simple L-shaped PTFE tube and an upstream nozzle holder made from a disposable pipette tip, gather a larger set of desirable features.

"Electrooxidation And Amperometric Detection Of Ascorbic Acid At GC Electrode Modified By Electropolymerization Of N,N-dimethylaniline"
Electroanalysis 2004 Volume 16, Issue 4 Pages 289-297
Protiva Rani Roy, Madhu Sudan Saha, Takeyoshi Okajima, Takeo Ohsaka *

Abstract: The polymer film of N,N-dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N-dimethylaniline (PDMA) film-coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (?): 0.3 ± 0.02 ?m) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag|AgCl|NaCl(sat)) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film-coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (Ds) were estimated by rotating disk electrode voltammetry: D = (5.5 ± 0.1) x 10 -6 cm2 CM2 s-1 and Ds = (6.3 ± 0.2) x 10^-8, (6.0 ± 0.2) x 10 -8 and (4.7 ± 0.2) x 10^-8 cm2 s-1 for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential-step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 ?M to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 ?M AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 ?A cm-2 ?M-1. So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film-coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice.

"Development Of An Amperometric Biosensor For -N-Oxalyl-L-,-Diaminopropionic Acid (-ODAP)"
Electroanalysis 2004 Volume 16, Issue 4 Pages 268-274
Negussie W. Beyene, Helmut Moderegger, Kurt Kalcher*

Abstract: An amperometric method for the determination of the neurotoxic amino acid -N-oxalyl-L-,-diaminopropionic acid (-ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulk-modified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion-film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/AgCl), flow rate 0.2 mL min-1, and carrier composition 0.1 mol L-1 phosphate buffer (pH 7.75). The same conditions were used for the determination of -ODAP. The signal was linear within the concentration range 53-855 mol L-1 glutamate and 195-1950 mol L-1 -ODAP. Detection limits (as 3 value) for both analytes were 9.12 and 111.0 mol L-1, respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on-line use.

"An Electrochemical Flow Analysis System For Putrescine Using Immobilized Putrescine Oxidase And Horseradish Peroxidase"
Electroanalysis 2004 Volume 16, Issue 4 Pages 260-267
Coralie Saby, Tien V. Nguyen, John H. T. Luong*

Abstract: An electrochemical flow analysis system was optimized together with immobilized putrescine oxidase and horseradish peroxidase for putrescine measurement. Four coupling agents, suberic acid bis(N-hydroxysuccinimide ester), -maleimidobutyric N-hydroxysuccinimide ester, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and glutaraldehyde, were used for immobilizing the two enzymes on porous aminopropyl glass beads to form a bienzymic detection column. Although the glutaraldehyde crosslinking procedure offered the highest response, the immobilized bienzyme system was responsive to putrescine, spermidine (123% of the putrescine response at 250 M) and cadaverine (98% of the putrescine response). In contrast, the enzymes immobilized on the glass beads using suberic acid bis(N-hydroxysuccinimide ester) offered significantly better selectivity towards putrescine at the same concentration. For comparison, cadaverine and spermidine only provoked a response of 4.7% and 27.5% of the putrescine signal. The response to cadaverine and spermidine was further suppressed by lowering the detection pH from 8 to 7. At 250 M, the response obtained for cadaverine and spermidine was only 1.5% and 3.9%, respectively, of the signal obtained for putrescine. A linear response to putrescine was obtained from 5 to 75 M (0.629 As M-1, R2=0.997) with a detection limit of 5 M (S/N=3). The amperometric response retained 75% of its initial value after 600 repeated injections. The immobilized PUO/HRP (putrescine oxidase/horseradish peroxidase) was successfully demonstrated for measuring putrescine in fish extracts as an indicator of fish spoilage.

"Flow Injection Amperometric Detection At Enzyme-Modified Gold Nanoelectrodes"
Electroanalysis 2004 Volume 16, Issue 3 Pages 190-198
Marc Delvaux, Sophie Demoustier-Champagne, Alain Walcarius

Abstract: Gold nanotubular electrode ensembles were prepared by using electroless deposition of the metal within the pores of polycarbonate particle track-etched membranes. Glucose oxidase (Gox), used as a model enzyme, has been immobilized onto preformed self-assembled monolayers (mercaptoethylamine or mercaptopropionic acid) on electroless gold via cross-linking with glutaraldehyde or covalent attachment by carbodiimide coupling. Flow-injection analysis systems in flow-through or wall-jet configurations using these Gox-modified nanoelectrodes are described. The influence of different experimental parameters (i.e., applied potential, flow rate, interferents) on the analytical response of the sensor to glucose has been evaluated. Under optimized conditions, very reproducible results (standard deviations <4%, n=38) were obtained, linear calibration was achieved in the 2 x 10^-4 M to 3 x 10^-2 M concentration range and the detection limit was 2 x 10^-4 M. Moreover, no significant interferences from species like ascorbic and uric acids were observed at a potential of +0.9 V.

"Nanoparticle-Structured Ligand Framework As Electrode Interfaces"
Electroanalysis 2004 Volume 16, Issue 1-2 Pages 120-126
Nancy N. Kariuki, Jin Luo, Li Han, Mathew M. Maye, Laura Moussa, Melissa Patterson, Yuehe Lin, Mark H. Engelhard, Chuan-Jian Zhong

Abstract: Nanostructured thin film assemblies derived from metal or oxide nanocrystal cores and functionalized molecular shells provide large surface-to-volume ratio and three-dimensional ligand frameworks. In this article, we report results of an investigation of the nanostructured materials for electroanalysis. Monolayer-capped gold nanoparticles of 2-nm core diameter and carboxylic acid-functionalized alkyl thiols were assembled on electrode surfaces via an exchange-crosslinking-precipitation reaction route, and were studied as a model system. The network assemblies exhibit open frameworks in which the void space forms channels with the nanometer sized cores defining its size and the shell structures defining its chemical specificity. Such nanostructures were exploited to demonstrate the viability of responsive materials for interfacial incorporation and fluxes of ionic species. The nanomaterials were characterized by an array of techniques, including cyclic voltammetry, electrochemical quartz-crystal nanobalance, flow injection analysis, and surface infrared reflection spectroscopy. The current responses and mass loading as a result of the incorporation of ionic species into the nanostructure have been analyzed. The potential application of the nanostructured thin films for electrochemical detection in microfluidic systems is also discussed.

"Development Of A Dual-Band Amperometric Detector For Determination Of Ascorbic Acid And Glucose"
Electroanalysis 2003 Volume 15, Issue 23-24 Pages 1884-1889
Thiago R. L. C. Paix&atilde;o, Renato Camargo Matos, Mauro Bertotti*

Abstract: A flow-through system cell that allows the direct and simultaneous amperometric determination of ascorbic acid and glucose to be performed is described. The electrolytic cell in a thin layer configuration is composed of a gold and a copper-modified electrode, polarized at -0.10 and 0.50 V, respectively. By using a 1 mol L-1 NaOH solution as carrier electrolyte, amperometric data acquisition was performed simultaneously with a bipotentiostat and the results were analyzed by a multivariate calibration method. Measurements for two commercial pharmaceutical products were carried out without any pretreatment and showed a good correlation with data obtained by using recommended methods. The use of the device to the on-line quantitative removal of interfering species at the copper electrode is also discussed.

"Application Of Prussian Blue Based Composite Film With Functionalized Organic Polymer To Construction Of Enzymatic Glucose Biosensor"
Electroanalysis 2003 Volume 15, Issue 23-24 Pages 1843-1849
Katarzyna Derwinska, Krzysztof Miecznikowski, Robert Koncki, Pawel J. Kulesza*, Stanislaw Glab, Marcin A. Malik

Abstract: We describe and characterize an amperometric biosensor utilizing the electrocatalytic reduction of hydrogen peroxide at a glassy carbon electrode modified with a novel composite film of Prussian Blue and polypyrrole derivative, polymerized 4(pyrrole-1-yl) benzoic acid, overcoated with the covalently bound glucose oxidase enzyme. The addition of a functionalized organic component to Prussian Blue permits permanent attachment of an enzyme, exhibits an overall stabilizing effect, and it seems to support fast propagation of charge within the Prussian Blue based composite film. Preliminary diagnostic experiments have been done using cyclic voltammetry, chronocoulometry and rotating disk volatmmetry. The rate of hydrogen peroxide reduction at the composite film in the potassium containing phosphate buffer (pH 6) is expected to be very fast because the overall process is controlled by diffusion of hydrogen peroxide in solution. The fact that the reduction of enzymatically produced hydrogen peroxide proceeds at a fairly negative potential, 0 V (vs. SCE) (pH 6), makes the system largely free of common interferences (e.g., ascorbic acid or uric acid). The proposed biosensor permitted reproducible and reliable determinations of glucose in real (i.e., in pharmaceutical and food) samples also under the flow-injection analysis conditions. The detection limit and sensitivity have been found to be on the level of 1 x 10^-5 mol L-1 and 0.7 A/1 mmol L-1 (2.5 A/cm2/1 mmol L-1), respectively.

"Nonmonotonic Transient Potential Signals With An 18-Crown-6 Based Ion-Selective Electrode In A Flow-Injection System"
Electroanalysis 2003 Volume 15, Issue 19 Pages 1536-1540
Joaqu&iacute;n A. Ortu&ntilde;o, Concepci&oacute;n S&aacute;nchez-Pedre&ntilde;o*, Domingo Martinez

Abstract: The dynamic potential response of an 18-crown-6 based ion-selective electrode towards Li+, Na+, K+ and Ca2+, in a flow-injection system is studied. Different double nonmonotonic transient signals are obtained for the different ions. The influence of the flow-injection variables and of ion concentration on the signals is studied. Two signal parameters, the relative return rates, are found to be characteristic for each ion and are constant for a concentration range of 1-3 decades. The nonmomotonic transient signals obtained are explained by reference to the theoretical models reported.

"Flow Injection Analysis Of Ascorbic Acid In Real Samples Using A Highly Stable Chemically Modified Screen-printed Electrode"
Electroanalysis 2003 Volume 15, Issue 14 Pages 1171-1176
Jyh-Myng Zen, Dong-Mung Tsai, Annamalai Senthil Kumar

Abstract: A silica sol-gel glass-coated ferricyanide-doped Tosflex-modified screen-printed electrode (designated as SG/FeCN-Ts/SPE) was used for the mediated oxidation of ascorbic acid in neutral pH. The sol-gel overlayer was found to stabilize the Fe(CN)63--Tosflex system without any foul-off and deterioration behavior through chemical interaction between the hydrophilic sites of Tosflex and oxy- and/or -hydroxy surface functional groups of silicate. The electrochemical mediation of ascorbic acid was found to follow the Michaelis-Menten kinetic pathway. The SG/FeCN-Ts/SPE was very stable for repetitive measurements by flow injection analysis at 0.3 V (vs. Ag/AgCl). A linear calibration plot was obtained for ascorbic acid determination up to 300 ?M with sensitivity and detection limit (S/N = 3) of 2.85 nA/?M and 46 nM, respectively. The system also showed tolerable interference to uric acid, urea and carbohydrates and was used for the determination of ascorbic acid in human urine, clinical tablet and apple juice.

"New Strategy For Dehydrogenase Amperometric Biosensors Using Surfactant To Enhance The Sensitivity Of Diaphorase/Ferrocene Modified Carbon Paste Electrodes For Electrocatalytic Oxidation Of NADH"
Electroanalysis 2003 Volume 15, Issue 13 Pages 1095-1100
C&eacute;sar Ram&iacute;rez-Molina, Mohammed Boujtita, Nabil El Murr

Abstract: A carbon paste electrode (CPE) modified with diaphorase (DAP) and ferrocene (FcH) has been developed for determination of NADH at low working potential. The sensitivity and operational stability, towards the detection of the reduced form of the nicotinamide adenine dinucleotide (NADH) in flow injection analysis (FIA), were greatly improved (5 times) upon adding Tween 20 into the electrode matrix. The magnitude of the amperometric signal was dependent on DAP, FcH and surfactant loading, into the modified carbon paste electrode. A rapid and repeatable response was observed to the variation of NADH concentration in the vicinity of the electrode surface. Such advantages of the DAP/FcH/Tween 20 modified carbon paste were successfully used in the construction of L-lactate dehydrogenase modified electrodes. The use of this new approach can be generalized to other dehydrogenases and represents a decisive step for a versatile preparation method of amperometric biosensors.

"Disposable Glucose Sensors For Flow Injection Analysis Using Substituted 1,4-Benzoquinone Mediators"
Electroanalysis 2003 Volume 15, Issue 11 Pages 975-981
King-Tong Lau, Stephane A. L. de Fortescu, Lindy J. Murphy*, Jonathan M. Slater*

Abstract: The redox chemistry of several substituted benzoquinones was investigated by cyclic voltammetry at a glassy carbon electrode and candidates for inclusion in a mediated biosensor for use in flow analysis were selected on the basis of oxidation potential, electrochemical reversibility and solubility. Glucose sensors constructed by sequential deposition onto a carbon pellet of 2,6-dimethyl-1,4-benzoquinone, 2,3,5,6-tetramethyl-1,4-benzoquinone or phenyl-1,4-benzoquinone mediator solution, followed by glucose oxidase in polyvinylalcohol-Nafion solution, were tested for response to glucose using flow injection analysis. Sensors prepared from 2,6-dimethyl-1,4-benzoquinone gave highest sensitivity, with a linear range of response to glucose of 2.5-40 mM. The use of an enzyme-free comparative electrode to eliminate the response from interferents was investigated.

"Renewable Drops Electrochemical Sensor For Sulfide Ions Detection"
Electroanalysis 2003 Volume 15, Issue 9 Pages 827-830
M. R. Milani, N. R. Stradiotto, A. A. Cardoso

Abstract: The design and characteristics of a novel electrochemical system, which uses a drop as a renewable electroanalytical sensor, are described. This article describes the performance of the electrochemical system, the coupling of the experimental arrangement with flow injection technique and a demonstration of its applicability for the measurement of sulfide. The method is based on renewable drops of ferricyanide ions, buffered by borate. The ferrocyanide ions, product of the reaction between ferricyanide and sulfide ions, are oxidized on a platinum microelectrode and the current measured is related to sulfide concentration. The measurements can be done in continuous or static flow mode. In continuous mode, the detection limit is 5.0 x 10^-5 mol L^-1.

"Voltametric And Flow Injection Determination Of Oxytetracycline Residues In Food Samples Using Carbon Fiber Microelectrodes"
Electroanalysis 2003 Volume 15, Issue 7 Pages 601-607
L. Ag&uuml;&iacute;, A. Guzman, M. Pedrero, P. Y&aacute;&ntilde;ez-Sede&ntilde;o, J. M. Pingarr&oacute;n*

Abstract: A voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1 mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square-wave conditions, a linear calibration plot for OTC was obtained in the 1.0 x 10^-6-1.0 x 10^-4 mol L-1 range, with a detection limit of 2.9 x 10^-7 mol L-1 (150 ng mL-1) OTC. The determination of OTC by a flow-injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100 ng mL-1 and 200 ng g-1 levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile -5.0 x 10^-4 mol L-1 tetrabutylammonium perchlorate medium. Recoveries of 96±8 and 91±8% were obtained for milk and eggs, respectively, by applying the standard additions method.

"A Voltammetric Assay Of Antioxidants And Inhibitors Of Soybean Lipoxygenase"
Electroanalysis 2003 Volume 15, Issue 5-6 Pages 573-578
Pascal P&eacute;russe, D&oacute;nal Leech*

Abstract: Antioxidant activity and/or the inhibition of lipoxygenases may contribute to the cell and tissue protective properties of flavonoids. Soybean lipoxygenase-1 (LOX-1), is a useful paradigm for lipoxygenases isolated from different sources, and can be used to devise assays of oxygenase inhibitors and antioxidants. Here we describe the voltammetric detection of methylene blue (MB) to assay for antioxidant and lipoxygenase inhibition activity. MB is formed by the catalytic action of hydroperoxide, produced by soybean lipoxygenase reaction on linoleic acid, on benzoyl-leuco methylene blue (BLMB). Every compound which blocks either the enzymatic reaction, lipoxygenase inhibitors, or the oxidation of BLMB, antioxidants, can thus be detected using this method. The assay involves reaction for a period of one hour of linoleic acid, lipoxygenase, BLMB and inhibitor, followed by injection into a flow-injection system and detection by square-wave voltammetry of the methylene blue produced. The problem of irreproducibility induced by adsorption at the solid platinum working electrode is alleviated using the method of alternate injections of control and assay solutions. Assays of several known lipoxygenase inhibitors were undertaken. All of these inhibitors were also, however, shown to be antioxidants. Extension of the assay to the rapid evaluation of novel therapeutic antioxidants and lipoxygenase inhibitors is proposed.
Antioxidants Enzyme, lipoxygenase Voltammetry

"Permselective Properties Of Electropolymerized Guaiacol Derivatives"
Electroanalysis 2003 Volume 15, Issue 5-6 Pages 529-532
Grzegorz Milczarek*, Aleksander Ciszewski

Abstract: Guaiacol (2-methoxyphenol) and its 5 derivatives such as 4-allyl-2-methoxyphenol,2-methoxy-4-propenylphenol, 2-methoxy-4-propylphenol, 4-hydroxy-3-methoxybenzylamine and 4-chloro-2-methoxyphenol were oxidatively polymerized on platinum electrodes in 0.1 M NaOH solution. The polymer modified electrodes were then checked for their responses towards biologically important analytes such as hydrogen peroxide, ascorbic and uric acids, dopamine and acetaminophen under flow injection conditions. The effect of a monomer chosen on the permselective properties of the deposited film is thoroughly discussed. Feasibility of the application of these polymer modified electrodes in selective flow injection detection of hydrogen peroxide and dopamine is demonstrated.

"Determination Of Mobile Thallium In Soil By Flow Injection Differential Pulse Anodic Stripping Voltammetry"
Electroanalysis 2003 Volume 15, Issue 5-6 Pages 480-483
Zenon Lukaszewski*, Bozena Karbowska, Wlodzimierz Zembrzuski

Abstract: A procedure for the determination of mobile thallium in soil has been developed. Free thallium(I) was extracted with deionized water, while the sorbed and exchangeable metal was extracted with 1 M ammonium nitrate. Thallium in extracts was determined by differential-pulse anodic stripping voltammetry in a flow-injection system with medium circulation. 0.05 M EDTA was the base electrolyte. The procedure was applied for the determination of mobile thallium in a sample of ground from a waste dump which was a potential source of thallium pollution. The total concentration of thallium in the sample was 17.9 µg g-1. 3.97±0.25% of total thallium was found to be water soluble and 12.4±1.1% was sorbed and exchangeable. An attempt to determine the thallium bound to the carbonate fraction failed because of the high accumulation of interfering lead in this fraction. A single extraction cycle recommended by the literature was not sufficient to extract the whole thallium content of the fraction. Minor rivers of the area of the waste dump have a thallium concentration higher by two orders of magnitude than in reference rivers.

"Flow-Injection Analysis Of Residual Glucose In Wines Using A Semiautomatic Analyzer Equipped With A Prussian Blue-Based Biosensor"
Electroanalysis 2003 Volume 15, Issue 5-6 Pages 447-451
E. A. Ulasova, L. Micheli, L. Vasii, D. Moscone, G. Palleschi, S. V. Vdovichev, A. V. Zorin, S. A. Krutovertsev, E. E. Karyakina, A. A. Karyakin*

Abstract: The Prussian Blue modified glassy-carbon (GC) electrode assembled with glucose oxidase (GOD) immobilized in Nafion on the top of the electrode surface area has been inserted in a wall-jet cell connected to a semiautomatic analyzer, which controls all the operations for carrier buffer, flow and sample injection. The Prussian Blue based glucose biosensor inserted in the FIA analyzer has shown linear response to glucose at an applied potential of 0.0 V (Ag/AgCl) in the range of 10^-6-10-3 M. Residual glucose has been detected in red and white wines. A dilution of 1 : 1000 has been used for all the wines tested. Neither matrix effect, nor electrochemical interferences were observed. A comparison with a spectrophotometric glucose kit gave excellent correlation for levels of glucose detected. FIA analyzer compared with the standard analytical kit resulted in simplified procedures and a reduced time for the analysis.

"Electroanalytical Flow Measurements-Recent Advances"
Electroanalysis 2003 Volume 15, Issue 5-6 Pages 347-365
Marek Trojanowicz, Malgorzata Szewczynska, Marzena Wcislo

Abstract: As general trends in current development of chemical analysis, including electroanalysis, one can indicate a search for methods fast and multianalyte, for miniaturized measuring devices, mechanization and automation of analytical processes. In all these trends a significant role is played by measurements in flow conditions. The major advantage of flow electroanalysis is a possibility of utilizing a kinetic discrimination in potentiometric measurements and enhancement of mass transport in voltammetric techniques. Flow injection techniques provide shortening of time of a single analytical determination due to reproducible use of transient signal from the detector without need of obtaining a steady-state equilibrium signal. Electrochemical detection in HPLC gives often improved selectivity and detection limit for electroactive solutes, whereas in capillary electrophoresis it allows a convenient design of portable, integrated chips for field application. This review presents state-of-the -art of flow electroanalysis based on 226 cited literature references.

"A Study On The Electrochemical And Electrochemiluminescent Behavior Of Homogentisic Acid At Carbon Electrodes"
Electroanalysis 2003 Volume 15, Issue 3 Pages 208-218
Yuwu Chi, Jianping Duan, Zheng Feng Zhao, Hongqinq Chen, Guonan Chen

Abstract: The electrochemical oxidation and electrochemiluminescent behavior of homogentisic acid (HGA) has been studied in aqueous solutions over a wide pH range by linear sweep voltammetry, cyclic voltammetry, chronocoulometry at a glassy carbon electrode, by controlled potential electrolysis at a large area spectroscopic graphite electrode, and by spectroelectrochemistry at an optically transparent drilled holes graphite (DHG) electrode in a thin-layer cell. The studies reveal that the electrochemical oxidation of HGA at carbon electrodes is a reversible process involving two-electron, two-proton transfer. In addition to the electrochemical oxidation, the chemical oxidation of HGA by dissolved oxygen was investigated by spectroscopic method combined with voltammetry. It was revealed that HGA is fairly stable in strongly acidic media but readily oxidized by dissolved oxygen in alkaline media giving rise to 1,4-benzoquinone-2-acetic acid, the same product as that of electrooxidation of HGA. This oxidation product is stable in acidic, neutral and weakly alkaline media, but can further degrade in strongly alkaline media yielding oxalate as the final product. The electrochemiluminescent mechanism of HGA in the presence of Ru(bpy)32+ at a glassy carbon electrode was also investigated in detail, based on which a sensitive ECL method for determination of HGA was developed, and the detection limit was 3.0 x 10^-8 mol L-1.
Homogentisic acid Chemiluminescence Electrode Optimization

"Investigation Of The Effect Of Different Glassy Carbon Materials On The Performance Of Prussian Blue Based Sensors For Hydrogen Peroxide"
Electroanalysis 2003 Volume 15, Issue 3 Pages 175-182
Francesco Ricci, Giuseppe Palleschi, Yirgalem Yigzaw, Lo Gorton*, Tautgirdas Ruzgas, Arkady Karyakin

Abstract: Three different kinds of glassy carbon (GC-R, GC-K, GC-G) were equally pretreated, further modified with electrochemically deposited Prussian Blue and used as sensors for hydrogen peroxide at an applied potential of -50 mV (vs. Ag|AgCl). Their performance was evaluated with respect to the following parameters: the coverage and electrochemistry of the electrodeposited Prussian Blue, the sensitivity and the lower limit of detection for hydrogen peroxide, and the operational stability of the sensors. GC-R showed the best behavior concerning the surface coverage and the operational stability of the electrodeposited Prussian Blue. For this electrode the sensitivity for hydrogen peroxide (10 M) was 0.25 A/M cm2 and the detection limit was 0.1 M. Scanning electron microscopy was used to study the surfaces of the three electrodes before and after the electrodeposition of Prussian Blue and to search for the reason for the three different behaviors between the different glassy carbon materials. The Prussian Blue modified GC-R was also used for the construction of a glucose biosensor based on immobilizing glucose oxidase in Nafion membranes on top of electrodeposited Prussian Blue layer. The operational stability of the glucose biosensors was studied in the flow injection mode at an applied potential of -50 mV (vs. Ag|AgCl) and alternatively injecting standard solutions of hydrogen peroxide (10 M) and glucose (1 mM) for 3 h. For the GC-R based biosensor a 2.8% decrease of the initial glucose response was observed.

"Electroimmobilization Of MAO Into A Polypyrrole Film And Its Utilization For Amperometric Flow Detection Of Antidepressant Drugs"
Electroanalysis 2003 Volume 15, Issue 2 Pages 133-138
M. H. Vela, Djane S. de Jesus, Cristina M. C. M. Couto, Alberto N. Ara&uacute;jo, M. C. B. S. M. Montenegro

Abstract: The preparation of a biosensor based on the enzymatic immobilization in polypyrrole polymer for the detection of antidepressant drugs is described. The enzyme monoamine oxidase (MAO) was immobilized by electropolymerization of pyrrole around a platinum electrode, at a constant potential of +0.75 V (vs. Ag/AgCl) in such a way to obtain a membrane thickness, which was constant and equal to 100 mC/cm2. The biosensor was obtained from a 0.1 M KCl saline solution containing pyrrole at a concentration equal to 0.4 M and 2.5 mU/mL of MAO. The biosensor was adapted to a continuous flow injection analysis system (FIA) with the amperometric detection of hydrogen peroxide produced by enzymatic reaction carried out at a potential of +0.7 V (vs. Ag/AgCl), pH 7.4 and temperature of 37°C. In optimized flow conditions, the biosensor presented an analytical response for fluoxetine in the interval between 0.67 and 4.33 mM, with a detection limit of 0.10 mM. The analytical use of the biosensor developed was evaluated through analysis of commercial pharmaceutical products containing fluoxetine, available on the Portuguese market. The amperometric flow results obtained do not differ significantly from the values resulting from analysis of the same products by the method proposed by the US Pharmacopeia, with sampling rates of 20-25 samples/hour.

"Enhancement Of Anodic Response For DMSO At Ruthenium Oxide Film Electrodes As A Result Of Doping With Iron(III)"
Electroanalysis 2003 Volume 15, Issue 2 Pages 97-102
Brett K. Simpson, Dennis C. Johnson*

Abstract: The oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone (DMSO2) is representative of numerous anodic oxygen-transfer reactions of organosulfur compounds that suffer from slow kinetics at noble metal electrodes. Anodic voltammetric data for DMSO are examined at various RuO2-film electrodes prepared by thermal deposition on titanium substrates. The response for DMSO is slightly larger at RuO2 films prepared in a flame as compared with films prepared in a furnace; however, temperature is more easily controlled in the furnace. Doping of the RuO2 films with Fe(III) further improves the sensitivity of anodic response for DMSO. Optimal response is obtained at an Fe(III)-doped RuO2-film electrode prepared using a deposition solution of 50 mM RuCl3 and 10 mM FeCl3 in a 1 : 1 mixture of isopropanol and 12 M HCl at an annealing temperature of 450°C. The Levich plot (i vs. 1/2) and Koutecky-Levich plot (1/i vs. 1/1/2) of amperometric data for the oxidation of DMSO at an Fe(III)-doped RuO2-film electrode configured as a rotated disk are consistent with an anodic response controlled by mass-transport processes at low rotational velocities. Flow injection data demonstrate that Fe(III)-doped RuO2-film electrodes exhibit detection capability for methionine and cysteine in addition to DMSO. Detection limits for 100-L injections of the three compounds are ~3.2 x 10^-4 mM, i.e., ~32 pmol.

"Batch Injection Analysis Utilizing Modified Electrodes With Tetraruthenated Porphyrin Films For Acetaminophen Quantification"
Electroanalysis 2002 Volume 14, Issue 23 Pages 1629-1634
Maria S. M. Quintino, Koiti Araki, Henrique E. Toma, L&uacute;cio Angnes*

Abstract: Batch injection analysis (BIA) utilizing amperometric detection with glassy carbon electrodes modified with [Co(TPyP){Ru(bipy)2Cl}4](TFMS)5H2O porphyrin films were explored for acetaminophen analysis in pharmaceutical formulations. BIA is an interesting alternative for application of electrodes modified with tetraruthenated porphyrins. This sensor exhibited sharp current response peaks, rapid washout and excellent reproducibility for BIA-amperometric quantification of acetaminophen. Also, a wide linear working range (10-4 to 10^-6 mol L-1) as well as high sensitivity and sampling frequency rate (detection limit=1.1 x 10^-7 mol L-1, sampling frequency=120 injections/h) and a small volume of analysis (100 L/injection) was achieved. Furthermore, the proposed method permits the direct quantification of acetaminophen in many pharmaceutical products, avoiding cumbersome processes as previous separations, solvent extraction or sample filtration. The new procedure was applied to the analysis of commercial pharmaceutical products and the results were in excellent agreement with the ones obtained by spectrophotometric method. Accordingly, this amperometric method showed to be very well suited for quality control analysis and other applications with similar requirements.

"Feedback Based Continuous Flow Titrations With Electrogenerated Titrants"
Electroanalysis 2002 Volume 14, Issue 19-20 Pages 1383-1390
Purnendu K. Dasgupta, Kyoo Dong Jo

Abstract: We describe the use of electrogenerated titrants in continuous feedback-based flow titrations. In previous studies from this laboratory (Anal. Chem. 2000, 72, 4713; Anal. Chim. Acta. 2001, 435, 289) the flow rate of a titrant was varied linearly in response to a controller output voltage (Vc). In the present article, the status of the controller output (positive or negative ramping) is governed in a binary fashion by a sensor output and the controller output voltage linearly controls the electrical current applied to an electrochemical titrant generator. The volumetric flow rate of the generated titrant remains constant, but its concentration varies linearly with Vc. The ultimate titration accuracy and precision in previous studies where flow was varied depended on flow accuracy and reproducibility, here they depend on more easily controlled/accurately known parameters, electrical current and coulometric reagent generation efficiency at a constant flow rate. The system has been tested by applying it to titrations of As(III), thiosulfate, sulfite, metabibisulfite and sulfide using electrogonerated iodine. The titration mixture is monitored optically (as well as potentiometrically, for sulfide). This principle permitted continuous true titrations with good precision and speed (typ. <1.5% relative standard deviation (RSD) with less than 30 s/titration with photometric detection, typ. 1.25% RSD with under 60 s/titration with potentiometric detection for sulfide).

"Evaluation Of Electrochemical Release Of Self-assembled Reagents As A Component Of A Preconcentrator For Flow Injection Analysis"
Electroanalysis 2002 Volume 14, Issue 19-20 Pages 1339-1343
Long Cheng, Janaki Seneviratne, Gilbert E. Pacey, James R. Gord, Michael S. Brown, Terrence S. Meyer, James A. Cox

Abstract: Demonstrated is that self-assembled monolayers anchored to gold by a thiolate can trap an analyte and electrochemical release of the assembly into a carrier allows determination at a downstream detector. Quantitative potentiostatic release of a coumarin derivative is demonstrated by fluorometry. The capture Of PMo12O403- on a monolayer of 4-aminothiophenol followed by oxidative release results in a 4.8 nA peak (1.6-s width at 1 mL min-1) for the four-electron reduction Of PMo12O403-. The sensitivity is increased by forming multilayers on the pre-concentrator. Release of 10 layers of P2W18O626- yields a 12.4 nA peak even though only a one-electron reduction occurs at the potential employed.
Preconcentration Desorption

"Determination Of Pesticides Using Electrochemical Enzymatic Biosensors"
Electroanalysis 2002 Volume 14, Issue 19-20 Pages 1311-1328
Marek Trojanowicz

Abstract: In the recent decade numerous biosensing methods for detection of pesticides have been developed using integrated enzymatic biosensors and immunosensors. Enzymatic determination of pesticides is most often based on inhibition of the activity of selected enzymes such as cholinesterases, organophosphate hydrolase, alkaline and acid phosphatase, ascorbate oxidase, acetolactate synthase and aldehyde dehydrogenase. Enzymatic biosensors were developed using various electrochemical signal transducers, different methods of enzyme immobilization and various measuring methodologies. Application of single-use screen-printed biosensors in batch measurements and flow injection analysis with enzyme biosensors are most intensively developed procedures. An improvement of detectability level can be achieved by the use of recombinant enzyme mutants, while multi-component determinations by the use of biosensor matrices and data processing with artificial neural networks. In some cases the determined pesticide can be also a substrate of enzymatic reaction. Another area of development of biosensors for determination of pesticides is in the design of microbial biosensors and photosystem-based biosensors with electrochemical biosensors.

"Anodic Stripping Voltammetric Determination Of Mercury In Water By Using A New Electrochemical Flow Through Cell"
Electroanalysis 2002 Volume 14, Issue 18 Pages 1288-1293
Pablo Richter, M. In&eacute;s Toral, Bernardo Abbott

Abstract: A flow through electrochemical cell was designed for the implementation of a simple, efficient, rapid and sensitive method for determination of mercury in water samples by anodic stripping voltammetry. A solid gold or a gold film electrode can be used as working electrode in a wall-jet configuration of the cell. The analyte is electrolyzed on the electrode surface by pumping the liquid sample through a continuous flow manifold at a flow rate of 8 mL/min. Deposition efficiency increased by increasing the velocity at which the sample arrives to the cell. After deposition of the analyte, it was stripped from the electrode by using a linear anodic potential scan at 35 mV/s. Geometric and hydrodynamic variables of the system were studied in order to optimize the analytical response. A detection limit of 0.05 ng/mL was reached by using a pre-concentration time of 540 s. The repeatability expressed as relative standard deviation was always less than 3%. The method shows a good selectively and was successfully applied to the determination of mercury in different water samples.
Preconcentration

"Amperometric Detection Of Peroxides Using Peroxidase And Porphyrin Biomimetic Modified Electrodes"
Electroanalysis 2002 Volume 14, Issue 17 Pages 1157-1164
E. Baldini, V. C. Dall'Orto, C. Danilowicz, I. Rezzano, E. J. Calvo

Abstract: Biosensors designed with crosslinked redox hydrogel and horseradish peroxidase have been evaluated in aqueous and nonaqueous media. Electrodes made of a single layer of active material were prepared with Os(bYP)(2)ClPyCH2 NHPoly(allylamine) polymer, (PAA-Os), attached to the enzyme by PEG-400 bifunctional reagent with the Os sites acting as electron wires. The electrodes proved to be stable in the presence of organic solvent considering the time evolution of the redox charge and the catalytic current. However, a reasonable decrease in the enzyme response is apparent while increasing solvent content in solution for detection of hydrogen and lauroyl peroxide. As an alternative biomimetic strategy, electrodes were modified with consecutive layers of PAA-Os and electropolymerized Fe-protoporphyrin IX. The electrochemical detection of peroxides was also possible with this system, proving that the poly[Fe-protoporphyrin IX]/Osmium complex system can mimic the peroxidase activity towards hydrogen and organic peroxides. The replacement of Fe-protoporphyrin by Ni-protoporphyrin IX and PAA-Os by PAA in different experiments demonstrates that the mechanism for peroxide reduction involves both Os and Fe-protoporphyrin IX sites. The enzymatic electrodes were applied to benzoyl peroxide quantitation in a pharmaceutical product. The method validation demonstrates that a simple and rapid FIA detection can be applied.
Enzyme Catalysis

"Characterization Of A Glutamate Biosensor Based On A Novel Glutamate Oxidase Integrated Into A Redox Hydrogel"
Electroanalysis 2002 Volume 14, Issue 15-16 Pages 1052-1059
Ekaterina Mikeladze, Alexandra Collins, Marina Sukhacheva, Alexander Netrusov, Elisabeth Cs&ouml;regi

Abstract: A newly isolated and purified glutamate oxidase was used to construct amperometric biosensors for glutamate monitoring. The enzyme-producing microorganism belongs to the genus of Streptomyces - Streptomyces sp. Z-11-6 - and is capable of producing extracellular L-glutamate oxidase. The microorganism was obtained by mutagenesis with HNo2 from a parent strain isolated from soil of Lypetskaya region, Russia, followed by conventional screening methods. The developed biosensor is based on a coupled enzyme system (glutamate oxidase and horseradish peroxidase), the enzymes being crosslinked to a redox polymer (PVI19-dmeOs) using poly(ethylene glycol) diglycidyl ether as crosslinker. ne characteristics of the obtained biosensors were compared with those obtained for similarly constructed electrodes based on a commercially available glutamate oxidase from Yamasa Corp., Japan. The biosensors were operated at - 50 mV (vs. Ag/AgCl 0.1 M KCl) in a flow injection system. Special attention has been focused on the selectivity of the biosensors, evaluating their responses in the presence of several potentially interfering substances, possibly present in brain microdialysates (ascorbic acid, aspartate, cysteine, dopamine, DOPAC, GABA, glutamine, glycine, 5-HIAA, HMPG, HVA, serotonin, tryptophan, tyrosine and uric acid). The biosensors based on the two enzymes displayed similar bioanalytical characteristics but different selectivity patterns.

"Flow Injection Analysis Of Aziprotryne Using An Electrochemical Sensor Based On Cobalt Phthalocyanine Modified Carbon Paste Electrode"
Electroanalysis 2002 Volume 14, Issue 13 Pages 892-898
Manuel Chicharro, Antonio Zapardiel, Esperanza Bermejo, Elena Madrid, Cristina Rodr&iacute;guez

Abstract: The detection and determination of aziprotryne in flow injection analysis with an amperometric method based on a carbon paste electrode modified with phthalocyanine is described. The concentrations of herbicide in acidic solutions were determined using the electrocatalytic reduction signal corresponding to herbicide reduction at this kind of electrode. A detection limit of 9 ng/mL (0.9 ng aziprotryne) was obtained for a sample loop of 100 µL at a fixed potential of - 130 mV (vs. Ag/AgCl) in 0.1 M perchloric acid and a flow rate of 4.0 mL/min. The developed method was applied to determine aziprotryne in environmental and tap water samples; using a prior solid-phase extraction step, aziprotryne concentrations lower than 0.2 ng/mL could be measured. Furthermore the modified carbon paste electrodes offered reproducible responses in such system, and the relative standard deviation was 3.1% using the same surface and 4.6% for different surface. The response of the electrodes was stable, with more than 98% of the initial retained activity in the first 35 minutes of continuous use.
Graphite

"Relocation Of A Tubular Voltammetric Detector For Standard Addition In FIA"
Electroanalysis 2002 Volume 14, Issue 11 Pages 741-746
Rita I. L. Catarino, M. Beatriz Q. Garcia, Jos&eacute; L. F. C. Lima, E. Barrado, M. Vega

Abstract: In this work a new strategy for the automation of the standard addition method by FIA with voltammetric detection is described, based on the concept of multi-site detection. In the system developed, a single voltammetric detector with mobility in the FIA manifold, carried out sequential measurement of the sample plug before and after addition of the standard solution. The construction and evaluation of the voltammetric detector of tubular configuration and internal diameter similar to the tubing of the FIA manifold, whose incorporation in the system allowed the measurement process to be carried out without change of the hydrodynamic characteristics of the sample plug, is also mentioned. To evaluate the, usefulness of the proposed multi-site voltammetric detection system, this was used in the amperometric determination of ascorbic acid in fruit juices where the standard addition method is frequently required to overcome the matrix effect. The results obtained with the FIA system were compared with those from the reference procedure proposed by AOAC. No statistical difference between methods was found at the 95% confidence level. The relative deviations between both methods were always less than or equal to 3.8%. The sampling rate was about 55 samples per hour (110 measurements).
Ascorbic acid

"Electrochemical Investigation Of Glucose Sensor Fabricated At Copper-plated Screen-printed Carbon Electrodes"
Electroanalysis 2002 Volume 14, Issue 10 Pages 671-678
Annamalai Senthil Kumar, Jyh-Myng Zen

Abstract: Copper-plated screen-printed carbon electrode (CuSPE) provides a suitable catalytic surface for the amperometric detection of hydrogen peroxide, Glucose oxidase (GOD) is immobilized on the top of the CuSPF to form a glucose sensor. The interaction of copper oxide with GOD was found to be an important factor in the glucose detection. Preliminary investigation under hydrodynamic conditions showed a linear calibration plot up to 26.7 mM glucose with a slope and regression coefficient of 4.5 muA/mM and 0.9902. respectively. The Michaelis-Menten kinetics by nonlinear curve fitting yielded a K-m value close to that in solution indicating the ideality and suitability of the present system. Classical mixed potential mechanism is for the first time applied to the enzyme-coated CuSPE to further understand the system.
Glucose

"Flow Injection Analysis Of Allopurinol By Enzymeless Approach At Glassy Carbon Electrodes"
Electroanalysis 2002 Volume 14, Issue 10 Pages 645-649
Jyh-Myng Zen, Pei-Yan Chen, Annamalai Senthil Kumar

Abstract: Allopurinol is a pharmaceutical drug mainly used for the treatment of chronic gout. It is an antioxidant as well as a powerful inhibitor of xanthine oxidase. Very few electroanalytical assays were reported for allopurinol detection so far. No faradic process of allopurinol was observed by cyclic voltammetry at a glassy carbon electrode. A systematic decrease in current signal of ascorbic acid was observed upon the addition of allopurinol due to the inhibitory action. By taking ascorbic acid as the mobile phase, the above property was utilized to develop a sensitive detection scheme for allopurinol by flow injection analysis. Possible inhibition pathway is derived in terms of radical coupling mechanism. Under optimized conditions, the calibration plot showed a linear range up to 150 muM with a detection limit (S/N = 3) of 0.5 muM (i.e., 1.3 ng in 20 µL sample loop). The precision for 18 successive injection of 0.1 mM allopurinol showed a relative standard deviation of less than 2%. The proposed method is used to detect the amount of allopurinol in a commercially available pharmaceutical drug to show its potential use in real applications.
Ascorbic acid

"Flow Injection Analysis Of Ultratrace Sulfide At Low Potentials On Screen-printed Carbon Electrode Modified With Cinder/hexacyano Cobaltate Hybrid"
Electroanalysis 2002 Volume 14, Issue 7-8 Pages 513-518
Jyh-Myng Zen, Pei-Yan Chen, Annamalai Senthil Kumar

Abstract: Flow injection analysis (FIA) of ultratrace sulfide has been demonstrated on a screen-printed carbon electrode modified with industrially waste cinder/hexacyano cobaltate (CoHc) hybrid (designated as cinder/CoHcSPE) in pH 2 NH4Cl (0.1 M)/HCl solution at 0 mV (vs. Ag/AgCl). Hybridization of CoHc was achieved through bimetallic formation of Fe-III[Co-III(CN)(6)] in the *Fe-III[Co-III(CN)(6)] in the *Fe-enriched industrially waster cinder modifier. Possible mediated electrocatalytic oxidation of sulfide by higher oxidation state of Co in the hybrid-bimetallic complex is proposed for the system. Under the optimized conditions, the calibration plot is linear up to 2.08 µM with slope, regression coefficient, and detection limit (S/N=3) of 6.19 A/µM, 0.9985, and 12 nM, respectively. Interferences by direct electrochemical oxidation of easily oxidizable substances can be prevented due to the low detecting potential of the working system.

"Amperometric Enzyme Electrode For Hydrogen Peroxide Determination Prepared With Horseradish Peroxidase Immobilized In Polyvinylferrocenium (PVF+)"
Electroanalysis 2002 Volume 14, Issue 7-8 Pages 505-511
Mehtap G&uuml;ndogan-Paul, Haluk &Ouml;zy&ouml;r&uuml;k, Serdar S. &Ccedil;elebi, Attila Yildiz

Abstract: Steady state amperometric measurements of hydrogen peroxide in aqueous medium was performed by an enzyme electrode which was developed by electrostatic immobilization of the horseradish peroxidase, HRP, in Poly(vinyl ferrocenium perchlorate), PVF+ClO4, film, Amperometric measurements were performed at an applied potential of +0.7 V (vs. SCE). The effects of working temperature, enzyme concentration, film thickness and dissolved oxygen on the response of the electrode were elucidated. The responses of the PVF+E- electrode, PVF+ ClO4- coated electrode and uncoated Pt electrode were compared. The activation energy and the apparent Michaelis-Menten constant were calculated for enzyme electrode system. The linear working range, the sensitivity and the stability of the biosensor were also determined. Mechanisms for the operation of the electrode with and without immobilized enzyme in the polymer matrix are proposed.

"The Influence Of Diffusion Fluxes On The Detection Limit Of The Jalpaite Copper Ion-selective Electrode"
Electroanalysis 2002 Volume 14, Issue 7-8 Pages 493-498
Alberto Zirino, Roland De Marco, Ignacio Rivera, Bobby Pejcic

Abstract: It has been suggested that electrode dissolution and the concomitant saturation of the electrodes diffusion layer restricts the detection limit of the jalpaite Cu ion-selective electrode (ISE) to samples with total Cu levels above 10^-6 mol L-1 [1, 2]. This article will use rotating disk electrode (RDE) data for San Diego Bay seawater and Ficks law of diffusion to demonstrate that the static commercial Orion Cu ISE (employing a jalpaite membrane) produces a background level of contamination of (2.0±0.5) x 10^-8 mol L-1 total Cu, and the reduced thickness of the Orion Cu ISEs diffusion layer in the presence of hydrodynamic flow [e.g., at an RDE, or in continuous flow analysis (CFA)] lowers the background contamination of Cu to <10^-9 mol L-1. Furthermore, the RDE Cu ISE employing an electrode fabricated using jalpaite precipitated in 80% excess Na2S, so as to minimize the presence of occluded and leachable Cu2+ salts and extraneous phases such as silver sulfide [3 - 5], reveals an improvement in the lower limit of detection compared to the commercial Orion Cu ISE.
Calibration

"Differential Pulse Voltammetric Determination Of Trace Os(IV) At A Sol-gel-ceramic-carbon Powder-9-phenyl-3-fluorone Composite Electrode In Flow Systems"
Electroanalysis 2002 Volume 14, Issue 6 Pages 420-426
Soo Beng Khoo*, Ruidong Ye

Abstract: A composite electrode containing sol-gel-ceramic/carbon-powder/chemical-modifier as components was fabricated. This electrode was electrochemically viable and stable under both still and flow conditions. When the chemical modifier used was phenylfluorone, the composite electrode was useful for the sensitive and selective determination of Os(IV) under continuous flow and flow injection regimes. For these two modes, the detection limits were found to be 2.4 x 10^-9 M Os(IV) (S/N = 3) and 3.8 ng (500 µL injection of 3.98 x 10^-8 M Os(IV), S/N = 3), respectively. Selected substances were investigated for possible interferences. The developed method was utilized for the determination of Os(IV) in various backgrounds.

"Development Of Conducting Polymer Modified Electrodes For The Detection Of Phenol"
Electroanalysis 2002 Volume 14, Issue 5 Pages 325-332
W. Lu, G. G. Wallace, M. D. Imisides

Abstract: In this work, the feasibility of using conducting polymers to prevent electrode fouling caused by the oxidation of phenol has been investigated. The use of the conducting polymers, polyaniline and polypyrrole with a range of different counterions have been investigated. Electrode fouling was alleviated with polymers incorporating counterions containing hydrophilic groups. A significant improvement in performance was obtained using polypyrrole with o-aminobenzesulfonic acid incorporated. The analytical application of this polymer modified electrode as an amperometric sensor was investigated using flow injection analysis. Under flow conditions, a stable and reproducible response was obtained when a pulsed potential waveform was applied.

"Enzyme Based Amperometric Biosensors For Food Analysis"
Electroanalysis 2002 Volume 14, Issue 4 Pages 241-261
Mamas I. Prodromidis, Miltiades I. Karayannis

Abstract: This review introduces the principles of amperometric detection e.g. oxygen electrodes. hydrogen peroxide electrodes, NADH detection, mediators-aid detection, conductive organic salts and wiring electrodes. A short categorization and description of the materials commonly used for the construction of electrodes, e.g., platinum, glassy carbon, different types of graphite. screen-printed electrodes, rigid carbon-polymer biocomposites, zeolites, clays, and polymeric membranes is given. Approaches to construction of biosensors with respect to various strategies of enzyme immobilization, e.g.. physical binding, covalent binding, gel entrapment, electropolymerization, sol-gel techniques and self-assembled architectures are also presented. The requirements and problems for sensing in food industry, examples of enzyme electrodes, published in the literature during the last half-decade. commercial biosensors released into the market along with the current and modern instrumentation, are also presented.

"Electrocatalytic Oxidation And Flow Injection Amperometric Determination Of 5-hydroxytryptophan"
Electroanalysis 2002 Volume 14, Issue 3 Pages 231-234
Jamie L. Cohen, Justyna Widera, James A. Cox

Abstract: The oxidation of 5-hydroxytryptophan (5-HTPP) at a glassy carbon electrode was not suited for electroanalysis because of surface passivation. Both mixed-valence ruthenium oxide with cyano crosslinks (RuOx) and a pentaerythritol-based metallodendrimer with Ru(II)terpyridine units (Ru(II)Den) provided electrocatalytic oxidation without passivation. The former was used as an electrochemically deposited film on glassy carbon, and the latter was a component of a composite electrode with a sol-gel binder. Flow injection analysis with amperometric detection at constant applied potential yielded detection limits of 0.16 muM and 50 nM 5-HTPP with RuOx and Ru(II)Den catalysts, respectively.

"Direct Bioelectrocatalysis At Carbon Electrodes Modified With Quinohemoprotein Alcohol Dehydrogenase From Gluconobacter Sp. 33"
Electroanalysis 2002 Volume 14, Issue 1 Pages 43-49
J. Razumiene, M. Niculescu, A. Ramanavicius, V. Laurinavicius, E. Cs&ouml;regi

Abstract: A newly isolated, purified, and characterized PQQ-dependent alcohol dehydrogenase (a bacterial membrane-bound protein) was recently found to display a surprisingly large linear range and high selectivity towards ethanol when integrated into a conducting polymer network on a platinum electrode. These findings motivated us to study the enzyme when simply immobilized onto carbonaceous surfaces in order to establish its characteristics and suitability for sensor development, the sensor design being based on a direct-electron transfer pathway. Graphite rods and screen-printed electrodes were modified in two different ways, and were operated both in FIA and batch mode. The obtained biosensor characteristics were highly dependent on the sensor architecture, the highest sensitivity (179 mA M-1 cm-2) and lowest detection limit (1 muM) being obtained for screen-printed electrodes used in a batch mode. A mechanism of the observed direct electron transfer between the enzymes active center and the electrode is proposed.

"A Theoretical Model For Immobilized Enzyme Inhibition Biosensors"
Electroanalysis 2001 Volume 13, Issue 18 Pages 1528-1534
Shanqing Zhang, Huijun Zhao, Richard John

Abstract: The development and experimental verification of a theoretical model for immobilized enzyme inhibition biosensors is reported. The model predicts that the percentage of inhibited enzyme (I%), after exposure to air inhibitor, is linearly related to both die inhibitor concentration ([I](B)) and the square root of incubation time (t(1/2)): I% = Kt(1/2)[I](B) x 100 The model is based on diffusion limited inhibitor transport and takes into account the heterogeneous nature of enzyme inhibition that results from immobilization of an enzyme at the surface of a transducer. Experimental verification of the model A as achieved using an electrochemical (amperometric) acetylcholine sensor, The immobilized enzyme used in this study was acetylcholinesterase, while die organophosphorus pesticide. paraoxon, was employed as the inhibitor. A second enzyme, choline oxidase, was co-immobilized to facilitate electrochemical detection of the substrate. To satisfy the conditions required by the proposed model a specially designed biosensing device was fabricated employing a microdisk array as the transducer, Acetylcholinesterase (0.00025 units) and choline (1.0 units) were co-immobilized onto die array using a water-based polyurethane/polyethlene oxide colloidal dispersion matrix. A dialysis membrane was used as an active barrier to present fouling of the array and to restrict enzyme leaching. The device vas used for both batch and flow injection analysis and experimental results verifying the proposed model are presented using both modes.

"An Electrochemical In Vivo Flow-Injection System For Highly Selective And Sensitive Detection Of L-Glutamate Using Enzyme Reactor Involving Amplification"
Electroanalysis 2001 Volume 13, Issue 16 Pages 1361-1366
Toshio Yao*, Youko Nanjyo, Teruhisa Tanaka, Hirohito Nishino

Abstract: A bioelectrochemical in vivo flow-injection system with an on-line microdialysis sampling is proposed for the assay of the trace amounts of L-glutamate released from rat brain cells. The system includes a microdialysis probe, two immobilized enzyme reactors, a six-way autoinjector, and a poly(1,2-diaminobenzene) film-coated platinum electrode. In the first stage of the operation, the dialysate from the probe was delivered to the sample loop of the six-way autoinjector by perfusing Ringer's solution for 3 min at 2 L min-1. The calibration of the detection system including enzyme reactors was performed simultaneously. In the second stage, the dialysate in sample loop was automatically injected for 30 s into the flow-injection line and assayed. An L-glutamate oxidase/glutamate dehydrogenase coimmobilized reactor was used as an on-line amplifier based on the substrate recycling. To improve the substrate specificity of this reactor, acidic pretreatment and 6-diazo-5-oxo-L-norleucine treatment were done. The resulting enzyme reactor worked as a specific reactor of L-glutamateinvolving amplification (amplification factor was about 60 at a carrier flow-rate of 100 L min-1). The cycle was also initiated with 2-oxoglutarate, and so saccharopine dehydrogenase reactor was positioned in series before the amplifier reactor to remove 2-oxoglutarate. By the present method, the variations of L-glutamate level released from rat brain cells were assayed in vivo and also after continuous stimulation of KCl, to demonstrate the reliability of the system. Analytical speed was 20 dialysates h-1 and the detection limit was less than 0.5 M.

"Aluminum Speciation With Adsorptive Pyrocatechol Violet-Al(III) Complex By Derivative Adsorption Chronopotentiometry"
Electroanalysis 2001 Volume 13, Issue 15 Pages 1279-1286
Xianlong Wang, Shuping Bi, Ning Gan, Zongbo Wei

Abstract: An electrochemical procedure is proposed for the speciation of aluminum (At) by derivative adsorption chronopotentiometry on a hanging mercury drop electrode (HMDE) using pyrocatechol violet (PCV) as a complexing agent. Labile monomeric Al fraction (mainly inorganic Al) was determined at PH 4.9 (accumulation time 60 s, accumulation potential -0.45 V, PCV concentration 1.5 x 10^-6 mol L-1 and stripping current 5 muA), while total monomeric At fraction was determined at pH 8.2 (accumulation time 60 s, accumulation potential -0.50 V, PCV concentration 2.5 x 10^-6 mol L-1 and stripping current 5 muA). This sensitive and simple fractionation method was successfully applied to the speciation of Al in natural water samples. Five fractions were determined and measured: i) labile monomeric At (Ali); ii) total monomeric At (Ala) iii) acid reactive Al (Alr); iv) nonlabile monomeric At (Alo); v) acid soluble At (Als). The results were satisfactorily in agreement with those of the 8-hydroxyquinoline extraction/ion exchange method.

"Electrochemical Determination Of Chlorophenols At Microcylinder Poly(3-methylthiophene) Modified Electrodes Based On A Previous Chemical Oxidation Using Bis(trifluoroacetoxy)iodobenzene"
Electroanalysis 2001 Volume 13, Issue 15 Pages 1231-1236
L. Ag&uuml;&iacute;, B. Serra, P. Y&aacute;&ntilde;ez-Sede&ntilde;o, A. J. Reviejo, J. M. Pingarr&oacute;n*

Abstract: A sensitive electroanalytical method for the determination of chlorophenols (CPs) based on their chemical oxidation to the corresponding chlorobenzoquinones using bis(trifluoroacetoxy)iodobenzene (BTIB) is reported. The electrochemical monitoring of the chloro-benzoquinones is performed using cylindrical carbon fiber microelectrodes (CFMEs) modified with poly(3-methylthiophene) (P3MT) coatings. Variables involved in the oxidation of CPs by BTIB, such as the time needed for completion of the chemical oxidation, the influence of pH, of the supporting electrolyte concentration, and of the BTIB amount were optimized. Square-wave voltammetry at a P3MT-coated CFME allowed the obtention of detection limits of around 2.0 x 10^-7 mol L-1 for the different CPs. The amperometric detection of the CPs at P3MT-coated CFMEs was carried out under flow-injection conditions by using a flow-cell specially adapted for the use of microelectrodes. Taking into account the best signal-to-noise ratio, a potential of 0.20 V was selected for the amperometric detection. Under the optimized conditions, no evidence of modified microelectrode fouling was observed and no cleaning or regeneration pretreatment was needed when working with the same polymer modified microelectrode during the whole working day. The limits of detection obtained by FI with amperometric detection were close to 5 x 10^-8 mol L-1.

"A Glucose Biosensor Based On Electro-Enzyme Catalyzed Oxidation Of Glucose Using A HRP-GOD Layered Assembly"
Electroanalysis 2001 Volume 13, Issue 14 Pages 1198-1202
T. Ferri*, S. Maida, A. Poscia, R. Santucci

Abstract: The assembly and the characterization (by DC cyclic voltammetry and flow injection analysis (FIA) mode) of a bienzymatic biosensor for glucose is described. The biosensor is constituted by a glucose oxidase (GOD)-entrapping cellulose triacetate membrane, layered onto a polymeric membrane (polystyrene cross-linked with 1 % divinyl benzene functionalized with tributylmethyl phosphonium chloride (TBMPC)) embedding horseradish peroxidase (HRP), previously blocked onto a pyrolitic graphite electrode (PGE). Under flowing conditions, the biosensor, which gives place to direct, unmediated electron-transfer, responds linearly to the glucose up to 5.0 mM with a precison always better than 5 %, and the detection limit was 0.07 mM. The influence of different experimental parameters, like temperature, flow rate, applied potential, interferents, etc., has been evaluated. For what concerns the potential interferences, no interfering species, as ascorbic acid, urea, etc., affects the biosensor response. The biosensor, characterized by an operational stability of at least twenty days, has been successfully tested on real samples.

"Microelectrodes Modified With [MIII(bpy)3](ClO4)3 (M = Co And Fe) As Analytical Sensors For Fullerenes In Flow Injection Analysis"
Electroanalysis 2001 Volume 13, Issue 14 Pages 1185-1190
Marta E. Plonska, Piotr Diakowski, Tadeusz Krogulec, Krzysztof Winkler

Abstract: Catalytic electroreduction of fullerene (C60) at Au or Pt microelectrodes covered with [MIII(bpy)3](ClO4)3 (M = Co and Fe, and bpy = 2,2?-bipyridine) was investigated. Under constant potential oxidation in acetonitrile/toluene (1:4, v/v) solution containing [MII(bpy)3]2+ complexes and (n-Bu)4NClO4 as a supporting electrolyte, the microelectrodes were modified with electrochemically inactive [MIII(bpy)3](ClO4)3 films. The chemical reduction of electrochemically formed films by C60- results in enhancement of fullerene reduction current enabling thus for sensing of C60. Analytical performance of electrodes modified with [Co(II)I(bpy)3](ClO4)3 was better than those covered with [Fe(III)(bpy)3](ClO4)3. Microelectrodes modified with [Co(II)I(bpy)3](ClO4)3 were used to quantify the fullerene concentration in flow injection analysis. In the proposed analytical procedure the solution containing both the [Co(II)(bpy)3]2+ complex and the C60 analyte was injected to the flowing stream of an acetonitrile/toluene (1:4, v/v) mixture containing (n-Bu)4NClO4. The triangular potential waveform was applied to the gold microelectrode. During the positively going potential scan the electrode was covered by an electrochemically inactive [Co(II)I(bpy)3](ClO4)3 layer. In the cathodic scan, the catalytic current of C60 reduction was recorded. A dependence of a current signal of catalytic C60 reduction on fullerene concentration was linear in a concentration range 5 x 10^-7 to 2 x 10^-5 mol L-1. Reproducibility of the electrode response under FIA conditions was good.

"Flow Injection Chemiluminescence Determination Of Captopril With In Situ Electrogenerated Mn3+ As The Oxidant"
Electroanalysis 2001 Volume 13, Issue 12 Pages 1046-1050
Xingwang Zheng, Zhujun Zhang, Baoxin Li

Abstract: By designing a novel flow-through electrolytic cell, a new flow-injection electrogenerated chemiluminescence method for the determination of captopril is described. It is based on the direct chemiluminescence oxidation of captopril by nascent Mn3+ which was in situ electrogenerated on the near surface of the platinum flake electrode by electrochemical oxidizing MnSO4 in sulfuric acid medium. The proposed procedure has a linear application range of 3.0 x 10^-7-1.0 x 10^-4 mol/L for captopril (r=0.9998) and with a detection limit of 8.0 x 10^-8 mol/L original concentration. Designing of the flow-through electrolytic cell as well as some experimental conditions for the determination of captopril are optimized and the possible reaction mechanism is also discussed. The method was successfully used for the determination of captopril in a pharmaceutical preparation.

"Prussian Blue And Its Analogues: Electrochemistry And Analytical Applications"
Electroanalysis 2001 Volume 13, Issue 10 Pages 813-819
Arkady A. Karyakin

Abstract: This article reviews fundamental aspects of deposition, structure and electrochemistry of Prussian Blue and its analogues. Special attention is given to the metal hexacyanoferrates with potential analytical applications. Prussian Blue and its analogues as advanced sensing materials for nonelectroactive ions are discussed. In contrast to common smart materials, the sensitivity and selectivity of metal hexacyanoferrates to such ions is provided by thermodynamic background. Prussian Blue itself is recognized as the most advantageous low-potential transducer for hydrogen peroxide over all known systems. Both high sensitivity (ca. 1 A M-1 cm-2) and selectivity in relation to oxygen reduction are more than three orders of magnitude higher, than for platinum electrodes. Biosensors based on different transducing principles containing enzymes oxidases are compared, and the devices operated due to hydrogen peroxide detection with the Prussian Blue based transducer are shown to be the most advantageous ones. The future prospects of chemical and biological sensors based on metal hexacyanoferrates are outlined.

"Long-optical-path Thin-layer Spectroelectrochemical Flow Cell With Inexpensive Gold Electrodes"
Electroanalysis 2001 Volume 13, Issue 8-9 Pages 681-685
Daniela Daniel, Ivano G. R. Gutz

Abstract: A novel long-optical-path thin-layer spectroelectrochemical cell for flow systems is described and its suitability for in situ UV-visible applications, demonstrated. Gold electrodes with flat surface are simply cut from standard recordable CDs of the gold sputtered type. After removal of the protecting polymer layer, the area of the working and auxiliary coplanar electrodes is delineated by scraping off the gold layer. A set of twin electrodes is placed face to face within any standard spectrophotometric cuvette with 1.0 cm optical path. The sample is introduced with a syringe or peristaltic pump and reaches the bottom of the working electrodes through a PTFE tube. Evaluation was done with o-tolidine in acidic medium as a model system, and gave good results under stationary conditions and in the FIA mode. The appropriateness of the tell for flow operation including FlA, good potential control, simplicity of construction and maintenance, easy adaptability to existing instrumentation and a cost lower than any other proposed model are advantages of the innovative cell design.

"Flow Detection Of UV Radiation-induced DNA Damage At A Polypyrrole-modified Electrode"
Electroanalysis 2001 Volume 13, Issue 7 Pages 537-540
Joseph Wang, Mian Jiang, Abdel-Nasser Kawde

Abstract: A new electrochemical protocol for the detection of radiation-induced DNA damage, based on the coupling of a conducting-polymer detector and a flow injection system, is described. Changes in the interaction of DNA molecules with polypyrrole (PPy) films, after exposure to ultraviolet radiation, are exploited for generating the damage-sensitive current signals. Factors influencing the response of the flow detector, including the irradiation time or distance, are discussed. Injection rates of 30-60 per hour are obtainable in connection to 20 µL sample volumes and nanogram quantities of plasmid and chromosomal DNA. The new modified-electrode/flow-injection protocol offers great promise for detecting DNA damage in a faster and simpler manner compared to the common use of ordinary electrodes in batch systems. It also adds a new dimension of information based on the interfacial properties of damaged DNA at conducting-polymer/solution interfaces. The PPy-coated glassy-carbon electrode thus represents a useful addition to the arsenal of electrochemical tools for detecting DNA damage.

"A New Potentionmetric Photocurable Membrane Selective To Anionic Surfactants"
Electroanalysis 2001 Volume 13, Issue 6 Pages 471-476
Joan S&agrave;nchez, Manuel del Valle

Abstract: The preparation of photocurable polymer membranes selective to anionic surfactants and their application to all-solid state ion-selective electrodes ar e reported. A preliminary trial employing CHEMFET devices is also shown. Membranes are based on a urethane-acrylate polymer, and use 2-cyanophenyl octyl ether (CPOE), a plasticizer compatible with the photocuring process. These membranes are highly selective to the anionic surfactants assayed while common inorganic anions did not interfere. An optimization methodology is proposed for their formulation, suited to the final application. Several membrane compositions were obtained using between 44 and 48% (w/w) CPOE. A membrane with a general-purpose formulation is fully characterized and we show calibration results for anionic surfactants such as dodecylbenzenesulfonate (DBS-), tetrapropylenebenzenesulfonate and dodecylsulfate, or cationic surfactants such as Hyamine 1622 and cetyltrimethylammonium ion. With the primary ion DBS- we verified a 58.1 mV/dec sensitivity, a linear response between L x 10^-3 M and 3 x 10^-6 M, a detection limit corresponding to 0.26 ppm DBS- (7.9 x 10^-7 M) and a slope precision of 2.8 % RSD between days.

"Effect Of DNA On The Peroxidase Based Biosensor For Phenol Determination In Waste Waters"
Electroanalysis 2001 Volume 13, Issue 6 Pages 445-450
Simone S. Rosatto, Graciliano de Oliveira Neto, Lauro T. Kubota

Abstract: The influence of different additives, like bovine serum albumin (BSA), polyethylenimine (PEI) and DNA, on the sensitivity and operational stability of a phenol biosensor based on peroxidase immobilized on silica-titanium and mixed in carbon was studied. The best results were found with electrodes containing DNA in the paste, although with BSA better results were obtained, compared to the electrode without additives. The response of biosensor incorporating DNA decayed ~50 % after 3 to ii days of use, but it then remained constant for 25 days of daily use, when stored in a phosphate buffer solution under refrigeration between experiments. Original performance was recovered by simply substituting the used paste for a new portion of stock paste. The high sensitivity for phenol due to the immobilization of peroxidase on silica-titanium and the increase of stability of the biosensor provided by DNA addition were essential for the successful determination of phenol in real samples, with an average of 104.5 % recovery.

"Interference Elimination In Glutamate Monitoring With Chip Integrated Enzyme Microreactors"
Electroanalysis 2001 Volume 13, Issue 6 Pages 425-431
A. Collins, E. Mikeladze, M. Bengtsson, M. Kokaia, T. Laurell, E. Cs&ouml;regi

Abstract: On-chip enzyme reactors are often used in medical/pharmaceutical analysis due to their inherent advantages, such as high sample throughput, low reagent consumption, stability, reproducibility and low cost. The present work describes a different application of such microreactors, namely, elimination of interfering ascorbate signals in glutamate monitoring using ascorbate oxidase modified silicon chip microreactors of different sizes (5.3 and 0.95 µL). Glutamate was monitored with a previously developed redox hydrogel integrated bienzyme electrode, based on coupled glutamate oxidase and horseradish peroxidase, inserted in a miniaturized flow cell operated at -50 mV (vs. Ag/AgCl). The developed on-line analysis system was characterized with regard to dilution effects, detection limit, response time and interference ability using model solutions and real samples. Off-line in vivo glutamate measurements could be made by injecting rat brain microdialysate samples collected before and after KCl stimulation without any interference of ascorbate, I Within the studied flow rate range (2-25 µL/min), 1 mM and 200 muM ascorbate could he totally eliminated using the larger and the mailer microreactor, respectively.

"Glucose-sensing Electrode Based On Glucose Oxidase-attached Polyion Complex Membrane Containing Peroxidase And Ferrocene"
Electroanalysis 2001 Volume 13, Issue 5 Pages 380-383
Soichi Yabuki, Fumio Mizutani, Yoshiki Hirata

Abstract: A glucose oxidase (GOD)-attached polyion complex membrane containing peroxidase (POD) and ferrocene was prepared by two steps on a glassy carbon electrode. First, a polyion complex membrane containing POD and ferrocene was prepared: a poly-L-lysine solution, a POD solution, a ferrocene dispersion and a poly(styrenesulfonate) solution were successively dropped on an electrode, and the electrode was allowed to dry. Then GOD was attached by the use of glutaraldehyde: GOD and glutaraldehyde solutions were dropped on the membrane. and the electrode was dried. Current response to glucose for the enzyme electrode was measured at a potential of -0.2 V (vs. Ag/AgCl). The 100 % response time was ~20 s. The current was proportional to the glucose concentration up to 0.1 mM. The lower detection limit was 1 muM (signal-to-noise ratio. S/N = 5). The enzyme electrode was used for the glucose measurements in beverages. The results obtained agreed well with those obtained by Boehringer F-kit method. The electrode would be useful as a glucose biosensor for beverages.
Polymer

"Mitochondria-based Amperometric Biosensor For The Determination Of L-glutamic Acid"
Electroanalysis 2001 Volume 13, Issue 3 Pages 243-245
S.T. Girousi, A.A. Pantazaki, A.N. Voulgaropoulos

Abstract: A mitochondria based amperometric biosensor was developed for the determination of L-glutamic acid. The biosensor was characterized using hexacyanoferrate(III) as the electrochemical mediator. The electrochemical behavior of the redox couple hexacyanoferrate(II)/(III) was improved by incorporating octadecylamine into the enzyme modified carbon paste. L-Glutamic acid was detected at +0.35 V Linearity was observed in the range 0.4-10 mM of L-glutamic acid (sensitivity 0.189 muA/mM, correlation coefficient 0.997) and in the range 10^-100 mM (sensitivity 0.021 muA/mM. correlation coefficient 0.958). The detection limit was 0.1 mM. The electrode maintains 60% of its activity after 10 days of use. The bioelectrode was used for the determination of L-glutamate in chicken cube samples.

"Design Of A Multilayer Cholesterol Amperometric Biosensor For Preparation And Use In Flow Systems"
Electroanalysis 2001 Volume 13, Issue 3 Pages 229-235
Juan-Carlos Vidal, Esperanza Garc&iacute;a-Ruiz, Juan-Ram&oacute;n Castillo

Abstract: A cholesterol amperometric biosensor based on a multilayer configuration with an initial platinized layer electrodeposited on the electrode surface and two sequentially electrosynthesized polymer layers was developed. The polymer bilayer was formed by an inner polypyrrole layer, in which cholesterol oxidase was entrapped and an outer layer of poly(o-phenylenediamine). All biosensor preparation steps and the determination of the substrate were carried out in a Row system, which permitted acceptable reproducibility of the fabrication process of each biosensor. The resulting biosensor, with a detection process based on the electrochemical oxidation at +0.5 V(vs. Ag/AgCl) of the enzymatically produced hydrogen peroxide, displayed high efficacy in the signal generation process (above 97 %) and had a stable response period of approximately one month. The presence of the two polymer layers had no incidence on the response time (t(95) = 8 s) and sensitivity and the detection limit are 62 nA mM-1 and 12 muM, respectively The characteristics of the biosensor were compared to those of other biosensors with a more simple configuration, which confirmed the considerable advantages of the biosensor developed. The combined permselective properties of the two polymer layers permitted satisfactory determination of the cholesterol content in reference synthetic serum samples.
Enzyme Membrane

"Evaluation Of A Four Sensor Array Used In A Wall-jet Configured Flow Cell For Plow Injection Potentiometry"
Electroanalysis 2001 Volume 13, Issue 2 Pages 161-163
Lucy Tina Dimitrakopoulos, Telis Dimitrakopoulos

Abstract: Photo-cured calcium, potassium, and nitrate ion-selective electrodes and Ag/AgCl wire as a chloride electrode have been integrated into a sensor array that is suitable for FIP measurements in a wall-jet flow cell. Each sensor in the electrode-array exhibited near-Nemstian response over a log-linear range between 0.1 mM and 10 mM and detection limits of 0.01 mM in the flow injection potentiometric mode. The four coated wire electrodes were used simultaneously in the flow injection mode to determine their respective determinand in various water samples and the results were in good agreement with standard analytical methods.
pH

"Anodic Oxidation Of Nitrite At A Molybdenum Oxide Layer"
Electroanalysis 2001 Volume 13, Issue 2 Pages 155-160
Jos&eacute; R.C. Rocha, Lu&iacute;s Kosminsky, Thiago R.L.C. Paix&atilde;o, Mauro Bertotti

Abstract: The anodic oxidation of nitrite at a glassy carbon surface modified by a molybdenum oxide layer electrochemically deposited is discussed. The results demonstrated that at certain thickness values the film is permeable to small substrates like iodide and nitrite. On the other hand, at anhydrous films (prepared by vacuum evaporation) no electrochemical response for nitrite was observed in experiments performed in a CH3CN solution, confirming the relationship between the porosity of the film and its water content. Voltammetric curves recorded in alkaline solutions showed an enhanced response for the oxidation of nitrite when the electrode surface is modified with the MoO3 film, which is nonconductive at the working potential range. The current enhancement is probably associated with an entrapment of NO2 (electrogenerated in a first step) at the electrode/film interface, the MoO3 sites transferring an O-atom in a further step. The modified electrode was used as an amperometric sensor for nitrite in a flow injection configuration, the method being applicable in the range 5 to 1000 muM at a potential of 1.0 V. The repeatability of the analysis is around 3% and the lower limit of detection is 1 muM. The method was used in the determination of nitrite in sausage samples with a recovery of 104%.

"On-line Analysis Of Mercury By Sequential Injection Stripping Analysis (SISA) Using A Chemically Modified Electrode"
Electroanalysis 2001 Volume 13, Issue 1 Pages 79-82
Iva Turyan, Thomas Erichsen, Wolfgang Schuhmann, Daniel Mandler

Abstract: A highly flexible, automatic sequential-injection stripping analysis (SISA) system has been developed and applied For monitoring the levels of mercury in aqueous solutions using a chemically modified electrode. The preparation of the modified electrode comprises spin coating of an ethanolic solution of poly(4-vinylpyridine) and Kryptofix-222 onto a glassy carbon electrode (GCE) followed by cross-linking the polymer. The analysis is based on the anodic stripping voltammetry of mercury using differential pulse voltammetry. A sequence of 36 operations was needed to complete a full cycle of cleaning, calibration and analysis.

"End-column Electrochemical Detection For Capillary Electrophoresis"
Electroanalysis 2000 Volume 12, Issue 17 Pages 1349-1355
Frank-Michael Matysik

Abstract: Amperometric and voltammetric techniques are very attractive for detection in capillary electrophoresis (CE). The low limits of detection attainable with capillary electrophoresis-electrochemical detection (CE-ED) are a definite advantage over the widely used on-column UV detection for CE. To fully exploit the potential of CE-ED and to make it accessible to the non-specialist, robust and user-friendly detector devices have to be developed. This article reviews recent advances in the field of end-column CE-ED which can be operated without the implementation of an electrical-field decoupler. Emphasis is given on the discussion of methodical aspects and on the design of decoupler-free detector configurations that are promising to enhance the practicality of CE-ED.

"Disposable Chemical Oxygen Demand Sensor Using A Microfabricated Clark-type Oxygen Electrode With A TiO2 Suspension Solution"
Electroanalysis 2000 Volume 12, Issue 16 Pages 1334-1338
Kyong-Hoon Lee, Yoon-Chang Kim, Hiroaki Suzuki, Kazunori Ikebukuro, Kazuto Hashimoto, Isao Karube

Abstract: A disposable chemical oxygen demand (COD) sensor was constructed using a microfabricated Clark-type oxygen electrode and titanium dioxide (TiO2) fine particles suspended in a sample solution. Under UV irradiation, a decrease in the dissolved oxygen in the sample was correlated to COD, a parameter representing the organic concentration of the sample. The sensor performance was evaluated using artificial and real water samples from lakes in Japan. The response time of the sensor was approximately 3-4 minutes with a detection limit of 0.118 ppm.

"Epoxy Matrix Membrane Potentiometric Sensor Based On Zirconium Titanium Phosphate Ion Exchanger For Flow Injection Analysis Of Nitrite"
Electroanalysis 2000 Volume 12, Issue 16 Pages 1312-1317
Saad S. M. Hassan, Sayed A. Marei, I. H. Badr, H. A. Arida

Abstract: Preparation, characterization, origin of response and applications of a potentiometric sensor based on the use of a zirconium titanium phosphate (ZTP)-epoxy membrane are described. Zirconium titanium phosphate (ZTP) cationic exchanger embedded in an epoxy matrix is converted into a hydrated zirconium oxide anion exchanger which responds to many anionic species. A sensor based on this exchanger exhibits near-Nernstian response for nitrite and other anions over the concentration range 10^-1 - 10^-5 M. Under optimized conditions, the gas dialyzer/flow injection system provides a throughput of ~60 samples per hour with a high selectivity for nitrite ion over most common anions and acidic gas releasing species. Determination of nitrite at levels as low as 5 x 10^-4 M or less in the presence of sulfite and sulfide ions is performed by using a modified carrier buffer stream (10^-2 M MES, pH 5.5 containing formaldehyde and Pb2+). Significant advantages are offered by the ZTP-epoxy membrane based sensor including a long lifetime ( >2 years), excellent stability and reproducibility (ca. 1 mV), fast response time ( < 30 s), wide pH working range (pH 4.5-8), low detection limit (4 x 10^-5 M) and high thermal stability (up to 80°C).
Selectivity

"A Simple FIA-system For Simultaneous Measurements Of Glucose And Lactate With Amperometric Detection"
Electroanalysis 2000 Volume 12, Issue 16 Pages 1304-1311
Sayed A. M. Marzouk, Hossam E. M. Sayour, Ahmed M. Ragab, Wayne E. Cascio, Saad S. M. Hassan

Abstract: A flow injection system for the simultaneous amperometric determination of glucose and lactate is described. Glucose oxidase and lactate oxidase were immobilized separately, into two-parallel immobilized enzyme reactors (IERs). The enzymatically produced hydrogen peroxide was detected by anodic amperometry at platinum electrodes coated with an electropolymeric-permselective layer of m-phenylenediamine to enhance the selectivity of H2O2 detection. The configuration of the how system was designed to give a response output in the form of a train of two successive peaks. The heights of these two peaks were directly proportional to the concentration levels of glucose and lactate in the sample, respectively. The presented flow system proved to offer the advantages of i) simplicity, ii) operational stability, up to 3 months, iii) simultaneous determination of glucose and lactate using a single 20 µL sample injection iv) insensitivity of the signal of a given component by wide variations in the concentration of the second component, v) high sample throughput, more than 50 samples/hour, vi) high accuracy and precision, and vii) a reasonable dynamic range of about two-orders of magnitude. The reliability of the present system was assessed by measuring glucose and lactate simultaneously in several samples of blood plasma, urine and dairy products. The obtained results were in good agreement with those obtained by standard spectrophotometric methods.
Glucose

"An Enzyme Electrode For Extended Linearity Citrate Measurements Based On Modified Polymeric Membranes"
Electroanalysis 2000 Volume 12, Issue 14 Pages 1118-1123
Andrew Maines, Mamas I. Prodromidis, Stella M. Tzouwara-Karayanni, Miltiades I. Karayannis, David Ashworth, Pankaj Vadgama

Abstract: Pyruvate oxidase (POD), oxaloacetate decarboxylase (AOCD), and citrate lyase (CL) were coimmobilized (or immobilized separately) in a series of polymeric membranes for the construction of amperometric bisensors of pyruvic, oxaloacetic, or citric acid in concentrated samples. For oxaloacetic acid, POD, and OACD were coimmobilized on dialysis membranes and were used in a multimembrane configuration with an inner spin-coated cellulose acetate (CA) membrane modified with isopropyl myristate (IPM) and an outer diffusion restricted membrane of cellulose acetate modified with a cationic surfactant. These membranes were also tested in a POD laminate containing the cofactors FAD and TPP for monitoring the response stability with duration of exposure to an external electrolyte and found to be effective in reagentless mode, with good pyruvate response stability over 3 h without compromise of signal size. Coimmobilization of POD/OACD and CL on different types of high protein binding membrane such as mixed cellulose ester (HA) was investigated. The relative optimum concentrations of several activators (divalent cations) and cofactors such as FAD and thiamine pyrophosphate (TPP) were investigated with the probe assembled as a pyruvate biosensor. An extended linearity up to 100 mM citric acid was achieved.
Detector

"BHA And TBHQ Quantification In Cosmetic Samples"
Electroanalysis 2000 Volume 12, Issue 13 Pages 1074-1076
Carlos Diego Garc&iacute;a, Patricia In&eacute;s Ortiz

Abstract: An amperometric flow injection method for the determination of the antioxidants BHA, TBHQ and a mixture of them, using a 4-hydroxybenzaldehyde/formaldehyde polymer modified electrode is proposed. The procedure is based on the electrochemical oxidation in phosphate buffer solution (pH 7.2). Different analytical parameters and electrode stability were analyzed to obtain the best electrode performance, being the optimal conditions: working potentials 0.200 V and 0.700 V and flow rate 0.74 mL min-1. The proposed method was used for antioxidants quantification in a cosmetic sun tanning lotion, without any previous sample treatment and mean recoveries of 104% were obtained. Interferences from other antioxidants (BHT and PG) were also analyzed and in all the cases, no synergic behavior was observed.

"Portable Immunosensor For The Fast Amperometric Detection Of Anti-hantavirus Antibodies"
Electroanalysis 2000 Volume 12, Issue 13 Pages 1034-1038
Srinivas Vetcha, Ihab Abdel-Hamid, Plamen Atanasov, Dmitri Ivnitski, Ebtisam Wilkins, Brian Hjelle

Abstract: An amperometric immunosensor based on a recombinant nucleocapsid antigen has been developed for fast determination of antibodies against Sin Nombre (SN) virus in human blood serum. This approach combines the advantages of utilization of highly dispersed immunosorbent, with highly sensitive electrochemical detection of enzyme-marker, and flow injection scheme of immunoassay. A main benefit of recombinant nucleocapsid antigen is that antigen preparation and standardization is easy. The complete immunoassay can be performed in 24 minutes. The short overall assay time could be a major advantage in the field of diagnostic screening of infectious diseases in mobile laboratories and small hospitals. The immunosensor has been successfully used in the determination of anti-Hantavirus IgG in human blood plasma and is easily adaptable for the detection of other types of viral infections.

"Virtual Plume"
Electroanalysis 2000 Volume 12, Issue 12 Pages 974-979
Timo Kikas, Hiroshi Ishida, Philip J. W. Roberts, Donald R. Webster, Jiri Janata

Abstract: A bench-top model of a chemical plume in a turbulent flow, a Virtual Plume, was built to simulate the behavior of a turbulent chemical plume. It is based on an eight-channel FIA/SIA system and an array of eight amperometric sensors. A plug of sample solution was delivered to me sensors after passing through delay and dispersion elements. Adjusting these two elements enabled us to simulate the rime-concentration profile at any arbitrary point in the plume. It has been shown that an eight-channel system can simulate an arbitrary sensor array positioned in a turbulent plume. Preliminary correlation of the shape of the peaks obtained in the VP with those recorded using planar laser-induced fluorescence in a turbulent flow shows the value of this approach.
Turbulent flow

"Study Of The Reduction Of 1-(2 -pyridylazo)-2-naphthol In Ethanol-water Solutions"
Electroanalysis 2000 Volume 12, Issue 11 Pages 841-845
Spas D. Kolev, Lilibeth dlC. Coo, Terence J. Cardwell, Robert W. Cattrall

Abstract: The reduction of the azo dye 1-(2-pyridylazo)-2-naphthol (PAN) to 1-(2-pyridylhydrazino)-2-naphthol in ethanol-water solutions at a glassy carbon electrode was studied chronoamperometrically. A mathematical model taking into account the three dimensional diffusion of these two species and the disproportionation reaction of 1-(2-pyridylhydrazino)-2-naphthol was developed and fitted to the experimental chronoamperograms. In this way the value of the kinetic rate constant of the disproportionation reaction was determined as 0.090 s-1, in ethanol-water solutions containing 40, 80, and 100% (v/v) ethanol, respectively It was found also that electrons were involved in the reduction of the azo group. The value of the PAN diffusion coefficient used in the model calculations was determined earlier by flow injection analysis (FIA). The combination of FIA and chronoamperometry offers new possibilities in studying electrode reactions.

"Flow Injection Monitoring Of Aflatoxin M-1 In Cheese Using Filter-supported Bilayer Lipid Membranes With Incorporated DNA"
Electroanalysis 2000 Volume 12, Issue 10 Pages 747-751
Christina G. Siontorou, Vangelis G. Andreou, Dimitrios P. Nikolelis, Ulrich J. Krull

Abstract: This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring of aflatoxin M-1 (AFM(1)) in cheese samples. Stabilized filter-supported bilayer lipid membranes (BLMs) were used as detectors Single stranded DNA oligomers terminated with alkyl chains (dT(20)-C-16) were incorporated into the membranes to control surface electrostatic properties. The incorporation of dT(20)-C-16 in BLMs lowered the detection limit for the detection of this toxin by one to four orders of magnitude as compared with the detection limit obtained in the absence of DNA. Therefore, it is now possible to continuously monitor this toxin at concentrations that approached those that could be of interest as set by the U.S. Food and Drug Administration and most European countries. The work described herein takes a significant step towards development of a detector of greater practical potential by demonstrating that the incorporation of C-16-ssDNA into lipid membranes results in a combination of properties that provides for a much more sensitive and robust detection system. Injections of AFM(1) were made into flowing streams of a 0.1 M KCI electrolyte solution, and a transient current signal with duration of seconds reproducibly appeared in about 12 s after exposure of the detector element to the toxin. The magnitude of this signal was linearly related to the concentration of AFM(1) with detection limits at subnanomolar level. The effect of interferents such as proteins and lipids was investigated. It was determined that interferences from proteins could be eliminated by adjustment of the flow rate of the carrier electrolyte solution. The technique was applied for the rapid flow injection determination of aflatoxin MI in cheese samples. AFM(1) could be determined in continuous flowing systems with a rate of at least 3 samples min-1. Repetitive cycles of injection of AFM(1) have shown no signal degradation during each cycle for experiments that attempted over 30 cycles of detection.
Bilayer lipid membranes Extraction

"Determination Of Traces Of Uranium In Environmental Samples Using A Flow Injection System With Amperometric Catalytic Detection"
Electroanalysis 2000 Volume 12, Issue 10 Pages 742-746
Marco A. S. Aguiar, Karem S. G. Marquez, Ivano G. R. Gutz

Abstract: A new method for flow injection analysis (FIA) of traces of uranium by catalytic amperometric detection in nitrate medium is described. Interfering oxygen was removed by in-line degassing. A simple adapter was designed to afford FIA with batch cells comprising a hanging mercury drop electrode. The carrier electrolyte consisted of 10 mM LiNO3 and the electrolyte for the samples was 10 mM HNO3 + 10 mM LiNO3. The method is simple, rapid (up to 60 injections/h) and precise (RSD = 1.0% for n = 10 and C-U = 80 nM), presenting a LD of 13 pg of U or 3 nM (3 SD). Dissolution of solid samples (rock and soil) was abbreviated by employing a mixture of nitric and hydrofluoric acids in microwave heated closed vessels, followed by liquid-liquid extraction with TBP. Analysis of reference materials and intercomparison with other techniques gave very favorable results.

"Advances In The Microfabrication Of Electrochemical Sensors And Systems"
Electroanalysis 2000 Volume 12, Issue 9 Pages 703-715
Hiroaki Suzuki

Abstract: Technologies to microfabricate electrochemical sensors and systems are rapidly advancing and win surely have an impact on critical fields such as medicine, environment, and information processing. It is a good opportunity to review the state of the art and trends in the technologies developed in this field during the last two decades of the 20th century and prepare for the coming decades. Here, developed electrochemical microsensors and microsystems will be reviewed in terms of techniques and performance along with the problems left as issues for the next century.

"Amperometric Biosensor For Glutathione Based On Osmium-polyvinylpyridine Gel Polymer And Glutathione Sulfhydryl Oxidase"
Electroanalysis 2000 Volume 12, Issue 8 Pages 577-582
Lanqun Mao, Katsunobu Yamamoto

Abstract: A new amperometric biosensor based on glutathione sulfhydryl oxidase (GSH-SOx) and osmium-polyvinylpyridine gel polymer (Os-gel-HRP) bilayer film modified glassy carbon (GC) electrode was demonstrated for glutathione (GSH) and glutathione disulfide (GSSG). Os-gel-HRP was applied at glassy carbon (GC) electrode with a surface coverage of 7.1 µL/cm2 to sense hydrogen peroxide based on horseradish peroxide (HRP) catalytic reaction mediated by osmium. GSH-SOx was immobilized at Os-gel-HRP cast coated GC electrode with an approximate surface coverage of 7 U/cm2 by cross-linking with BAS-GSH-SOx in glutaraldehyde vapor for 5 min. The resultant bienzyme-based sensor was tested toward GSH and GSSG with techniques of cyclic voltammetry (CV), flow cell amperometry and flow injection analysis (FIA). The sensor was polarized at 0.0 V (versus Ag/AgCl, 3 M KCl) electrode for the detection of GSH and GSSG in a flow system at a flow rate of 6 µL/min. Linear response to GSH and GSSG in a concentration range from 1 µM to 200 µM and 2 µM to 120 µM was obtained at the sensor with a sensitivity of 1.195 nA/µM and 0.60 nA/µM for GSH and GSSG, respectively. The dependence of current response on pH value of the buffer and operating potential was also tested and optimized.
Derivatization

"Determination Of Buprenorphine In Pharmaceuticals And Human Urine By Adsorptive Stripping Voltammetry In Batch And Flow Systems"
Electroanalysis 2000 Volume 12, Issue 7 Pages 483-489
M. Angeles Garc&iacute;a-Fern&aacute;ndez, M. Teresa Fern&aacute;ndez-Abedul, Agust&iacute;n Costa-Garc&iacute;a

Abstract: The adsorption of buprenorphine on carbon paste electrodes has been studied by cyclic (CV) and differential pulse voltammetry (DPV). By applying a simple electrode pretreatment good reproducibility of the current signal is obtained (RSD=0.85 %, n=6 in CV and RSD=0. 35 %, n=6 in DPV for a 5.0 x 10^-7 M buprenorphine concentration in BR buffer pH 9.0). These methods permit a very sensitive (LD=2.0 x 10^-8 M) and selective determination. They were applied to the quantitation of buprenorphine in human urine coming from subjects following buprenorphine treatment. The methodology was coupled to a flow system incorporating a thin-layer flow cell. A linear response was obtained in the concentration range comprised between 1.0 x 10^-8 and 8.0 x 10^-7 M. The application to the determination of this molecule in pharmaceuticals (vials and tablets) and human urine without any sample pretreatment is studied.

"Immobilized Ionophore Calcium Ion Sensor Modified By Montmorillonite"
Electroanalysis 2000 Volume 12, Issue 6 Pages 468-470
Shih-Han Wang, Tse-Chuan Chou

Abstract: The effect of montmorillonite on the preparation of a calcium ion electrode was studied by combining and immobilization of ionophore and montmorillonite into a polymer membrane. Two types of electrodes to detect calcium ion concentrations were also compared. The results indicated that the montmorillonite-modified electrode exhibited higher performance than that without montmorillonite. The relationship between the potential and calcium ion concentration was obtained and the testing range of calcium ion concentration was from 4 x 10^-6 - 10^-1 M. The selectivity, reproducibility, and stability of modified electrodes with montmorillonite were better than electrode without montmorillonite. The optimal amount of the montmorillonite was 24.8 wt.%.

"Flow Injection Method For Preconcentration And Polarographic Determination Of Copper In Water"
Electroanalysis 2000 Volume 12, Issue 5 Pages 390-393
Pablo Richter, M. In&eacute;s Toral, Pablo Jaque

Abstract: The analytical application of a simple polarographic Row through cell, which was previously designed for the continuous polarographic analysis of organic compounds in pharmaceuticals and urine, is proposed in this work for the determination of copper in diluted water samples. The cell contains a conventional dropping mercury electrode (DME), a mercury pool and a platinum wire as the working, reference and counter electrodes, respectively Enrichment of the analyte, previous to the polarographic continuous determination. was necessary and was achieved by using a microcolumn containing Chelex-100, located in the loop of the injection valve. The Row through detector can be used either amperometrically, under continuous Row operation, or voltammetrically in quiet solution. under continuous flow-stopped flow mode. Under continuous Row operation of the cell, after a pre-concentration rime of 3 min, the pre-concentration factor was calculated to be 90. with a limit of detection of 9.5 ng/ml and a sampling rate of 15 h-1. The repeatability of the analytical signals, expressed as RSD, was always lower than 2.1%. Validation of the method was carried out by analysis of certified reference materials, and the recovery was 101.96±1.38%.

"Amine Oxidase Based Amperometric Biosensors For Histamine Detection"
Electroanalysis 2000 Volume 12, Issue 5 Pages 369-375
Mihaela Niculescu, Ivo Fr&eacute;bort, Pavel Pe?, Petr Galuszka, Bo Mattiasson, Elisabeth Cs&ouml;regi

Abstract: This work reports on the development and optimization of amperometric biosensors based on the enzyme amine oxidase (AO) for the detection of histamine, a well-known biomarker for food freshness. Biosensor characteristics were evaluated in a flow injection (FI) analysis line, operated at + 200 mV (vs. Ag/AgCl/0.1 M KCl). Two different biosensor designs were considered, one based on adsorbed AO on graphite electrodes, the detection being based on a direct electron transfer (DET) mechanism, whereas the second one based on an Os-bipyridine modified redox polymer using a mediated electron transfer (MET) pathway. Both electrode designs were able to detect histamine in µM range, however, the [osmium(4,4-dimethylbipyridine)(2)Cl](+/2+) complexed with poly(1-vinylimidazole) (PVI13-dmeOs) based electrodes showed superior characteristics with regard to stability, selectivity and linear range. These electrodes were characterized by a detection limit of 2.2 µM (calculated as three times the signal-to-noise ratio), a sensitivity of 6.8 mA M-1 cm-2, a linear range of 10^-200 µM, and an operational stability of 20 % response loss during 8 h of continuous operation at a sample throughput of 30 injections h-1.

"Enzyme Inhibition Assays With An Amperometric Glucose Biosensor Based On A Thiolate Self-assembled Monolayer"
Electroanalysis 2000 Volume 12, Issue 5 Pages 343-350
Peter W. Alexander, Garry A. Rechnitz

Abstract: A new bioelectrocatalytic enzyme membrane for biosensors based on immobilization of glucose oxidase (GOx) is evaluated for use in inhibition assays. The objectives are to show that the newly developed glucose biosensor has advantages for inhibition assays, not as a specific glucose biosensor as such. The mediator used is 2-aminoethanethiol, which forms a self-assembled monolayer on the surface of a gold electrode. The membrane configuration consists of the thiol as mediator, covalently bound to the: gold electrode and at the same time entrapped with GOx in a polyvinylpyridine (PVP) membrane. Cyclic voltammetric scans indicate a catalytic peak at + 950 mV (vs. Ag/ AgCl) after addition of glucose to a blank phosphate buffer at pH 7.4. The PVP membranes are shown to be reusable for determination of glucose for at least one week. As an example of inhibition of the enzyme reaction, the response to glucose is shown to be sensitive to the addition of Hg(II) in the ppb range with a detection limit of 0.2 ppb. Interference to CV scans from oxidizable organic compounds and other metal ions is found to be minimal, however hydrogen peroxide is the exception and interferes at 1 mM concentration.
Glucose

"Application Of Electrochemical Biosensors For Detection Of Food Pathogenic Bacteria"
Electroanalysis 2000 Volume 12, Issue 5 Pages 317-325
Dmitri Ivnitski, Ihab Abdel-Hamid, Plamen Atanasov, Ebtisam Wilkins, Stephen Stricker

Abstract: Current practices for preventing microbial diseases rely upon careful control of various kinds of pathogenic bacteria in food safety and environmental monitoring. The main disadvantages of conventional bacterial detection methods are the multistep procedure and long time requirements. This article gives an overview of alternative electrochemical biosensors for detection of pathogenic bacteria in the food industry. Focus has been on new microbial metabolism-based antibody-based and DNA-based biosensors. The underlying principles and applications of these biosensors are discussed. Recent developments in flow injection biosensor systems with an electrochemical detection are also presented.

"Selective Determination Of Vitamin B-2 At Electrochemically Activated Glassy Carbon Electrode"
Electroanalysis 2000 Volume 12, Issue 2 Pages 134-139
Kwok-Keung Shiu, Kang Shi

Abstract: Electrochemically activated glassy carbon electrodes were applied to the pre-concentration and electroanalysis of Vitamin B-2 (VB2) in multivitamin preparation. Voltammetric peak currents resulting from VB2 species adsorbed on activated electrodes showed linear response for VB2 concentrations in the range between 0.1 and 3.0 µM with a large slope of 12.2 A M-1 and a correlation coefficient of 0.996. The reproducibility of the voltammetric measurements was usually less than 7% RSD for five replicate measurements. Common vitamin and metal species did not interfere in the determination.
Preconcentration

"Microcylinder Polymer Modified Electrodes As Amperometric Detectors For Liquid Chromatographic Analysis Of Catecholamines"
Electroanalysis 1999 Volume 11, Issue 18 Pages 1333-1339
M. Marazuela, L. Ag&uuml;&iacute;, A. Gonz&aacute;lez-Cort&eacute;s, P. Y&aacute;&ntilde;ez-Sede&ntilde;o, J.M. Pingarr&oacute;n

Abstract: The use of cylindrical carbon fiber microelectrodes (CFMEs) of various mm in length modified with poly(3-methylthiophene) (P3MT) films as amperometric microsensors for the LC-EC detection of catecholamines is reported. Cyclic voltammetry at the modified microelectrodes of dopamine, epinephrine, catechol, serotonin and ascorbic acid showed electrocatalytic ability of the modified surface. This allowed the application of low potentials (+0.35 V) for the amperometric detection of the above-mentioned compounds. Flow injection measurements carried out using a 2:98 v/v methanol:0.025 mor L-1 H2PO4-/HPO42-solution Of PH 7.0, showed no evidence of fouling of the modified microelectrode surface. No cleaning or regeneration treatment was needed when working with the same polymer modified microelectrode during the whole working day. Moreover, RSD values for i(p) lower than 5 % were obtained when amperometric measurements were carried out with three different P3MT-coated CFMEs. These modified microelectrodes have also shown to be suitable for amperometric detection in HPLC. A mobile phase composed of 2:98 % methanol:phosphate buffer solution of pH 7.0 allowed a good separation of mixtures of ascorbic acid epinephrine, dopamine, serotonin and catechol with detection limits ranging between 14 and 48 pmol. Furthermore, as an application, the determination of those compounds in spiked serum samples, was accomplished with good results.

"The Use Of Chronoamperometry And Chemometrics For Optimization Of Conducting Polymer Sensor Arrays"
Electroanalysis 1999 Volume 11, Issue 18 Pages 1327-1332
Tuan A. Nguyen, Serge Kokot, Daniela M. Ongarato, Gordon G. Wallace

Abstract: A general approach using principal component analysis was applied to amperometric data obtained from flow injection analysis (FLA) to select conducting electroactive polymers (CEPs) and applied potential waveforms for discrimination of potassium and methylamine. The results were compared with the selection from the application of the PCA approach for cyclic voltammetry data in our previous research. Good agreement between the two methods of selection was found which indicates that within the general qualitative limits of the approach, PCA can be applied for selection of chemical and electrochemical parameters for FLA detection/discrimination using CEP sensor arrays detector for a range of analytes.
Principal component analysis

"Electrocatalysis And Flow Injection Analysis Of Hydrogen And Organic Peroxides At CuPtCl6 Chemically Modified Electrodes"
Electroanalysis 1999 Volume 11, Issue 16 Pages 1211-1217
Jianhong Pei, Xiao-yuan Li

Abstract: Cyclic voltammetry was used to investigate the electrochemical behavior of peroxides, both hydrogen and organic, on the CuPtCl6/GC modified electrode which displayed great electrocatalytic activity in the redox of peroxide. The results show that the electrochemical processes of peroxide on the CuPtCl6/GC modified electrode are controlled by the diffusion of the species, and the reduction of dissolved oxygen overlaps with the reduction of H2O2, but has no influence on the oxidation of H2O2 The modified electrode was characterized as an electrochemical sensor for the detection of peroxide, both hydrogen and organic, ina flow injection system. The electrode exhibited a number of great advantages such as a very wide dynamic range, quite low detection limits, high stability and short response times and simple preparation. The linear relationship between the flow injection peak currents and the concentrations of H2O2 is in a range of 5 x 10^-8 to 5 x 10^-3 M With a detection limit of 1 x 10^-8 M. The linear response to tert-butyl hydroperoxide (TBHP) is in a range of 1 x 10(5) to 2 x 10^-3 M with a detection limit of 5 x 10^-6 M.

"A Batch Injection Analysis System For Ascorbic Acid Determination Using Amperometric Detection On A Sessile Mercury Drop Electrode"
Electroanalysis 1999 Volume 11, Issue 15 Pages 1124-1129
Adriana De Donato, Jairo J. Pedrotti, Ivano G.R. Gutz

Abstract: A batch injection analysis (BIA) system, which uses an automatic mercury electrode (AME) as an amperometric detector, is described. The capillary of this AME was adapted in an inverted position through the bottom of a simple cylindrical electrochemical cell, in order to generate more stable sessile drops and to grant free access for the tip of the programmable micropipettor. The BIA system was evaluated by using the electrochemical oxidation of L-ascorbic acid to dehydroascorbic acid on the sessile mercury drop electrode. Acetate buffer solution (50 mM, pH 4.8) was used as supporting electrolyte. The working electrode was operated at +0.230 V (vs. Ag/AgCl). The effect of the dispensing rate, of the dispensed volume, of the distance between the mercury drop and the pipettor tip, as well as of the solution level in the cell were evaluated. Injections of 50 µL were suitable to reach a detection limit of about 2.5 µM (450 ppb). At the 50 µM ascorbic acid level, an RSD of 1.6% (N = 35) was observed with or without mercury drop renewal between injections. A frequency of 300 injections per hour may be reached when the drop is renewed sporadically. The new BIA method was applied to the determination of ascorbic acid in packed/canned tropical fruit juices. Selectivity was granted by differential measurements of the peak current before and after exposure of samples to ascorbate oxidase (from cucumber).
Ascorbic acid Batch injection analysis

"Potentiometric Anion Selective Sensors"
Electroanalysis 1999 Volume 11, Issue 14 Pages 1035-1048
Martijn M.G. Antonisse, David N. Reinhoudt

Abstract: In comparison with selective receptors (and sensors) for cationic species, work on the selective complexation and detection of anions is of more recent date. There are three important components for a sensor, a transducer element, a membrane material that separates the transducer element and the aqueous solution, and the receptor molecule that introduces the selectivity. This review dears with potentiometric transduction elements that convert membrane potentials into a signal. The structure and properties of membrane materials is discussed. The nature of the anion receptor ultimately determines the selectivity. Both coordination chemistry and hydrogen bonding have been used to design anion receptor molecules. The integration of all three elements by covalent linkage of all elements in durable sensorsystem concludes the review.

"Remote Monitoring And Control Of Electrochemical Experiments Via The Internet Using Intelligent Agent Software"
Electroanalysis 1999 Volume 11, Issue 14 Pages 1027-1032
Olaf Frederik, Jared Ramesh Danaraj, Bernard Fleet, Hari Gunasingham, Stephan Jaenicke, Vanessa E. Hodgkinson

Abstract: Remote monitoring and control of a flow injection anodic stripping voltammetry (FIASV) system using the Internet was attempted using various experimental methodologies. Various connections through different networks were experimented on. This was done to illustrate the concept of collaboratories as well as the feasibility of real-time control and data acquisition over a complex medium such as the Internet. The results obtained display the success of all connections and confirm the potential for such a new and promising concept.
Internet

"Electroanalytical Techniques For The Future: The Challenges Of Miniaturization And Of Real-Time Measurements"
Electroanalysis 1999 Volume 11, Issue 14 Pages 1013-1016
Christopher M. A. Brett

Abstract: A brief survey of electrochemical methods which can be employed to respond to the challenge of measuring electroactive species in untreated solutions in real-time is made. Particular attention is given to the advantages that can be obtained from miniaturization and protection of the electrode surface against fouling with polymers, together with employment of novel instrumentation techniques. The merits of the batch injection analysis approach in addressing these questions are discussed and illustrated.

"Determination Of Iodate In Salt Samples With Amperometric Detection At A Molybdenum Oxide Modified Electrode"
Electroanalysis 1999 Volume 11, Issue 9 Pages 623-626
Luis Kosminsky, Mauro Bertotti

Abstract: A method for the amperometric determination of iodate in a flow injection configuration is described. The electroreduction of the analyte occurs at a glassy carbon disk electrode modified by a molybdenum oxide layer electrochemically deposited, the film acting as an efficient electrocatalyst for the mass transport controlled reduction of iodate. The sensor is applied to the determination of iodate in a wall-jet cell coupled to a flow injection apparatus after convenient deoxygenation of the carrier solution. The linear response of the sensor is extended from 10 x 10^-6 mol L-1 to 10 x 10^-3 mol L-1 iodate with a limit of detection (signal-to-noise = 2) of 6 x 10^-6 mol L-1. The repeatability of the method for injections of a 50 x 10^-6 mol L-1 iodate solution was 6 % (n = 22). Interference from other oxidant anions (nitrate, nitrite and perchlorate) was not noticeable, whereas bromate interferes at concentrations up to 10 times that of iodate. The method was used in the determination of the iodate content in commercial salt samples.
Extraction

"Poly(catechol) Film Modified Glassy Carbon Electrode For Ultratrace Determination Of Cerium(III) By Differential Pulse Anodic Stripping Voltammetry"
Electroanalysis 1999 Volume 11, Issue 8 Pages 546-552
Soo Beng Khoo, Jing Zhu

Abstract: Oxidative electropolymerization of resorcinol, catechol and pyrogallol at the glassy carbon electrode in different media such as 0.10 M NaOH, 0.10 M phosphate buffer (pH 7.00) or 0.10 M NaClO4 all gave water-insoluble films, adherent on the electrode surface. Amongst them electropolymerization of catechol at the GC electrode in 0.10 M NaOH provided a highly sensitive and selective film for Ce(III) and therefore, this poly(catechol) film modified glassy carbon electrode was exploited for the selective pre-concentration of Ce(III) at open circuit, followed by its determination by differential pulse anodic stripping voltammetry both in batch and flow systems. Factors affecting the accumulation, stripping and removal steps were investigated and an optimized procedure was then developed. Under optimized conditions, for batch determination, the calibration plot was linear in the concentration ranges 2.00 x 10^-9 M-1.00 x 10^-8 M and 2.00 x 10^-8 M-1.00 x 10^-7 M Ce(III). A detection limit of 2.0 x 10^-10 M (0.027 ppb) (SN = 3) was found for a 10 min accumulation. For six successive determinations of Ce(III) at concentrations of 2.00 x 10^-7, 2.00 x 10^-8 and 2.00 x 10^-9 M, relative standard deviations were 3.36%, 1.76% and 4.08%, respectively. Similar results were obtained for continuous flow analysis. Interference from selected foreign ions and substances were examined. The developed method was applied to Ce(III) determination in human urine, both in batch and continuous flow systems.

"Anodic Response Of Cystine At Preanodized Au And Au-Ag Electrodes In Perchloric Acid Media"
Electroanalysis 1999 Volume 11, Issue 8 Pages 534-540
Matthew E. Johll, Dennis C. Johnson

Abstract: This study involves a comparison of the anodic response of the disulfide moiety of cystine at preanodized Au and Au-Ag rotated disk electrodes (RDEs). The goal of the study was the determination of beneficial effects that might result from the introduction of Ag-sites into Au surfaces. An anodic wave is observed for cystine at oxide covered Au and Au-Ag electrodes appearing as a shoulder to the wave for anodic discharge of water with evolution of O-2. Both the half-wave potential for the cystine wave (E-1/2,E-RSSR) and the overpotential for anodic evolution of O-2 (eta(O2) up arrow) are shifted by -3.6 mV per atomic percent Ag. These negative shifts are attributed to the higher rate of the anodic discharge of water at Ag sites in comparison to Au sites. Values for the apparent number of electrons (n(app)) transferred during oxidation of 1.0 mM cystine at 1.50 and 1.55 V (vs. SCE) are approximately 5 eq mol-1 for Au and 6 eq mol-1 for Au-80-Ag-20, as calculated from the slopes of Koutecky-Levich plots. The larger value of n(app) at the Au-Ag electrode is attributed to the higher rate for water discharge at the Ag sites. Cysteine sulfonic acid is identified as the product of extensive electrolysis (n = 10 eq mol-1) at a Au electrode. A preanodized Au electrode in a flow-through cell is demonstrated for cystine detection using a flow injection system. A 6% loss in peak response observed over a 30-min period is attributed to the slow conversion of an active surface oxide, perhaps corresponding to the equivalent of a monolayer, to an inert oxide, probably corresponding to oxide coverage exceeding a monolayer.

"Electrochemical Biosensors For Salicylate And Its Derivatives"
Electroanalysis 1999 Volume 11, Issue 8 Pages 527-533
Graciliano de Oliveira Neto, La&eacute;rcio Rover J&uacute;nior, Lauro Tatsuo Kubota

Abstract: Several methods have been employed for the quantification of salicylate and related compounds in many kinds of matrices. Special interest has been devoted over the last few years to the development of biosensors involving electrochemical techniques, due to the great selectivity and sensitivity offered by these probes. The main electroanalytical methods developed for salicylate determination in samples of clinical, biological and pharmaceutical interest are described here. A review of the most relevant advances in analytical applications of biosensors using electrochemical transducers is also described. Particular attention is dedicated to the essential advantages supplied by amperometric sensors obtained by incorporation of the bioactive elements into supporting materials, like conducting polymers, for the construction of salicylate biosensors. Some correlation between analytical parameters, such as stability and linear response range for these probes, are discussed.

"HPLC Analysis Of Carbohydrates With Electrochemical Detection At A Poly-1-naphthylamine/copper Modified Electrode"
Electroanalysis 1999 Volume 11, Issue 7 Pages 481-486
Fabiana D'Eramo, Juan M. Marioli, Alejandro A. Ar&eacute;valo, Le&oacute;nides E. Sereno

Abstract: Carbohydrates are detected by constant potential amperometric detection at a modified electrode consisting of poly-1-naphthylamine coated glassy carbon with copper ions incorporated into the polymeric matrix. The polymer is electrodeposited onto the grassy carbon surface by cyclic voltammetric experiments, and copper ions incorporated by immersion of the modified electrode in a 0.10 M cupric ions solution. The amount of copper incorporated into the polymeric matrix is regulated by controlling the immersion time. Cyclic voltammetric experiments showed that glucose was oxidized at the modified electrode surface. The catalytic current for glucose oxidation was dependent on the amount of copper incorporated. Flow injection experiments allowed the determination of the working electrode potential at which maximum signal-to-noise ratios were obtained. The electrode was successfully used in the high performance liquid chromatographic analysis of various carbohydrates.

"Amperometric Detection Of Nonelectroactive Cations In Electrolyte-free Flow Systems At Zeolite Modified Electrodes"
Electroanalysis 1999 Volume 11, Issue 6 Pages 393-400
A. Walcarius, P. Mariaulle, C. Louis, L. Lamberts

Abstract: An electrochemical detector was designed and constructed, based upon a thin-layer cell with a working electrode prepared from carbon paste modified with copper-(or silver-) exchanged zeolite particles. This electrode was then evaluated as a sensor for nonelectroactive cations in an electrolyte-free flow injection system and as an amperometric detector for suppressed ion chromatography. In the absence of supporting electrolyte, a higher signal-to-background ratio enhanced by about two order of magnitude the response obtained in electrolytic medium. Peak currents resulted from an important faradic component which was due to the electrochemical activity of the mediator-containing zeolites, while the capacitive counterpart was much lower. When applied to the analysis of alkali, alkaline earth metal and ammonium ions, in combination with a suppressed ion chromatography system, the zeolite-modified detector gave rise to reproducible amperometric responses. This resulted in chromatograms comparable to those obtained simultaneously by using a conductivity detector in series, and any extra-column effects were never observed. The most sensitive responses were achieved when using zeolites displaying the largest pore size, the highest ion exchange capacity, and the most mobile mediator, to ensure the highest exchange rates for the analytes within the zeolite framework.

"Amperometric L-lactate Biosensors: 1. Lactic Acid Sensing Electrode Containing Lactate Oxidase In A Composite Poly-L-lysine Matrix"
Electroanalysis 1999 Volume 11, Issue 5 Pages 367-373
Emmanuel I. Iwuoha, Armin Rock, Malcolm R. Smyth

Abstract: A lactic acid biosensor was prepared with lactate oxidase (LOD) from Pediococcus species, which was immobilized in a polyion membrane containing poly-L-lysine acid poly(4-styrenesulfonate). Bifunctional poly(ethyleneglycol)(400)diglycidyl ether cross-linked the polyion to a glassy carbon (GC) electrode surface modified with cobalt phthalocyanine layer. Hydrogen peroxide produced by the reaction of lactate and LOD was detected on the cobalt phthalocyanine-modified GC electrode operated at a potential of +600 mV (vs. Ag/AgCl). The response lime of the sensor to 10 µmol L-1 lactate was 1 s, and it required 45 s to give a 100% steady-state response of ~10 nA. The detection limit estimated from signal to noise ratio was 0.5 µmol L-1. The LOD/polyion biosensor exhibited electrochemical Michaelis-Menten kinetics and gave an average apparent Michaelis-Menten constant, K-M, value of 0.88±(0.07 mmol L-1 over a storage period of 18 days. Using lower molecular weight poly-L-lysine, resulted in 10 times decrease in ascorbic acid interference in lactate sensing. The polyion matrix can be constructed to be an ultrafiltration membrane to exclude electroactive compounds that interfere with lactic acid determinations in analytical samples.

"Ultrasmall Enzyme Electrodes With Response Time Less Than 100 Milliseconds"
Electroanalysis 1999 Volume 11, Issue 5 Pages 308-312
Joanna B. Meyerhoff, Michael A. Ewing, Andrew G. Ewing

Abstract: Glucose sensors with submicrometer tip diameter have been constructed by use of platinum-deposited flame etched carbon fiber electrodes. These electrodes have been coated with glucose oxidase and result in response times as Low as 85 ms. Moreover. there is a linear relationship between sensor tip diameter and response time. Although the response is, at present, only stable over a limited number of flow injection analysis runs, it appears that sensors with tip diameter less than 100 nm might provide response times of a few milliseconds if enzyme kinetics do not become rate limiting.

"Studies On The Reaction Between Nitrite And Iodide By Using Microelectrodes In Stationary And Convective Systems"
Electroanalysis 1999 Volume 11, Issue 4 Pages 234-237
V&acirc;nia Mori, Mauro Bertotti

Abstract: The chemical reaction involving iodide and nitrite at the surface of platinum disk microelectrodes has been investigated in sulfuric acid medium. Experimental conditions were adjusted to achieve a quasi-first order homogeneous catalytic reaction in quiescent solutions and the kinetic rate constant for this system was found to be 3.2 x 10(2) M-1 s-1. Preliminary experiments where electrodes of different radii were used in a wall-jet cell configuration under conditions of variable mass-transfer are presented. The results indicate the advantages of using microelectrodes in this controllable convective system for determining kinetic rate constants of homogeneous chemical reactions coupled to electrode processes.

"Graphite-ethylene/propylene/diene Terpolymer Composite Electrodes. A New Electrode Material For Electrochemical Detection"
Electroanalysis 1999 Volume 11, Issue 3 Pages 161-166
Luis Alonso, Concepci&oacute;n Parrado, Mar&iacute;a Pedrero, Lourdes Ag&uuml;&iacute;, Jos&eacute; M Pingarr&oacute;n

Abstract: The preparation and electroanalytical performance of a new composite electrode material, fabricated by mixing graphite and the ethylene/propylene/diene (EPD) terpolymer is reported. The voltammetric and flow injection with amperometric detection responses at this composite electrode of several substances of different solubilities in water are discussed and compared with those obtained at graphite-Teflon composite and glassy carbon electrodes. An EPD content around 2% ensures good compactness of the material and an adequate conductivity. Under flowing conditions, these electrodes show better signal-to-background ratios than those obtained with the other electrode materials tested. Furthermore, the new electrodes show very good resistance to fouling with no need of electrode surface pretreatment. The presence of a high content of organic solvent in the carrier solution produces a sharp decrease in the amperometric current thus limiting the advantageous use of the graphite-EPD composite electrodes to predominantly aqueous media.
Graphite

"Reticulated Vitreous Carbon-based Composite Enzyme Electrodes As Suitable Biosensors In Both Aqueous And Predominantly Nonaqueous Media"
Electroanalysis 1999 Volume 11, Issue 2 Pages 85-92
N Pe&ntilde;a, M Romero, F. J. Manuel de Villena, A. J. Reviejo, Jose M. Pingarr&oacute;n

Abstract: The construction and performance of reticulated vitreous carbon (RVC)-based composite enzyme electrodes in different aqueous and predominantly nonaqueous working media is reported. Both the mediator (ferrocene or ferrocyanide) and the enzyme peroxidase were immobilized by direct adsorption on chemically pretreated RVC cylinders. Pores of RVC were filled up with epoxy resin. The working media considered were: an aqueous phosphate solution of pH 7.4, a predominantly nonaqueous medium constituted by acetonitrile:Tris buffer (pH 7.4) mixtures, and organized media such as micellar solutions and oil-in-water emulsions. Hydrogen peroxide and 2-butanone peroxide were used as the substrates. The composite biosensors showed a good stability in ail these media. Polishing of the electrode surface everyday before working was necessary, the useful lifetime of each single electrode being of approximately 20 days. Furthermore, reproducible responses were obtained with different electrodes constructed in the same manner. Kinetic parameters V-m, K-m,K-app and k(cat) were calculated in all cases, as well as the analytical characteristics from the corresponding calibration plots. The detection limits obtained with the RVC-epoxy resin composite enzyme electrodes are, in general, considerably better than those found in the literature for bioelectrodes constructed with epoxy resin as the binder. Finally, this composite electrode also performed well in the flow injection mode.

"Electrocatalytic Oxidation Of NADH In Flow Analysis By Graphite Electrode Modified With 2,6-dichlorophenolindophenol Salts"
Electroanalysis 1998 Volume 10, Issue 18 Pages 1261-1268
Ageliki B. Florou, Mamas I. Prodromidis, Miltiades I. Karayannis, Stella M. Tzouwara-Karayanni

Abstract: The preparation of a 2,6-dichlorophenolindophenol (DCPI) modified graphite electrode is described. DCPI was immobilized by physical adsorption onto a plain graphite electrode (DCPI-CME) and onto graphite electrodes pretreated with La(NO3)3 (DCPI-La-CME) or Th(NO3)4 (DCPI-Th-CME). The electrochemical behavior of DCPI-CME was extensively studied using cyclic voltammetry. The electrochemical redox reaction of DCPI was reversible at low coverage with E0 = 55 mV (vs. Ag/AgCl/3 M KCl) at pH 6.5. A pKa value of 5.8±0.1 for immobilized form of DCPI was determined from the intersection of the lines in the plot E0 vs. pH. The current Ip has a linear relationship with the scan rate ≤1200 mV s-1, which is indicative for very fast electron transfer kinetics. The calculated value of the standard rate constant is k0 = 18±4 s-1. No decrease of either the anodic or the cathodic current of the cyclic voltammogram was observed after 500 runs of successive sweeps. The influence of the morphology of the electrode surface on the electrochemical behavior of the DCPI-CME was studied and a mathematical model was proposed, which describes the dependence of the geometrical area of the electrode surface on the grit of the emery paper. The modified electrodes were mounted in a flow injection manifold, poised at +60 mV (vs. Ag/AgCl/3 M KCl) and a catalytic current due to the oxidation of NADH was observed reducing thus the oxidation overpotential of NADH for ≈400 mV. Interference from various reductive species present in real samples was investigated. RSD was 1.2% (n = 10 for 0.1 mM NADH). The possible biosensor showed good operational and storage stability.
Nicotinamide adenine dinucleotide oxidized Electrode Electrode Voltammetry Apparatus Detector Interferences

"Horseradish Peroxidase Immobilized Electrode For Phenothiazine Analysis"
Electroanalysis 1998 Volume 10, Issue 18 Pages 1241-1248
Christine Petit, Kazuo Murakami, Arzum Erdem, Emrah Kilinc, Gemma Ortiz Borondo, Jean-Fran&ccedil;ois Liegeois, Jean-Michel Kauffmann

Abstract: A horseradish peroxidase (HRP) immobilized carbon composite electrode has been developed for the amperometric study of phenothiazine analogs. Flow injection analysis and batch experiments have been realized in acetate buffer in the presence of hydrogen peroxide. Cyclic voltammetry and amperometry using a thin-layer flow cell (dual configuration, serial mode) have permitted one to suggest the mechanisms governing the biosensor signal at -0.1 V (vs. Ag/Ag+), in the presence of hydrogen peroxide, by addition of a phenothiazine derivative It was inferred that electron transfer mediation by the phenothiazine occurred at HRP/graphite adsorbed sites, in addition to peroxidn. by dispersed HRP with substrate recycling at the graphite array-like structure of the biosensor. Thanks to these processes, high sensitivities were achieved especially in batch configurations, with amperometric detection capabilities down to 10^-8 M in acetate buffer pH 4.7. Application of the biosensor to the determination of phenothiazines in drug formulations were realized.
Drugs Phenothiazine Pharmaceutical Electrode Electrode Amperometry Sensor Apparatus Detector

"Electrocatalysis With A Dirhodium-substituted Polyoxometalate Anchored In A Xerogel-based Composite. Application To The Oxidation Of Methionine And Cystine At Physiological PH"
Electroanalysis 1998 Volume 10, Issue 18 Pages 1237-1240
Mark E. Tess, James A. Cox

Abstract: Replacing a tungsten oxide group of phosphotungstic acid with a Rh(II) acetate dimer yielded a species, Rh2POM, that catalyzed the electrochemical oxidation of L-methionine (L-Met), L-cystine, and As(III). The electrocatalytic activity of Rh2POM was greater than that of the simple Rh(II) acetate dimer in homogeneous solution A conducting carbon-composite electrode (CCE) comprising Rh2POM and carbon powder in a SiO2 matrix prepared by sol-gel chemical was catalytically active over the pH range 2-10. The CCEs produced voltammetric responses toward L-Met and L-cystine that were pH independent over the above range and were stable for at least 4 mo under dry storage. If passivated, the catalytic activity was generated by polishing. For example, a RSD of 2.9% (5 points) was obtained when the surface was polished between cyclic voltammetric experiments on 5.0 mM L-Met at pH 7.4. A least squares fit of flow injection amperometric data obtained over the range 5-156 µM L-Met (7 points) yielded the following: slope 0.85 µA mM 1; intercept 0.05 µA; and r = 0.995. The detection limit was 2.3 µM.
l-Methionine Amperometry Electrode Sensor pH Apparatus Detector Catalysis

"Mytilus Edulis Adhesive Protein (MAP) As An Enzyme Immobilization Matrix In The Fabrication Of Enzyme-based Electrodes"
Electroanalysis 1998 Volume 10, Issue 17 Pages 1193-1199
Coralie Saby, John H.T. Luong

Abstract: A simple enzyme immobilization technique using an adhesive protein isolated from Mytilus edulis blue mussels was optimized for constructing a glucose oxidase (GOD) based electrode. Owing to the presence of 10^-15% of 3,4-dihydroxyphenylalanine residues, the mussel adhesive protein (MAP) was easily oxidized to form a stable protein film on Pt, Au, and glassy C electrodes. Covalent attachment of glucose oxidase to adhesive protein modified electrodes was attained since the oxidized form of the L-Dopa moieties was very reactive towards various compounds containing amino, alcohol, and thiol groups. Glucose detection was performed using MAP/GOD modified electrodes at +0.8 V in 0.1 M phosphate buffer, pH 5. Pt modified electrodes (Pt/MAP/GOD) exhibited a considerably higher sensitivity (1.28 µA/mM) in comparison to its Au (Au/ MAP/GOD, 2.92 nA/mM) or glassy carbon (GC/MAP/GOD, 2.62 nA/mM) counterparts. Tetrachloro-1,4-benzoquinone (TCBQ), an oxidation product of pentachlorophenol, was detected using MAP/GOD modified electrodes at +0.45 V, in a deaerated 0.1 M tartaric acid buffer, pH 3.5 containing 40 mM glucose. In steady state, the current response of the Au/MAP/GOD electrode was higher (6.62 nA nM-1 cm-2, t95≈83 s, 5 nM) than the GC/MAP/GOD electrode (3.78 nA nM-1 cm-2, 8 nM). In flow injection analysis, GC/MAP/GOD electrodes exhibited a linear response for TCBQ ranging from 10 nM to 1 µM (3.96 nA nM-1) with a detection limit of 10 nM. The modified glassy C enzyme based electrode retained 90% and 87% of its activity after 150 and 250 repeated injections.
tetrachloro-1,4-benzoquinone Electrode Electrode Electrode Electrode Immobilized enzyme Apparatus Detector

"Electrocatalysis And Amperometric Detection At A Ruthenium-modified Indium-hexacyanoferrate Film Electrode"
Electroanalysis 1998 Volume 10, Issue 17 Pages 1163-1167
Tommaso R.I. Cataldi, Giuseppe E. De Benedetto, Alfonso Bianchini

Abstract: The electrocatalytic activity of a glassy carbon electrode modified with electrochemically deposited indium(III)-hexacyanoferrate (InHCF) film, which was subsequently cycled in a solution of Ru(III), is described. Although the resulting Ru-modified InHCF thin film electrode behaves in a manner analogous to the parent InHCF film, its stability was improved. Such a modified electrode was characterized, in acidic (pH 2) 0.5 M KCl solutions, by cyclic voltammetry, and FIA. It exhibits a high catalytic activity for the electrooxidation of some inorganic and organic compounds of anal. interest, such as As(III), S2O32-, cysteine, and 2-furaldehyde. The anal. applicability of this novel ruthenium-modified InHCF film electrode for the amperometric detection in flowing streams is discussed. Repetitive sample injections with amperometric detection of S2O32- at +0.8 V (vs. Ag/AgCl) as applied potential produced a stable response over 8 h of operation, making it very attractive for practical applications.
Arsenic(3+) Sulfite Cysteine 2-Furaldehyde Amperometry Electrode Apparatus Detector

"Protein Detection Using Conducting Polymer Microarrays"
Electroanalysis 1998 Volume 10, Issue 16 Pages 1101-1107
W. Lu, T. A. Nguyen, Gordon G. Wallace *

Abstract: An array of conducting polymer coated microelectrodes was employed as an amperometric detector to analyze a range of proteins in a FIA system. Using conducting polymer coatings with different counterions (dyes) incorporated, varying selectivity series were obtained. Protein identification and quantification were performed using chemometric techniques such as principal component anal., soft independent modeling of class analogy, ordinary least square, and partial least square. Using 4 different polypyrrole-based polymers, response patterns were obtained and classification of 6 proteins was achieved. Individual proteins in a 2 component mixture were quant. analyzed with acceptable accuracy.
Protein Electrode Amperometry Electrode Chemometrics Principal component analysis Multidetection

"Solid-state Ion-selective Electrode Arrays"
Electroanalysis 1998 Volume 10, Issue 16 Pages 1096-1100
Aoga'n Lynch, Dermot Diamond *, Patrick Lemoine, Jim McLaughlin, Matt Leader

Abstract: Variable pressure scanning electron microscopy is demonstrated to be a powerful method for directly studying swelling processes occurring during conditioning of PVC-membrane ion-selective electrodes containing a salt-doped hydrogel layer between the PVC and the internal Ag/AgCl reference electrode. Using an in-house developed virtual instrument interface and a portable PC fitted with a PCMCIA data acquisition card, it is relatively easy to adapt arrays manufactured for blood-gas analysis for other applications which involve the determination of mixtures of inorganic ions. The simultaneous analysis of sodium and chloride over concentration ranges associated with the diagnosis of cystic fibrosis (CF) in sweat is demonstrated as an example.
Sodium Chloride Electrode Electrode Electrode Apparatus Detector pH

"Renewable-Reagent Enzyme Inhibition Sensor For Remote Monitoring Of Cyanide"
Electroanalysis 1998 Volume 10, Issue 15 Pages 1034-1037
Joseph Wang*, Baomin Tian, Jianmin Lu, Doug MacDonald, Jianyan Wang, Dengbai Luo

Abstract: A renewable-reagent flow probe has been developed for the remote electrochemical biosensing of enzyme inhibitors. The new submersible device addresses the challenges of continuously replacing the inhibited enzyme and consumed substrate. The internal delivery of microliter enzyme and substrate solutions is coupled to an in situ microdialysis sampling of the toxin, and an amperometric detection of the enzymatically generated product. The new concept is demonstrated for the detection of micromolar concentrations of free cyanide in the presence of the enzyme tyrosinase and its catechol substrate. The optimization of various physical and chemical parameters has resulted in a low detection limit of 2 x 10^-6 M cyanide and good precision (RSD = 5%). The new device holds great promise for in situ environmental and industrial monitoring of toxins.

"Electrooxidation Of Aliphatic Amines And Their Amperometric Detection In Flow Injection And Liquid Chromatography At A Nickel-based Glassy Carbon Electrode"
Electroanalysis 1998 Volume 10, Issue 15 Pages 1005-1009
Innocenzo G. Casella *, Simona Rosa, Elio Desimoni

Abstract: The electrocatalytic oxidation of mono- and poly-amines was investigated in alkaline solutions at a nickel-based chemically modified glassy carbon electrode. -NiOOH exhibited electrocatalytic activity towards amines oxidation. FIA experiments were performed to test the electrode as an amperometric sensor. Under constant-potential amperometric mode (at 0.55 V vs. 4,0 M Ag/AgCl/Cl-), detection limits of all investigated analytes ranged within 1.2-3.8 pmol (S/N = 3), and the linear dynamic range extended over three orders of magnitude above the detection limits. Chromatographic separations, performed by an ion moderated partition column in alkaline solutions equipped with the Ni-CME detector, allowed very simple quantitation of aliphatic amines, avoiding tedious and time-consuming derivatization processes or post-column addition procedures. The Ni-CME showed good temporal stability and appreciable sensitivity.
Amines, aliphatic Serum Human Amperometry Electrode HPIC Catalysis

"A Novel Assembly For Perfluorinated Ion-exchange Membrane-based Sensors Designed For Electroanalytical Measurements In Nonconducting Media"
Electroanalysis 1998 Volume 10, Issue 14 Pages 942-947
Rosanna Toniolo, Nicola Comisso, Gino Bontempelli *, Gilberto Schiavon, Stefano Sitran

Abstract: A perfluorinated ion-exchange membrane-based sensor suitable for electroanal. measurements in electrolyte-free media is described, which was assembled following a novel design enabling an easier preparation procedure. It was fabricated by inserting the terminal portion of a working Pt wire electrode into a Nafion tubing of suitable diameter and welding the wire thus wrapped to the bottom of a cell body by an insulating epoxy resin. The remainder upper part of the working electrode was covered by a Teflon tubing to avoid the elec. contact with the internal electrolyte introduced into the cell body, which was equipped with a counter and a reference electrode. As a result of this configuration, the actual working-electrode surface is the wire circumference contacted by the polyelectrolyte material at the bottom of the assembly which is exposed to the sample. The performance of this sensor was tested by cyclic voltammetry, amperometric monitoring and flow injection analysis for the electroanal. of a series of prototype analytes either dissolved in electrolyte-free water (H2O2, hydroquinone, ferricyanide, I- and Br-) or present in N2 atmospheres (triethylamine and O2). Detection limits for these analytes were estimated (s = 3), together with the corresponding ranges within which the responses display a linear dependence on the analyte concentration. The novel assembly is suitable only for the anal. in electrolyte-free liquid samples, while for the anal. of gaseous atmospheres, especially for flowing gases, ion-exchange membrane sensors prepared by the more usual procedure based on the use of working electrode materials embedded into a moist polyelectrolyte membrane should be preferred.
Hydrogen peroxide Hydroquinone Ferricyanide Iodide Bromide Triethylamine Oxygen, molecular Sensor Ion exchange Electrode Electrode Nafion membrane Apparatus Detector

"Selective Determination Of Methylmercury By Flow Injection Fast-scan Voltammetry"
Electroanalysis 1998 Volume 10, Issue 13 Pages 926-930
Rebecca Lai, Eva L. Huang, Feimeng Zhou *, David O. Wipf

Abstract: A simple flow injection system, suitable for solution flow rates at microliters-per-minute, was combined with fast-scan voltammetry for selective determination of MeHg+. A thin Hg film was formed at a Pt microelectrode prior to the measurement. Detection of MeHg+ is carried out by measuring the oxidation of MeHg radicals that were generated at the Hg microelectrode. At slow scan rates, the electrogenerated MeHg radicals undergo a follow-up dimerization reaction to form M2Hg2 (ErCi2 mechanism). At fast scan rates, MeHg radicals can be quantitatively reoxidized (reversible electron-transfer). Optimization of the experimental conditions of the system was performed based on studies of the relationship between the scan rate and the dimerization rate of the MeHg radical. Under optimized conditions, detection level of sub-nanomole was obtained with a sample consumption <10 µL, and the concentration. detection limit for MeHg+ at 50 V/s was estimated to be ~0.56 µM. To demonstrate the applicability of this method to automatic analysis, repetitive fast-scan cyclic voltammetry was conducted in conjunction with multiple sample injections. Determination of MeHg+ in the presence of excess inorganic Hg was also conducted. This approach to MeHg+ determination was successfully applied to the analysis of elevated dogfish muscle samples.
Methylmercury ion Dogfish Fish Tissue Voltammetry Electrode Electrode Speciation Optimization Apparatus

"A New Method For The Evaluation Of The Antioxidant Power Of Wines"
Electroanalysis 1998 Volume 10, Issue 13 Pages 908-912
Saverio Mannino*, Oreste Brenna, Susanna Buratti, Maria Stella Cosio

Abstract: Phenols present in wines are responsible for its antioxidant properties. Traditionally the antioxidant power of wines has been measured using in vitro tests principally based on the inhibition of human LDL oxidation and also using the ORAC assay with different reactive species. This work describes a new method to evaluate the antioxidant power of several red and white wines based on a FIA system with electrochemical detection. It represents a significant improvement over other previously reported methods since it is based on the chemical structure of polyphenols and does not require the use of reactive species.

"Amperometric Differential Determination Of Ascorbic Acid In Beverages And Vitamin C Tablets Using A Flow Cell Containing An Array Of Gold Microelectrodes Modified With Palladium"
Electroanalysis 1998 Volume 10, Issue 13 Pages 887-890
Renato C. Matos, M&aacute;rcio A. Augelli, Jairo J. Pedrotti, Claudimir L. Lago, L&uacute;cio Angnes

Abstract: A simple and attractive method for quantification of ascorbic acid (AA) in beers, soda, natural juices, and commercial vitamin C tablets was developed by combining flow injection analysis and amperometric detection. An array of Au microelectrodes electrochemically modified by deposition of Pd was employed as working electrode which was almost unaffected by fouling effects. AA was quantified in beverages and vitamin tablets using amperometric differential measurements. The method is based on three steps involving the flow injection of the sample plus a standard addition of AA, of the pure sample, and of the enzymatically-treated sample. The enzymatic treatment was carried out with Cucumis sativus tissue, which is a rich source of ascorbate oxidase, at pH 7. The calibration plots for freshly prepared AA standards were linear in the concentration. range of 0.18-1.8 mg/L with a relative standard deviation (RSD) <1%, while for real samples the deviations were 2.7-8.9%.
Ascorbic acid Beer Soft drink Fruit Pharmaceutical Amperometry Electrode Electrode Differential detection Standard additions calibration Enzyme

"Optimization Of Response Of The Silver Oxide Electrode For The Detection Of Carbohydrates And Related Compounds"
Electroanalysis 1998 Volume 10, Issue 12 Pages 836-841
James M. DeMott Jr., Terrence P. Tougas, Edwin G. E. Jahngen

Abstract: The response of the silver oxide electrode to carbohydrates, polyhydroxy compounds and amines is dependent on several factors. These include the number of oxidizable groups on the substrate and the way in which the electrode surface is prepared, including the potential program, the thickness of the oxide layer, the surface area and the presence of other species in the solution during electrode conditioning. Studies of these factors led to a pulsed potential program for the conditioning and maintenance of electrode stability, with the incorporation of phosphate during the initial conditioning process. This method led to a response to 10^-4 M glucose, which was reproducible for at least forty repeated injections and stable for at least four hours with a relative standard deviation of 5.2 %. This response was also reproducible on successive days when the electrode was prepared in the same manner.
Glucose Electrode Detector

"Determination Of Tert-butylhydroxytoluene By Flow Injection Analysis At Polymer Modified Glassy Carbon Electrodes"
Electroanalysis 1998 Volume 10, Issue 12 Pages 832-835
C.D. Garcia, P.I Ortiz*

Abstract: A flow injection method for the determination of the antioxidant BHT using polymer modified electrodes in connection with amperometric detection is proposed. The procedure is based on the electrochemical oxidation at 0.700 V (vs. Ag/AgCl [3 M NaCl]) in phosphate buffer solution (pH 7.2). BHT is determined over the range 0.001-0.020 or 0.005-0.030 g/L. Other analysis parameters, such as electrode working potential, flow rate, electrodeposited charge, and solution pH were optimized. The proposed method was applied to the determination of BHT in electrical transformer and vegetable oils samples. The results were compared with the HPLC-UV detection standard technique.
tert-Butylhydroxytoluene Oil Oil Electrode Electrode Amperometry Optimization Method comparison

"A Six Sensor Array Of Coated-wire Electrodes For Use In A Portable Flow Injection Analyzer"
Electroanalysis 1998 Volume 10, Issue 10 Pages 707-712
Peter W. Alexander*, Telis Dimitrakopoulos, D. Brynn Hibbert

Abstract: An array of 5 photo-cured epoxydiacrylate membrane electrodes incorporating ionophores and a Ag/AgCl wire electrode used as a chloride sensor were all used simultaneously in a previously reported multielectrode flow cell and in a portable flow injection analyzer described by P. Alexander et al. (1996). Photo-cured coated-wire electrodes for NH4+, Ca2+, H+ (pH), NO3-, and K+ and Ag/AgCl wire-based chloride electrode were developed for remote-site monitoring. The photo-cured membranes prepared exhibited strong adhesion to the metal substrate and showed improved mech. strength compared to PVC-based membranes. Each sensor in the present electrode-array exhibited near-Nernstian response over a log-linear range from 0.1-10 mM with detection limits of 0.01 mM in the flow injection potentiometric mode. The flow injection cell was capable of determining the respectively. ions in various water samples and the results were in good agreement with comparative anal. methods.
Chloride Ammonium Calcium pH Nitrate Potassium Water Electrode Electrode Electrode Potentiometry Method comparison

"Anodic Stripping Of Heavy Metals Using A Hanging Mercury Drop Electrode In A Flow System"
Electroanalysis 1998 Volume 10, Issue 10 Pages 701-706
Cecilia Fern&aacute;ndez-Bobes, Maria Teresa Fern&aacute;ndez-Abedul, Agust^iacute;n Costa-Garci&aacute;

Abstract: A hanging mercury drop electrode, included in a low deal volume thin layer flow cell, has been used for on-line simultaneous determination of the trace metals Cd, Pb, Cu and Zn. Parameters related either to the flow system or to the differential pulse anodic stripping technique were optimized. Internal standard and standard additions quantitation methods were tested. Bi was chosen as internal standard and adequate conditions for the stripping medium were studied. The method was applied to the determination of these metals in algae samples of the north coast of Spain. The results compared favorably with those obtained by ICP-MS.
Metals, heavy Copper Lead Cadmium Zinc Uranium Marine Voltammetry Electrode

"Determination Of Codeine In Human Plasma And Drug Formulation Using A Chemically Modified Electrode"
Electroanalysis 1998 Volume 10, Issue 8 Pages 536-540
Jyh-Myng Zen*, Ming-Ren Chang, Hsieh-Hsun Chung, Ying Shih

Abstract: Both flow injection methodology and square-wave voltammetry were developed and evaluated for determining codeine in human blood plasma and pharmaceutical formulations using a Nafion/Ru oxide pyrochlore chemical modified electrode. Combining the electrocatalytic function of the Ru oxide pyrochlore with charge-exclusion and the pre-concentration features of Nafion perform well in codeine detection. Compared to a bare glassy C electrode, the chemical modified electrode exhibits a shift of the oxidation potential in cathodic direction and a marked enhancement of the current response. A linear calibration plot is obtained over the 0-32 µM range in 0.05 M HClO4 solution with a detection limit (3s) of 10 nM in the square-wave voltammetric method. While, in flow injection anal., a linear calibration plot is obtained over the 0.5-40 µM range with a detection limit of 0.86 ng. Quant. anal. was performed by the standard addition method for codeine content in human plasma and a commercial available drug.
Codeine Plasma Human Pharmaceutical Electrode Electrode Voltammetry Method comparison Apparatus Detector

"Use Of Prussian Blue/conducting Polymer Modified Electrodes For The Detection Of Cytochrome C"
Electroanalysis 1998 Volume 10, Issue 7 Pages 472-476
W. Lu, G.G. Wallace *, A.A. Karayakin

Abstract: The development and utilization of a Prussian blue/conducting polymer composite electrode was investigated. The introduction of a layer of conducting polymer (polypyrrole) enhanced the electroactivity of the outer Prussian blue film. This was used for improved signal generation for the redox protein cytochrome c. The effect of the thickness of these 2 film coatings and buffer solution pH was investigated. The anal. utility was demonstrated using flow injection anal.
Cytochrome C Electrode Electrode Sensor Optical isomers Apparatus Detector

"Electrostatically Assembled Films For Improving The Properties Of Tetraruthenated Porphyrin-modified Electrodes"
Electroanalysis 1998 Volume 10, Issue 7 Pages 467-471
Carla M.N. Azevedo, Koiti Araki, L&uacute;cio Angnes, Henrique E. Toma

Abstract: Modified electrodes, suitable for use in flow injection anal., were obtained by the electrostatic assembly of films constituted by 2 different porphyrins, namely, µ-meso(tetrapyridyl)porphyrinatecobalt(III)tetrakis[bis(bipyridine)(chloro)ruthenium(II)] and meso-tetra(4-sulfonatephenyl)porphyrinatezinc(II), forming alternating layers onto glassy carbon surfaces. The films were studied by cyclic voltammetry and proved to be strongly adherent and highly stable. They could be used for at least a week without loss of sensitivity. In addition, they exhibit an enhanced amperometric response and good protection against fouling, e.g., by phenol oxidation products. Their usefulness in flow injection analysis of NO2- and SO32- was demonstrated. Excellent signal to noise ratios were obtained for SO32- down to 10^-6 mol/L, and for NO2- down to 10^-7 mol/L.
Sulfite Nitrite Amperometry Electrode Electrode Apparatus Detector

"Pyranose Oxidase-modified Carbon Paste Electrodes For Monosaccharide Determination"
Electroanalysis 1998 Volume 10, Issue 4 Pages 223-230
Helena Lid&eacute;n, Jindrich Volc, Gy&ouml;rgy Marko-Varga, Lo Gorton

Abstract: An amperometric biosensor for the detection of some monosaccharides was developed with co-immobilized pyranose oxidase (purified from the basidiomycete fungus Phanerochaete chrysosporium) and horseradish peroxidase in carbon paste. Due to rather low selectivity of pyranose oxidase, the biosensor could detect both predominating anomers of D-glucose as well as the substrates D-xylose, D-galactose, and -gluconolactone. The best sensor performance was obtained from a carbon paste with covalently immobilized enzymes together with the additives lactitol and polyethylenimine, resulting in a sensitivity for glucose of 30.2 A cm-2 mM 1. The enzyme modified electrode was investigated in an automated flow injection system at the operating potential of -50 mV (vs. Ag/AgCl) with an injection frequency of 40 h-1. The biosensor was also integrated as the detection unit in a liquid chromatographic system for the detection of monosaccharides to show its potential use in real applications.
Monosaccharides Electrode Electrode

"Microporous Gold Electrodes As Combined Biosensor/electrochemical Detectors In Flowing Streams"
Electroanalysis 1998 Volume 10, Issue 3 Pages 157-162
Michael W. Ducey Jr., Mark E. Meyerhoff

Abstract: Microporous gold electrodes are described for use as flow-through biosensor/electrochemical detectors in both flow injection analysis (FIA) as well as post-column detection in HPLC. Electrodes prepared by the covalent immobilization of tyrosinase onto the electrode surface (via a chemisorbed layer of thioctic acid and polylysine) are used to demonstrate the utility of the electrode. Such electrodes are shown to respond to a variety of substituted phenols under FIA conditions at applied potential of only -50 mV (vs. Ag/AgCl). Detection limits of 0.5 µM catechol and 3.4 µM phenol were achieved with a sample throughput rate of 38 samples/h. The electrode is shown to be stable for up to 14 days of use. The porous bioelectrode is shown to be useful as a post-column detector for substituted phenols following their separation by HPLC. Various techniques for immobilization of the enzyme onto the electrode surface (covalent and noncovalent) as well as factors affecting sensitivity and through-put (buffer ionic strength and addition of organic modifier) are discussed.
Electrode Sensor Electrode Apparatus Detector Optimization

"Critical Comparison Of Paraffin Carbon Paste And Graphite-poly(tetrafluorethylene) Composite Electrodes Concerning The Electroanalytical Behavior Of Various Antioxidants Of Different Hydrophobicity"
Electroanalysis 1998 Volume 10, Issue 1 Pages 33-38
Emilia Diego, Lourdes Ag&uuml;i, Araceli Gonz&aacute;lez-Cort&eacute;s, Paloma Y&aacute;nez-Sedeno, Jos&eacute; M. Pingarro&oacute;n, Jean-Michel Kauffmann

Abstract: The voltammetric and flow injection amperometric behaviors of several substances used as antioxidants in the food and pharmaceutical industries at carbon paste electrodes, with paraffin as binding agent, and at graphite-40% PTFE composite electrodes were compared on the basis of the different hydrophobicity of the antioxidants. Aqueous solutions, alcohol-water mixtures and oil-in-water-emulsions were used as working media. No voltammetric or flow injection responses were obtained for high hydrophobic antioxidants (BHT, Irganox-1076 and Irganox-1010) at graphite-PTFE electrodes. On the contrary, carbon paste electrodes allowed the attainment of analytically useful signals for these compounds. A pulse amperometric detection (PAD) scheme should be applied in these cases for the cleaning of the electrode surface. The use of graphite-PTFE electrodes seems to be advantageous for the less hydrophobic antioxidants such us propyl gallate and TBHQ. An adsorption process for PG and a faster electrode kinetic in the case of TBHQ were shown to occur by cyclic voltammetry at the PTFE composite electrode. Furthermore, this electrode allows the use of lower potentials for the amperometric detection of these compounds than the carbon paste electrode. Good reproducibility of the successive amperometric responses was also observed. The mutual influence of the electrode surface composition and the lipophilic characteristics of the molecules tested is discussed.
Irganox 1076 Irganox 1010 Cresol, 4-, 2-6-di-tert-butyl Amperometry Electrode Electrode Apparatus

"The Determination Of Silver In Photographic Emulsions By Discontinuous Flow Analysis"
Electroanalysis 1998 Volume 10, Issue 1 Pages 21-25
A. J. Dole, T. J. Cardwell, R. W. Cattral, R. Di Giacomo, C. G. Rodrigue, G. R. Scollary

Abstract: An investigation of the use of the flow-based procedure of discontinuous flow analysis (DFA) for the determination of silver in photographic emulsions is described. It is shown that a procedure used by the photographic industry which involves the complexation of a silver halide with the thiosulfate ion followed by titration with thioacetamide produces poor repeatability when applied in DFA. Evidence is presented to demonstrate that this is due to a slowing of the response of the silver sensor used to detect the end-point in the titration which is caused by the formation of a loosely bound layer of silver sulfide on the sensor surface. This surface layer has been identified using scanning electron microscopy and cyclic voltammetry. An alternative procedure is proposed for the determination using DFA which involves complexing the silver halide (bromide) with the cyanide ion followed by titration with sodium sulfide. The results from this method are within 2% compared with those obtained by AAS.

"Photo-cured Ammonium And Hydrogen-ion Selective Coated-wire Electrodes Used Simultaneously In A Portable Battery-powered Flow Injection Analyzer"
Electroanalysis 1997 Volume 9, Issue 17 Pages 1331-1336
Peter W. Alexander*, Telis Dimitrakopoulos, D. Brynn Hibbert

Abstract: Nonactin and N,N-dioctadecylmethylamine ionophores, each in an epoxydiacrylate polymer, were photo-cured on silver wires (0.8 mm i.d.) and evaluated as ammonium and hydrogen (pH) coated wire electrodes. The photo-cured membranes prepared in this study exhibited excellent adhesion to the metal substrate and improved mechanical strength compared to PVC based membranes. The ammonium electrode exhibited a Nernstian response over a concentration range between 0.01 mM and 100 mM with a detection limit of 0.0005 mM. The ammonium electrode exhibited improved selectivity against most common interfering ions, including potassium compared to previous studies. The hydrogen selective electrode exhibited a near-Nernstian slope of 55.9±0.8 mV change/log a((H+)) between pH 4.0 and pH 11.0 in the steady-state mode. The ammonium and pH sensors each responded quickly reaching 90% of steady-state value in<5s, making these coated wire sensors ideal for flow injection potentiometry measurements. In the FIP mode, both the photo-cured ammonium and pH electrodes exhibited near-Nernstian responses of 49.2±1.0 mV change/activity decade and 50.2±0.4 mV change/log a((H+)), respectively, over a similar concentration range as in the steady-state mode. The photo-cured ammonium and pH electrodes were used simultaneously in the analysis of hydroponic nutrient solutions and waste water samples obtained from a local greenhouse grower in the flow injection potentiometric mode. 29 References
Ammonium pH Water Waste Electrode Electrode Potentiometry Electrode Electrode Simultaneous analysis Portable Interferences

"Microelectrode Procedures For The Determination Of Silicate And Phosphate In Waters Fundamental-studies"
Electroanalysis 1997 Volume 9, Issue 17 Pages 1311-1317
Neil G. Carpenter, Alexia W. E. Hodgson, Derek Pletcher *

Abstract: The voltammetry of the molybdosilicate and molybdophosphate complexes, formed by the addition of hexafluorosilicate and phosphate to an acidic sodium molybdate solution, have been defined at gold microdisk electrodes. It is shown that the reaction conditions influence both the kinetics of formation of the complexes and their voltammetry. It is possible to find conditions where the steady state amperometric response of the Au microdisk electrodes allows a rapid and convenient method for the determination of silicate and phosphate at concentrations in the range 1-1000 µM. 30 References
Silicate Phosphate Water Amperometry Electrode Electrode Electrode Kinetic Optimization Complexation Steady state

"Electrocatalytic Oxidation And Flow Amperometric Detection Of Hydrazine At An Electropolymerized 4-vinylpyridine/palladium Film Electrode"
Electroanalysis 1997 Volume 9, Issue 15 Pages 1205-1208
Tao Li, Erkang Wang *

Abstract: A poly(4-vinyl)pyridine (PVP)/Pd film electrode was constructed for the electrocatalytic detection of hydrazine. The preparation of the PVP/GC electrode was performed by electropolymerization of the monomer 4-vinylpyridine onto the surface of a glassy carbon electrode. Subsequently, palladium is electrodeposited onto the polymer modified electrode surface. The ion-exchange function of PVP polymer is helpful to this process in view of the tetrachlorapalladate anion. Compared with the Pd/GC electrode, the modified electrode displays a better mechanical stability in a flowing stream. The PVP/Pd film electrode exhibits higher sensitivity when detecting hydrazine with a detection limit of 0.026 ng (S/N=3).

"Conducting Phenylenevinylene Blends As Electrode Materials In LC Amperometric Detection"
Electroanalysis 1997 Volume 9, Issue 15 Pages 1197-1200
E. Staes*, L. J. Nagels, G. Verreyt, S. Jacobs, Y. Bao, H. J. Geise

Abstract: A novel amperometric electrode based on a conducting polymer is presented and its properties are compared with those of a glassy carbon electrode. The electrode material was made by mixing 2,5-dimethoxy-1,4-bis(2-(3,4,5-trimethoxy-phenyl)ethenyl)benzene with iodine and polycarbonate. The blend was coated on a glassy carbon electrode by evaporation from a chloroform solution. Catecholamines were used as test substances in LC and FIA measurements. They were oxidized at a potential of +0.7 V (vs. SCE). The electrode exhibited a linear response for injected concentrations from 2.5 X 10^-6 M to 2.5 X 10^-3 M. It had a response time of 1.2 s and a coulometric efficiency of 0.74% at a linear flow rate of 1 mL/min. The electrode material is stable for several months under normal operating conditions. Hydrodynamic voltammograms showed E1/2 values shifted by approximately 100 mV as compared to glassy carbon. The novel redox-conducting coating is proposed as an alternative material for the development of enzyme electrodes and chemically modified electrodes.
Catecholamines Amperometry Electrode

"Carbon Packed-bed Upstream Electrode In Combination With A Downstream Thin-layer Cell For Dual Electrode Applications In Microbore Liquid-chromatography And Flow Injection Analysis"
Electroanalysis 1997 Volume 9, Issue 15 Pages 1163-1166
H. G. Jayaratna*, Liu Yang, T. Huang, C. S. Bruntlett, P. T. Kissinger

Abstract: A flow-through electrode with a high conversion efficiency has been developed for chromatographic detection as well as other online electrochemical applications. A small length of reticulated vitreous carbon material of high pore density permits excellent conversion of some organic compounds. This can easily be employed in dual electrode applications with radial or cross flow thin-layer detectors. When used as a generator electrode, it can improve selectivity for electrochemically active compounds in chromatographic detection and microdialysis/biosensor combinations. 11 References
Electrode Sensor Dual detection Dialysis

"Graphite-Teflon-peroxidase Composite Electrodes"
Electroanalysis 1997 Volume 9, Issue 14 Pages 1113-1119
Maria Antonia del Cerro, Gabriela Cayuela, A. Julio Reviejo, Jose M. Pingarr&oacute;n *, Joseph Wang

Abstract: The performance of graphite-70% Teflon-peroxidase-ferrocene composite electrodes, fabricated by simple physical inclusion of the enzyme and the mediator into the bulk of a graphite-Teflon matrix, by using both batch and flow injection modes, is reported. The electrode responds very rapidly to changes in H2O2 concentration due to the absence of a membrane barrier on the electrode surface and of a covalent attachment of the enzyme to graphite. The composite enzyme electrode showed a long-term operation due to the renewability of its surface by polishing. Reproducible amperometric responses were achieved with different electrodes fabricated from different composite matrices, and no significant loss of the enzyme activity was observed after seven months of dry-storage at 4°C. A bienzymatic graphite-70% Teflon-peroxidase-glucose oxidase-ferrocene electrode has been developed, too, showing a rapid response to the changes in the glucose concentration. The stability of the bienzymatic composite electrode was similar to that of the peroxidase biosensor. This biosensor was applied to the determination of glucose in must and wine samples by batch amperometry and flow injection with amperometric detection modes.
Glucose Wine Must Amperometry Electrode Sensor Electrode Electrode Apparatus

"Hydrocarbon Pasting Liquids For Improved Tyrosinase-based Carbon Paste Phenol Biosensors"
Electroanalysis 1997 Volume 9, Issue 14 Pages 1102-1106
Joseph Wang *, Fang Lu, Stephen A. Kane, Yong-Kook Choi, Malcolm R. Smyth, Kim Rogers 5

Abstract: Short-chain hydrocarbons are used as pasting liquids in carbon-paste tyrosinase amperometric biosensors. The response of the phenolic substrates decreases rapidly upon increasing the chain length of the hydrocarbon binder from C10 to C14, and then it levels off to a size similar to that of the mineral oil biosensor. For example, the dodecane-based enzyme electrode offers a 17.8-fold signal enhancement compared to the mineral-oil one. Such sensitivity enhancements are attributed to the extractive accumulation of the phenolic substrates. The change in the carbon-paste binder influences also the selectivity of the tyrosinase electrode and the Km, app values. Flow-injection analysis yields a detection limit of 6 nM catechol and a relative standard deviation of 2.5% (n = 30). A dual enzyme electrode chromatographic detection, based on the use of different pasting liquids, provides unique characterization of the phenolic substrates. The merits of this strategy are illustrated in connection with a river water sample.
Phenol Electrode Sensor Electrode

"Amperometric Sensing Of Ammonia In Aqueous Solutions Using A Polyaniline-modified Electrode In Flow Injection Systems"
Electroanalysis 1997 Volume 9, Issue 14 Pages 1062-1066
Marek Trojanowicz *, Tadeusz Krawczyski vel Krawczyk, Magorzata Zmorzyska, Luigi Campanella

Abstract: Platinum electrode modified with polyaniline by electropolymerization exhibits amperometric sensitivity to nonprotonated ammonia in aqueous solutions in the anodic range of potentials. Sensitivity of response depends mostly on the kind of doping anions used and the polarization potential applied during measurements. This detection can be utilized for design of amperometric biosensors for urea.
Ammonia Amperometry Electrode Sensor

"On-line Flow Sensor For Measuring Acetylcholine Combined With Microdialysis Sampling Probe"
Electroanalysis 1997 Volume 9, Issue 12 Pages 912-916
Tsutomu Horiuchi*, Keiichi Torimitsu, Katsunobu Yamamoto, Osamu Niwa

Abstract: We have developed an on-line electrochemical sensor for the continuous measurement of acetylcholine (ACh). The sensor comprises a small volume prereactor containing immobilized choline oxidase (ChOx) and catalase (or horseradish peroxidase, HRP), a small volume enzymatic reactor containing immobilized acetylcholine esterase (AChE) and ChOx and a glassy carbon electrode modified with Os-polyvinylpyrridine -HRP. The sensor can measure ACh selectively even when the choline (Ch) concentration is more than 1000 times that of ACh, when th ChOx and catalase are immobilized in the prereactor. The sensor shows a wide linear relationship from 5 nM to 1 M and a detection limit of 5 nM (S/N = 2), which is comparable to the ACh detection limit achieved by liquid chromatography/electrochemistry. It also shows high selectivity against other neurotransmitters and interferents. The properties of the sensor combined with a microdialysis (MD) probe were also studied by measuring a solution containing a much higher concentration of Ch than ACh.

"Sol-gel-derived Cobalt Phthalocyanine-dispersed Carbon Composite Electrodes For Electrocatalysis And Amperometric Flow Detection"
Electroanalysis 1997 Volume 9, Issue 12 Pages 908-911
Joseph Wang*, Prasad V. A. Pamidi, Concepcion Parrado, Deog Su Park, Jose Pingarron

Abstract: A new sol-gel-derived electrocatalytic carbon composite electrode was prepared by dispersing cobalt phthalocyanine (CoPC) in a carbon ceramic network. The performance of the CoPC-modified sol-gel carbon composite electrode compares favorably with that of common CoPC-containing carbon pastes in term of electrocatalytic properties and short- and long-term stability. The greatly improved stability and electrocatalytic action are illustrated in cyclic-voltammetric and flow injection amperometric measurements of hydrogen peroxide, hydrazine, oxalic acid, cysteine and thiourea. Such improvements are coupled with the versatility, mechanical stability and renewability features of sol-gel carbon composites.

"Potentiometric Detection Of Metal-ions Separated By Liquid-chromatography Using A Tungsten-oxide Electrode"
Electroanalysis 1997 Volume 9, Issue 11 Pages 818-821
Zuliang Chen *, Peter W. Alexander

Abstract: The use of a tungsten oxide sensor for the potentiometric detection of metal ions separated by liquid chromatography is described. Separation of metal ions such as Fe3+, Fe2+. Cu2+ and Pb2+ was performed by ion chromatography using a mobile phase containing 25 mM sodium tartrate/2 mM ethylenediamine at pH 3.8. Calibration plots were linear in the range 0.5 to 3.5 mM. Potentiometric detection was also applied to ion-interaction chromatography. The results showed that separation of metal ions was improved and the detection limits for the test metals in the range of 0.5-5 nmol were obtained in the presence of sodium citrate/1-octanesulfonic acid at pH 3.0. The potentiometric detection described in this article is shown to base advantages in terms of low cost, simplicity and sensitivity. 23 References
Iron(III) Iron(2+) Copper(II) Lead(2+) HPIC Electrode Potentiometry Interferences

"A Photo-cured Coated Wire Potassium Ion-selective Electrode For Use In Flow Injection Potentiometry"
Electroanalysis 1997 Volume 9, Issue 11 Pages 813-817
Peter W. Alexander*, Telis Dimitrakopoulos, D. Brynn Hibbert

Abstract: A potassium ion selective electrode (ISE) is reported based on the epoxyacrylate polymer prepared from o-nitrophenyl octyl ether as the plasticizer and 2,2'-bis <3,4-(15-crown-5-)-2-nitrophenylcarbamoxymethyl>tetradecane (BME-44) as the ionophore. Several different electrodes were studied by photo-curing different membranes onto a silver wire (0.8 mm i.d.), and the response characteristics were evaluated. The membranes prepared exhibited strong adhesion to the metal substrate and showed improved mechanical strength compared to poly(vinyl chloride)-based membranes. The sensor exhibited Nernstian response over a log-linear range of between 0.01 mM and 100 mM, and was selective against the common interfering ions. Fast response reaching 90% of steady-state value in 5 s makes this sensor applicable for flow injection potentiometry measurements. The potassium ISE allows for accurate determinations of potassium in various water samples by flow injection potentiometry. 23 References
Potassium Water Potentiometry Electrode Electrode Electrode Selectivity Interferences

"Separation Of The Depolarizer From Surface-active Substances In The Tubes Of A Flow Injection System"
Electroanalysis 1997 Volume 9, Issue 10 Pages 781-787
Wladyslaw W. Kubiak*, Miroslaw M. Strozik

Abstract: The possibility to separate depolarizer and surfactant bands directly in a flow injection system is reported. Transport of a surfactant is according to an adsorptive or a hydrodynamic mechanism. In the former case a surfactant is transported slower than a depolarizer whereas in the latter case it is transported faster than a depolarizer. Theoretical background for both mechanisms is provided. The influence of sample volume, mixing coil parameters (tube length and inner diameter), tube material and flow rate on the separation process is discussed. The separation process dependence on the flow rate may provide the basis of surface active substances characterization. Such characteristics for several surfactants are presented. Under optimized conditions the parameters of the calibration plots for a depolarizer in the absence and presence of surfactant are statistically equivalent. 18 References
Surfactants Cadmium Amperometry Optimization Theory

"Controlling The Selectivity Of Glassy Carbon Flow Detectors Using Covalently Attached Monolayers"
Electroanalysis 1997 Volume 9, Issue 9 Pages 693-698
Alison J. Downard*, Alisa D. Roddick

Abstract: Significant improvements in selectivity for amperometric detection in flow analysis are achieved at covalently modified glassy carbon electrodes. Flow detectors modified with p-alkylbenzene (alkyl = methyl, decyl) and p-phenylacetate monolayers demonstrate how selectivity may be obtained on the basis of solute hydrophobicity and charge. The modified electrodes are stable under hydrodynamic conditions and in aqueous and mixed aqueous/organic carrier streams.

"Electrochemical Oxidation And Determination Of Heparin At Electrodes Modified With Ruthenium Oxide Or Copper Oxide"
Electroanalysis 1997 Volume 9, Issue 9 Pages 675-684
Krzysztof Lewinski, Yun Hu, Charles C. Griffin, James A. Cox

Abstract: The electrochemical oxidation of full-size heparin (13-15 kDa) is demonstrated in 1 M H-3PO-4 at a glassy carbon electrode coated with a ruthenium oxide film. The pathway apparently is analogous to chemical oxidation by periodate. By comparison to currents from inorganic species. it is apparent that only about 2 electrons per mole are involved. Flow injection analysis (FIA) allowed determinations down to 2 µM heparin, but the calibration plot was nonlinear. Low molecular weight heparin (5-6 kDa) was not electroactive with this system. In basic solution at a glassy carbon electrode that is modified with a film of Cu-2O, both full-size and low molecular weight heparin are oxidized. The pathways involved oxidative desulfation and attack on saccharide units with evolution of CO-2. Linear calibration plots which extended into the sub µM level were obtained by FIA. The detection limits, which were based on a value of 3 for the ratio of the signal to the standard deviation of replicates, were 9 nM for full-size and 20-30 nM for various low molecular weight heparin samples.
Heparin Electrode Electrode Potentiometry Apparatus Detector

"Voltammetric Behaviour And Ion-chromatographic Detection Of Nitrite At A Dispersed-platinum Glassy-carbon Electrode"
Electroanalysis 1997 Volume 9, Issue 8 Pages 596-601
Innocenzo G. Casella*, Anna M. Salvi

Abstract: The electrode was prepared by depositing 10 µL of 10 mM PtCl4 onto the surface of a glassy carbon electrode and drying at 40°C for 30 min. The electrode was conditioned in 0.1 M NaH2PO4 by cycling the potential between -0.3 and 1.3 V using a SCE reference electrode and a Pt foil counter electrode. Cyclic voltammograms were recorded over the same potential range at a scan rate of 50 mV/s. No significant interferences were observed in the presence of SDS, BSA, chloride, glycine, acetaldehyde, nitrate, sulfate, acetate and lactose. The electrode was used as an amperometric sensor for FIA systems and ion-chromatographic separations using an applied potential of 1.1 V. The detection limit was 15 nM. Calibration graphs were linear up to 0.5 mM. The method was used for the analysis of milk and pear juice. Recoveries were >85%.
Nitrite Milk Juice Amperometry Electrode Electrode Voltammetry Interferences

"The Determination Of Ethanol In Wine By Voltammetry With An Internal Standard"
Electroanalysis 1997 Volume 9, Issue 7 Pages 544-548
Ji Jin Yu, Weiguang Huang, D. Brynn Hibbert*

Abstract: A rapid method for the electroanalysis of ethanol is presented that incorporates flow extraction at room temperature, with voltammetric detection and potassium ferrocyanide as internal standard. in 0.1 M NaOH electrolyte, ethanol was oxidized at a platinum comb-shaped working electrode at -300 mV (vs. a Ag/AgCl reference electrode) and K4Fe(CN)(6) was oxidized at +180 mV. The ratio of the anodic peak currents was Linear with ethanol concentration in the range of 0.1 to 8.0% (v./v.), and the detection limit (calculated as 3s background) was 0.012 % (v./v.) for Osteryoung square wave voltammetry (OSWV) and 0.023 %(v./v.) for cyclic voltammetry (CV). The average extraction efficiency of ethanol from aqueous solutions, at 20±1°C, was 8.5%. The repeatability was in the range of 2.5 to 3.3% RSD (n = 8), and accuracy was in the range of 95.2 to 104.7% for the determination of wine samples. Application to wines compared well with GC and HPLC methods and the nominal ethanol concentration determined by gravimetry. Analytical parameters in CV and OSWV are optimized, and the dependence of the extraction efficiency with temperature and nitrogen gas flow is presented. 20 References
Ethanol Wine Amperometry Voltammetry Electrode Sample preparation Extraction Optimization Method comparison

"Flow Injection, Amperometric Determination Of Ethanol In Wines After Solid-phase Extraction"
Electroanalysis 1997 Volume 9, Issue 7 Pages 541-543
Zuliang Chen, Ji Jin Yu, D. Brynn Hibbert*

Abstract: Wine (0.5 ml) was diluted with water (1 ml) and purified on a Super Clean LC-SAX anion exchange-cartridge by elution with 2 mL water. A portion of the eluate was injected into a stream (0.5 ml/min) of 0.1 M NaOH of a FIA system. Detection was effected with a Ni wire working electrode, a Ag/AgCl reference electrode and a Pt wire counter electrode. A potential of +0.6 V was applied to the working electrode. The detection limit was 1 µM-ethanol. The response was linear up to 1 mM. Recoveries ranged from 100.8-102.9%.
Ethanol Wine Amperometry Electrode Ion exchange Sample preparation Extraction

"Layer-layer Assembly For Extremely Stable Glucose Sensors"
Electroanalysis 1997 Volume 9, Issue 7 Pages 533-536
Golam Faruque Khan

Abstract: The sensor was fabricated from a shapable electro-conductive film surface, onto which a suspension of Pt black particles in 2-methoxyethanol was deposited. The solvent was removed by heating at 60°C in vacuo and the resulting coated film was pressed between hot steel rollers heated to 150°C. The film was cut to the desired dimensions and glucose oxidase was immobilized by applying a solution of the enzyme in PBS of pH 7 and allowing it to evaporate at room temperature. A 5% gelatin solution was spread over the enzyme layer and allowed to dry. The electrode was dipped into a 5% glutaraldehyde solution and dried for several hours at room temperature. A disk of 3.5 mm diameter was cut and mounted at the opening of a flow-cell. The sensor disk was covered with a hydrophilic polycarbonate membrane. The response of the sensor for glucose was studied in a FIA system at 37°C using 0.1 M PBS of pH 7 as the carrier solution (0.2 ml/min). A potential of 0.4 V was applied to the sensor relative to a Ag/AgCl reference electrode. A stainless steel electrode served as the counter electrode. The electrode was stable for at least 50 days of continuous operation. Response was linear up to 40 mM.
Glucose Sensor Electrode Electrode Electrode Detector

"An Amperometric Lactate Sensor Based On A NAD+-analogue And Lactate Dehydrogenase Coimmobilized On Reticulated Vitreous Carbon"
Electroanalysis 1997 Volume 9, Issue 7 Pages 523-526
Masoud Khayyami, Nuria Pe&ntilde;a Garcia, Per-Olof Larsson, Bengt Danielsson, Gillis Johansson *

Abstract: The sensor was fabricated from a reticulated vitreous C cylinder previously treated with 6 M HCl for 1 h. After rinsing successively with water and methanol, the dried cylinder was fitted into a glass tubing through which a 4% solution of 1-cyclohexyl-3-(2-morpholinoethyl)carbodi-imide metho-p-toluenesulfonate in 50 mM acetate buffer of pH 5.1 was circulated for 2.5 h at 0.2 ml/min. A solution containing 60 mg of lactate dehydrogenase and 60 mg of N6-[(2-aminoethyl)carbamoylmethyl]-NAD+ in the same acetate buffer was circulated for 3 h at 1-2°C. The response of the electrode for lactate was investigated by FIA. The electrode was placed into a piece of glass tubing, which contained an uncoated reticulated vitreous C cylinder as counter electrode; the two electrodes were separated from each other by means of a nylon net. Measurements were made with an applied potential of +400 mV relative to a Ag/AgCl reference electrode, which was placed downstream. The carrier solution consisted of 0.1 M phosphate buffer of pH 7.5. Response was linear up to 0.5 mM. The stability of the electrode was improved by the addition of 5 µM-Meldola blue to the carrier solution and by decreasing the applied potential to -0.1 V.
Lactate Amperometry Electrode Electrode Sensor Buffer

"Continuous-flow And Flow Injection Stripping-voltammetric Determination Of Silver(I), Mercury(II) And Bismuth(III) At A Bulk Modified Graphite-tube Electrode"
Electroanalysis 1997 Volume 9, Issue 6 Pages 481-489
Ruidong Ye, Soo Beng Khoo*

Abstract: In continuous-flow analysis (CFA) sample solution [in 0.1 M acetate medium of pH 4.32, 0.1 M phosphate buffer of pH 5.5, and Britton-Robinson buffer of pH 3.8 for Ag(I), Hg(II), and Bi(III), respectively] was pumped through the flow cell for 10 min at 1.41 ml/min and accumulation was carried out under open circuit conditions. Then deaerated stripping solution [70 mM HCl, 75 mM KBr, 100 mM HNO3, and 1 M HCl for Ag(I), Hg(II), and Bi(III), respectively] was passed through the cell at 0.72 ml/min and after 15 s the appropriate deposition potential was applied [-0.15, -0.20, and -0.50 V (vs. Ag/AgCl) for Ag, Hg and Bi, respectively] for 15 s. Finally, differential-pulse anodic-stripping was carried out commencing at the deposition potential of the metal. For FIA (details given), the analysis was very similar and calibration graphs (CG) were linear for 5 nM- to 1 µM-Ag(I), 10 nM- to 2 µM-Hg(II) and 100 nM- to 5 µM-Bi(III). The respective detection limits (DL) were 0.18, 1.9 and 9.5 nM; RSD (n = 6) were 2.53-10.5, 2.57-5.77 and 5.97-7.9%, respectively. For FIA, CG were linear from 50 nM- to 5 µM-Ag(I), 100 nM- to 5 µM-Hg(II), and 5-50 µM-Bi(III), and the respective DL were 11, 20 and 1200 nM. RSD (n = 6) were 6.32, 6.44 and 7.9%, respectively.
Silver(I) Mercury(II) Bismuth(3+) Sea Urine Voltammetry Electrode Electrode

"Conducting Polymer Sensors For The Amperometric Detection Of Proteins In A Flow System: Use Of Sulfonated Dye Counterions To Induce Selectivity"
Electroanalysis 1997 Volume 9, Issue 6 Pages 454-460
W. Lu, Gordon G. Wallace*

Abstract: Polymer-coated Pt electrodes were prepared with the incorporation of either Methyl orange (I), Bromocresol green (II), Bromocresol purple (III), or brilliant blue R (IV) into the polymer matrix by galvanostatic polymerization of solutions containing 0.2 M pyrrole and 5 mM sulfonated dye for 10 s at a current density of 2 mA/cm2, and the resulting electrodes were evaluated for use in the determination of proteins by flow injection voltammetry. The sensitivity and selectivity of the response for individual proteins varied with pH and with the dye incorporated into the polymer matrix. Optimum eluents were 0.1 M sodium phosphate (pH 5), 75 mM sodium succinate (pH 7), 0.1 M sodium acetate (pH 6) and 0.87-M-H3PO4 in 47 g/L ethanol for electrodes incorporating I, II, III and IV respectively. In the detection of BSA at a I-coated electrode at an applied potential of 1 V, the detection limit was 4.8 nM, the electrode response was linear over two orders of magnitude, and the RSD was 2.2% (n = 10). With continuous operation over a period of 5 h the electrode response decreased by 6.5%, but there was no further deterioration in performance after storage in eluent for five or six days. In this article, we have demonstrated the feasibility of using dye binding interactions for the amperometric detection of proteins at conducting polymer coated electrodes with flow injection analysis. Incorporation of appropriate dyes into the conducting polymer during synthesis enables sensitive and selective responses to be obtained. The effects of eluent pH and applied potential on the responses obtained for a range of proteins have been investigated. These parameters can be used to modify selectivity and achieve sensitivity. 24 References
Proteins Amperometry Voltammetry Electrode Sensor Selectivity

"TTF-TCNQ-complex-based Printed Biosensor For Long-term Operation"
Electroanalysis 1997 Volume 9, Issue 4 Pages 325-329
Golam Faruque Khan

Abstract: Crystals of the TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) complex were soaked overnight in glucose oxidase solution in PBS to immobilize the enzyme, filtered off, dried under reduced pressure, and mixed with polyisobutene solution in heptane or polyester binder solution in 2-(2-butoxyethoxy) ethyl acetate. The resulting paste was packed into the cavity of a flow-through cell equipped with an integrated ceramic-based chip incorporating working, reference and counter electrodes. Alternatively, the paste was applied to the Pt-coated working part of the chip and dried under reduced pressure. In either instance, 5% gelatin solution was spread over the sensitive area and dried at ambient temperature, and the assembly was then dipped in 5% glutaraldehyde solution for 1 min, rinsed with water and dried at room temperature. The response of the biosensors to glucose was evaluated in a flow injection system with PBS of pH 7 as the carrier solution (0.1 ml/min). Measurements were made at 37°C with an applied potential of 0.15 V. The cavity-type biosensor exhibited better sensitivity, linearity of response and stability than the planar biosensor.
Glucose Sensor Electrode Electrode Sensitivity

"Critical Comparison Of Metallized And Mediator-based Carbon-paste Glucose Biosensors"
Electroanalysis 1997 Volume 9, Issue 4 Pages 298-301
Joseph Wang*, Liang Chen, Jie Liu

Abstract: Metallized carbon-paste electrodes were prepared by packing a portion of a mixture of 40 mg of 5% Rh on carbon, 60 mg of mineral oil, 10 mg of glucose oxidase and the desired amount of PEI into the cavity of a PTFE electrode body. A steel screw was used to provide electrical contact. The mediator-based carbon-paste electrodes were prepared similarly except that 3 mg of 1,1'-dimethylferrocene was added to the paste. The characteristics of the two electrodes were compared by performing amperometric and cyclic voltammetric measurements in 50 mM phosphate buffer of pH 7.4 as supporting electrolyte with an Ag/AgCl reference and a Pt-wire counter electrode. The effect of the loading of PEI on the response of the electrodes is reported. Under optimum conditions, calibration graphs were linear up to 10 mM for the metallized electrode and 8 mM for the mediator-based electrode. The detection limits under flow injection conditions were 30 µM and 22 µM, respectively.
Glucose Fluorescence Biamperometry Amperometry Electrode Voltammetry Sensor Method comparison Optimization Buffer

"The Coulometric Determination Of Chemical Oxygen-demand"
Electroanalysis 1997 Volume 9, Issue 4 Pages 279-283
Kim L. Pamplin, Dennis C. Johnson*

Abstract: The chemical oxygen demand (COD) of solutions containing various organic compounds is calculated from the net faradaic charge (Q(net)) estimated for the total electrolytic oxidation of Cr-III generated during oxidative degradation of the organic compounds in acidic media containing excess Cr-VI. Values of Q(net) for conversion of Cr-III to Cr-VI are estimated from the linearized chronoamperometric data plotted as ln i(tot,t) vs. t. This procedure is preferred over determinations of Q(net) from the total integrals of i(tot) over the entire electrolysis period because of large errors that can result from uncertainty in the background current (i(bkg)) for t --> infinity. The proposed coulometric procedure offers the benefit that reagent solutions can be reused, thereby minimizing the need for disposal of wastes containing toxic Cr-VI. This procedure was applied in a single digest solution for consecutive determinations of COD. Average COD values for potassium acid phthalate and glucose were 103.8 % (s = 6.0, N = 10) and 100.2 % (s = 4.2, N = 11), respectively, based on the theoretical degradation to CO2. In comparison for these same samples, an EPA approved method, based on colorimetric determination of Cr-III, gave COD values of 101.4 % (S = 1.4, N = 5) and 100.1 % (s = 1.4, N = 5) of the theoretical. Statistical tests indicate no significant difference in the COD values determined for these compounds using the coulometric and EPA methods. 30 References
Chemical oxygen demand Water Coulometry Method comparison Redox

"Simultaneous FIA Determination Of Two Components With Differential Normal Pulse Voltammetric Multidetection"
Electroanalysis 1997 Volume 9, Issue 3 Pages 247-250
es&uacute;s Alp&iacute;zar, Antonio Cresp&iacute;, Andreu Cladera, Rafael Forteza, V&iacute;ctor Cerd&agrave; *

Abstract: The method was applied for the determination of ammonium ferrous sulfate and p-aminophenol. The sample solution (200 µL) was injected into a carrier stream of 50 mM H2SO4 (1.2 ml/min), which was pumped through a flow-through cell equipped with a carbon paste working electrode, a Ag/AgCl reference electrode and a glassy carbon counter electrode. Two sequential pulses of 50 mV amplitude, 100 ms pulse width and 850 ms pulse interval were applied to the working electrode; the two pulses were preceeded by applied potentials of 200 mV and 900 mV, respectively. Complete separation of the analytes was possible by proper choice of the prepulse potentials and pulse amplitudes. Calibration graphs were linear up to 12 µg/ml for both analytes.
Iron(2+) 4-Aminophenol Amperometry Electrode Voltammetry Simultaneous analysis

"Amperometry And Cyclic Voltammetry Of Tyrosine And Tryptophan-containing Oligopeptides At Carbon-fibre Microelectrodes Applied To Single-cell Analysis"
Electroanalysis 1997 Volume 9, Issue 3 Pages 203-208
Charina D. Paras, Robert T. Kennedy*

Abstract: The electrode was prepared by inserting a 9 µm carbon fiber inside a glass capillary which was then pulled to a fine tip. The carbon fiber was kept in place by immersing the capillary tip in epoxy. After polishing the electrode surface, FIA measurements were made at a potential of 0.8 V vs. SCE using 60 mM phosphate buffer of pH 7.4 as the carrier stream (1.5 ml/min). Melanocytes were isolated from the pituitary neurointermediate lobe and the peptide hormones were extracted, incubated (details given) and determined. The stability of the electrode was improved by electrochemical pretreatment involving potential scanning from -1.0 to +1.0 V at 300 V/s for 2 min. Selectivity of the peptides was achieved by cyclic voltammetry over the range 0 to 1.2 V using a scan rate of 800 V/s. The experimental parameters were optimized for the detection of the melanocyte-stimulating hormone secreted from single melanocytes during exocytosis.
Peptides, oligo Cell Amperometry Voltammetry Electrode Buffer Selectivity Optimization

"Amperometric Biosensors Based On NAD(P)-dependent Dehydrogenase Enzymes"
Electroanalysis 1997 Volume 9, Issue 3 Pages 191-202
Maria Jes&uacute;s Lobo, Arturo J. Miranda, Paulino Tu&ntilde;&oacute;n

Abstract: This review deals with the use of pyridine-nucleotide dependent dehydrogenase enzymes in amperometric biosensor design. The electrochemistry of the nicotinamide coenzymes, their mechanism and the challenges associated with their direct oxidation on solid electrodes are discussed. In addition, a survey of the different solutions proposed in the literature for addressing these problems and some of their applications are presented. 175 References
Whole Amperometry Sensor Electrode Immobilized enzyme Review

"Evaluation Of A New Wall-jet Flow-through Cell For Commercial Ion-selective Electrodes In Flow Injection Potentiometry"
Electroanalysis 1997 Volume 9, Issue 2 Pages 179-182
Lucy Tina Di Benedetto, Telis Dimitrakopoulos*

Abstract: The cited poly(methyl methacrylate) cell (28 x 25 x 35 mm) which can accommodate commercial gas-sensing, liquid polymer membrane and solid-state-based ISE is described (diagram given). The cell contains a 1 mm i.d. Ag/AgCl wire reference electrode and the dead volume of the ISE compartment is 18 µL. Two separate inlets and flow channels are used to carry the sample and reference solutions to the ISE and reference electrode, respectively, after which the streams are merged and carried to waste. The analysis rate was up to 240 samples/h and injection volumes >=50 µL are recommended. An Orion 95-12 ammonia ISE was used in the cell with a sample injection volume of 100 µL and 1 M KOH/1 µM-NH4Cl and 1 M KCl as carrier and reference solutions, respectively, e.g., at total flow rate of 1.8 ml/min. Calibration graphs of potential vs. log. NH3 concentration were linear for 0.1-10 mM NH3 and peak height RSD were 0.4-3.5%. The flow cell was also used to determine Ca and iodide using appropriate ISE.
Ammonium Calcium(2+) Iodide Potentiometry Electrode Electrode Flowcell Apparatus

"Square-wave Adsorptive Stripping Voltammetry Of Nickel(II) In Flowing Systems At A Wall-jet Mercury-film Electrode Plated In Situ"
Electroanalysis 1997 Volume 9, Issue 2 Pages 145-149
Maria M. G. S. Rocha*, Maria M. P. M. Neto, Maria Odete Torres, Amarilis de Varennes

Abstract: In a voltammetric cell the sample solution was pumped at 45 nl/s into 0.1 M KNO3/50 µM-mercury(II) nitrate/0.2 mM dimethylglyoxime with pH adjusted to 9 with KOH. The cell also contains a 0.327 cm2 glassy C disc wall-jet electrode 3 cm from the sample inlet, a saturated KCl/Ag/AgCl reference electrode and a Pt tube counter electrode and cell outlet. The Hg and Ni-dimethylglyoxime complex were adsorbed for 1 min onto the wall-jet electrode at -0.8 V vs. reference electrode before square-wave stripping voltammetry in the negative direction at an amplitude of 50 mV, a frequency of 60 Hz and a step of 5 mV. After 1 h use, the wall-jet electrode was cleaned for 1 min at +0.4 V. Calibration graphs were linear for 0.8 nM to 0.25 µM-Ni(II) with a detection limit of 130 pM. There was no interference from a 10 000-fold excess of Cr(III), Fe(III), Co(II), Cd(II), Hg(II) and Pb(II) but a 5000- and 3000-fold excess of Zn(II) and Mn(II), respectively, interfered. The use of standard additions is recommended for quantification. The method should be useful for the continuous online monitoring of Ni.
Nickel(II) Voltammetry Electrode Electrode Electrode Interferences Standard additions calibration

"Flow Injection Potentiometric Detection Of Metal-ions Based On Tungsten-oxide Electrode"
Electroanalysis 1997 Volume 9, Issue 2 Pages 141-144
Zuliang Chen, Peter W. Alexander

Abstract: The use of a tungsten oxide electrode for potentiometric flow injection analysis of transition metal ions is described. The effect of a variety of experimental conditions, including the carrier pH, the types of ligands and their concentrations, was studied. It was found that the best sensitivity for the ions tested was obtained using EDTA as a ligand. The electrode exhibited a linear response for Fe3+, Cu2+, Pb2+ and Ca2+ in the range of 2.5 x 10^-4 M to 2 x 10^-3 M using with 1 x 10^-3 M EDTA at pH 5.0 as carrier. The detection limits were found to be between 1 x 10^-5 to 5 x 10^-5 M. Reproducibility for Fe3+ was about 1.7% with a stable baseline potential. The method is based on the use of the FIA system of Alexander et al. (Anal. Lett., 1984, 17, 3 09) for the indirect determination of metals at a tungsten oxide wire electrode after complexation with EDTA. Sample (10 µL) was injected into a stream of 0.5 ml/min 1 mM EDTA with pH adjusted to 5 with 1 mM NaOH and Ag/AgCl as reference electrode. Calibration graphs were linear for 0.25-2 mM Fe3+, Cu2+, Pb2+ and Ca2+ with detection limits of 1, 50, 50 and 10 µM, respectively. In the determination of 1 mM Fe3+, the peak height RSD was 1.7% (n = 10). The effects of varying complexing agent molecule and concentration, carrier pH and flow rate on the determinations were studied. The results are compared with those obtained at a Cu electrode. 20 References
Calcium(2+) Copper(II) Iron(III) Lead(2+) Potentiometry Electrode Voltammetry EDTA Method comparison Optimization Complexation

"Electrocatalytic Reduction Of Haemoglobin At A Chemically Modified Electrode Containing Riboflavin"
Electroanalysis 1997 Volume 9, Issue 2 Pages 115-119
Wenliang Sun, Jilie Kong, And Jiaqi Deng

Abstract: The electrode was constructed from the end face of a 5 mm diameter graphite rod enclosed in a Plexiglass tube. The exposed rod face was polished with emery paper, rinsed with water, sonicated successively in 1:1 HNO3, acetone and water and immersed for 6 h in 0.1 mM riboflavin (I) in buffer of pH 6.1. Cyclic voltammograms of the electrode in KH2PO4/Na2HPO4 buffer of pH 6.8 showed two symmetrical I reduction and oxidation peaks with E1/2 -0.37 V vs. a saturated Ag/AgCl reference electrode. A Pt-wire auxiliary electrode was used and solutions were deaerated with N2 for 15 min before voltammetry. After 30 min continuous use at pH 6.8 the electrode activity was 60% of the original value. In the presence of haemoglobin (II) the I reduction and oxidation peak heights were increased and decreased, respectively, because of electron transfer between I and II. Calibration graphs obtained at scan rate of 50 mV/s were linear for 30-480 µM-II. The effect of pH on electrode catalytic activity was studied. The electrodes may be useful for FIA and analyzing other proteins.
Hemoglobin Voltammetry Electrode Electrode Optimization pH

"Detection Of Hydrogen Peroxide And Other Molecules Of Biological Importance At An Electrocatalytic Surface On A Carbon Fibre Microelectrode"
Electroanalysis 1997 Volume 9, Issue 2 Pages 102-109
Wilbur B. Nowall, Werner G. Kuhr*

Abstract: The electrocatalytic oxidation of hydrogen peroxide in solution at a modified carbon fiber electrode has been investigated. A simple electrochemical procedure has been developed to dramatically improve the voltammetry for the oxidation of peroxide, NADH, and several other species under steady state and fast scan voltammetry. The surface is generated by the electrochemical oxidation of NADH followed by exposure to peroxide. This procedure yields a surface which is sensitive to peroxide and stable in air for more than 90 days. This oxidation occurs at a potential such that it is easily discriminated from the analytes tested in this study. The tapered tip of a 32 µm diameter C fiber electrode was exposed to a stream of H2O-saturated air before and after polishing with 1000-grit sandpaper for 10 s. The tip was subjected to sine wave excitation from 0.1-1.1 V at 50 Hz, 600 mV bias and 38°C in phosphate buffer of pH 7.4 with ten 5 s injections of 100 µM-NADH followed by 1 mM H2O2. The injections were made at 1 min intervals. The electrode was used with phosphate buffer of pH 7.4 as supporting electrolyte and a Ag/AgCl reference electrode. At a scan rate 10 mV/s E1/2 for H2O2 was >1.1 V and there was no interference from NADH, ascorbate, dopamine, 3,4-dihydroxyphenylacetic acid and uric acid (E1/2 = +290, -25, +60, +110 and +225 mV, respectively) which could also be determined at the electrode. The electrode response to these compounds was also studied at 100 V/s at which calibration graphs were linear from the detection limit (1 µM) to 10 mM H2O2. The electrode was stable in air for >90 days and the response time was a few hundred ms. H2O2 may be useful as a diffusive redox mediator for immobilized oxidases. The electrode may also be useful for in situ and FIA applications. 50 References
Hydrogen peroxide Voltammetry Electrode In vivo monitoring Heated reaction Interferences Buffer Steady state

"A Study In The Use Of An Extrapolation Method To Find The Equilibrium Potential For Certain Ion-selective Electrodes"
Electroanalysis 1997 Volume 9, Issue 1 Pages 85-86
Peter J. Watkins*

Abstract: The equivalent potentials for certain ion-selective electrodes (lead, cadmium, iodide, chloride, nitrate) are found by an extrapolation method, rather than wait for the steady-state potential to be reached.

"Flow Characteristics Of A Versatile Wall-jet Or Radial-flow Thin-layer Large-volume Cell For Electrochemical Detection In Flow-through Analytical Systems"
Electroanalysis 1997 Volume 9, Issue 1 Pages 32-39
Beno&icirc;t Soucaze-Guillous, Wodzimierz Kutner

Abstract: Several previously used cell designs were incorporated into the cited 35 mL amperometric or voltammetric cell (diagram and description given). The cell had an interchangeable disc, ring-disc and microdisc working electrodes, a NaCl-saturated Ag/AgCl reference electrode, a Pt wire auxiliary electrode, interchangeable flat and conical inlet capillary nozzles and a micrometer screw for adjusting the distance between the inlet and working electrode (>=10 µm). The operating mode of the cell (radial-flow, wall-jet or wall-tube) was chosen by inserting an appropriate working electrode and inlet nozzle, and adjusting the gap between the nozzle and the working electrode. The flow characteristics of the cell were studied using a 4 mm diameter Ag, a 10 µm diameter Pt and a Au-Au ring-disc working electrode. The cell was used to detect nitrophenol and aniline isomers after analytical and microbore HPLC and for the electrocatalytic FIA detection of benzyl alcohol (conditions given). The cell may also be useful in the wall-jet configuration for HPLC post-column derivatization and detection. The advantages and some other possible uses of the cell are discussed.
Aniline Phenols, nitro Alcohols HPLC Amperometry Voltammetry Electrode Flowcell Apparatus

"Square-wave Adsorptive-stripping Voltammetry Of Nickel And Cobalt At Wall-jet Electrodes In Continuous-flow"
Electroanalysis 1996 Volume 8, Issue 12 Pages 1169-1173
Christopher M. A. Brett*, M. Beatriz Quinaz Garcia, Jos&eacute; L. F. C. Lima

Abstract: The wall-jet cell was equipped with a glassy C working electrode, a Pt tube counter electrode placed in the cell exit and a Ag/AgCl reference electrode placed in a compartment separated by a porous glass frit. Before determination, a Hg thin film was deposited onto the working electrode surface by passing a solution containing 0.1 mM Hg2+ in 0.1 M KNO3/5 mM HNO3 or in the carrier solution used for the determination; a potential of -1 V was applied for 300 s. The analyte solution was added to the carrier solution consisting of 30 mM sodium N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonate]/ 0.1 M NaClO4 and the mixture was pumped at 0.045 ml/s through the system. Determination was effected by applying a deposition potential of -0.7 V for 60 s, followed by scanning to -1.2 V, operated in the square wave mode with an amplitude of 30 mV and a frequency of 100 Hz. Detection limits were 1 nM for both analytes. Calibration plots were linear up to 0.1 µM in both instances.
Cobalt Nickel Voltammetry Voltammetry

"Entrapment Of Enzymes In Electropolymers For Biosensors And Graphite Felt Based Flow-through Enzyme Reactors"
Electroanalysis 1996 Volume 8, Issue 12 Pages 1135-1139
Ulrich R&uuml;del*, Oliver Geschke, Karl Cammann

Abstract: Immobilization of glucose oxidase in conducting polymers electrochemically generated from pyrrole, N-methylpyrrole, aniline and ortho-phenylene diamine on platinum surfaces was used to construct amperometric glucose biosensors. High sensitivity was obtained with a sensor utilizing polymerized o-phenylene diamine as entrapment matrix. This polymer, as well as polypyrrole, was used to prepare a new type of enzyme reactors with immobilized glucose or lactate oxidase by depositing enzyme-polymer layers on pieces of graphite felt. Mounted into a column, the felt can then be applied as an enzyme reactor in a flow system. It can either be used as working electrode itself in an electrochemical detection system or be combined with a separate detector. A microelectrode array was chosen as an example of the latter. With this system, detection limits lower than 500 M and a linear range up to 10 mM were obtained for glucose and a detection limit lower than 50 M and a linear range up to I mM for lactate, respectively.

"Enhanced Selectivity And Sensitivity Of First-generation Enzyme Electrodes Based On The Coupling Of Rhodinized Carbon-paste Transducers And Permselective Poly(o-phenylenediamine) Coatings"
Electroanalysis 1996 Volume 8, Issue 12 Pages 1127-1130
Joseph Wang *, Liang Chen, Jie Liu, Fang Lu

Abstract: Glucose oxidase (10 mg) was mixed with rhodium-containing C paste (100 mg) and a portion of the resulting paste was packed into the cavity of a PTFE sleeve. Electropolymerization was performed in a solution of 50 mM phosphate buffer of pH 6 containing 5 mM 1,3-phenylenediamine by applying a potential of +0.65 V for 20 min. The response of the electrode for glucose was investigated in batch and flow injection experiments. Using the latter technique, the detection limit was 0.1 mM. The response was linear up to 5 mM.
Glucose Sensor

"Effect Of HY-zeolites On The Performance Of Tyrosinase-modified Carbon-paste Electrodes"
Electroanalysis 1996 Volume 8, Issue 12 Pages 1121-1126
Gy&ouml;rgy Marko-Varga *, Elisabeth Burestedt, Carl Johan Svensson, Jenny Emn&eacute;us, Lo Gorton, Tautgirdas Ruzgas, Mareike Lutz, Klaus K. Unger

Abstract: Tyrosinase-modified graphite pastes containing varying amounts of HY-zeolite 6, 25, 56 and 200 were prepared either by simple mixing or by adsorption of the enzyme on the zeolite particles. The performance of the electrodes were investigated by cyclic voltammetry of 1 mM catechol in 0.25 M phosphate buffer of pH 7 using SCE as reference electrode and a Pt-wire electrode as the counter electrode. The potential was cycled from -0.2 to 0.5 V at 0.05 V/s. FIA measurements were performed using 0.1 M phosphate buffer of pH 6 as the carrier solution and applying a potential of -0.05 V to the prepared electrode. Highest response was obtained with the electrode containing the most hydrophilic HY-zeolite 6 to which kanamycin was added.
Electrode Voltammetry

"Simultaneous Determination Of Chloride And Fluoride Ions In Waters By Sequential Injection Analysis"
Electroanalysis 1996 Volume 8, Issue 11 Pages 1051-1054
Jes&uacute;s Alp&iacute;zar, Antonio Cresp&iacute;, Andreu Cladera, Rafael Forteza, V&iacute;ctor Cerd&agrave;

Abstract: A sequential injection analysis (SIA) system was developed, based on chloride (I)-selective and fluoride (II)-selective electrodes placed in series, in conjunction with a Ag/AgCl reference electrode (diagram given). Water samples (0.2 ml) were subjected to SIA, sandwiched between 0.4 mL and 3.8 mL cyclohexane-1,2-diamine-NNN'N'-tetra-acetic acid as total ionic strength adjustment buffer, at a flow-rate of 4 ml/min and with potentiometric detection. Calibration graphs were linear from 20-500 µg/ml I and 0.5-200 µg/ml II. The RSD (n = 20) were 1% for 50 µg/ml I and 3.7% for 1 µg/ml II. Stopped-flow detection did not improve the results. The method was applied to potable water samples. The I results generally agreed with those obtained using a batch method and the Mohr method. Recoveries of II from spiked tap water were 92-109%.
Chloride Fluoride Water Potentiometry Electrode Electrode Electrode Sequential injection Method comparison Stopped-flow

"Peroxidase-modified Carbon-paste Microelectrode As Amperometric FI-detector For Peroxides In Partial Aqueous Media"
Electroanalysis 1996 Volume 8, Issue 11 Pages 1014-1019
Ionel C. Popescu, Elisabeth Cs&ouml;regi, Lo Gorton

Abstract: Portions (100 mg) of graphite powder were treated for 2 h at 4°C with 400 µL 0.1 M phosphate buffer (pH 8) containing 2 mg horseradish peroxidase (HP) or fungal peroxidase (from Arthromyces ramosus) and 10 mg lactitol. The mixtures were dried under reduced pressure, mixed with 40 µL paraffin oil, and the resulting pastes packed into PTFE tubes (10 cm x 0.5 mm i.d.) to give peroxidase/lactitol-modified C-paste electrodes. These were used in a flow injection system (details given) with Ag/AgCl quasi-reference and counter electrodes. For each type of peroxidase, enzymatic activity was higher for the detection of H2O2 (I) than for 2-butanone peroxide (II) regardless of the solvent composition. Detection limits were 0.1 µM I and 0.3 µM II, obtained with a HP-modified electrode. For both types of peroxidase the analytical sensitivity decreased according to solvent composition in the order water > aqueous 10% acetonitrile > aqueous 10% methanol (results presented).
Hydrogen peroxide Water Electrode Amperometry

"Flow Injection Analysis Of Ethanol With An Alcohol Dehydrogenase-modified Carbon Paste Electrode"
Electroanalysis 1996 Volume 8, Issue 10 Pages 932-937
M. Jesus Lobo, Arturo J. Miranda, Paulino Tu&ntilde;&oacute;n*

Abstract: An amperometric ethanol sensor based on carbon paste, chemically modified with alcohol dehydrogenase, nicotinamide adenine dinucleotide and Toluidine Blue O as a mediator, is described. The surface of the sensor is protected by covering with a dialysis membrane. Dialysis membranes with different molecular weight cut-off were tested for preventing leaching of soluble species from the electrode. The influence of various experimental conditions was investigated for optimum analytical performance. Linear responses for ethanol in the range 2 times 10^-5 M to 2.4 times 10^-4 M at 0.05 V (Ag/AgCl) and a response time of 60 s were obtained. The sensor was also used in flow injection analysis and tested on wine samples. Modified carbon paste was prepared from graphite powder/paraffin oil mixture containing 10% toluidine blue O, 5% alcohol dehydrogenase and 10% nicotinamide adenine dinucleotide. The paste was packed into the body of the working electrode and covered with a dialysis membrane. Cyclic voltammetric measurements were made in 0.1 M phosphate/citrate buffer of pH 8.5 with Ag/AgCl and a Pt wire electrode served as the reference and counter electrodes, respectively. Amperometric measurements for addition of suitable portions of standard ethanol (I) solutions were made at an applied potential of 50 mV. The calibration graph was linear up to 24 µmM I with a detection limit of 8.7 µM. FIA was effected with the supporting electrolyte buffer containing 0.7 M NaCl as the carrier solution (0.5 ml/min). The sensor was stable for, at least, 1 month.
Ethanol Wine Electrode Electrode Sensor Optimization Dialysis

"Flow Injection Monitoring And Analysis Of Mixtures Of Simazine, Atrazine And Propazine Using Filter-supported Bilayer Lipid Membranes"
Electroanalysis 1996 Volume 8, Issue 10 Pages 907-912
Dimitrios P. Nikolelis*, Christina C. Siontorou

Abstract: A microporous glass fiber disk (0.9 cm diameter) was mounted between two plastic layers having a central hole of 0.32 mm diameter. The whole was clamped between two Plexiglass chambers. One of the chambers contained a flow-through electrochemical cell, through which the carrier solution was pumped. A Ag/AgCl reference electrode was immersed in the waste of the carrier solution. The second chamber was equipped with a second Ag/AgCl reference electrode and a potential of 25 mV was applied between the two electrodes. Formation of stabilized BLM was effected by the method of Nikolelis et al. (Ibid.,1995, 7, 531 and Anal. Chem., 1995, 67 936), using solutions of lyophilized egg phosphatidylcholine and dipalmitoylphosphatidic aci d in hexane/ethanol (4:1). The carrier electrolyte solution consisted of 0.1 M KCl/10 mM HEPES buffer of pH 8 containing 1 mM calcium ions. The herbicide solutions were injected into the carrier stream and the resulting transient current signal was recorded. Calibration graphs were linear up to 1.4 ppm, 210 ppb and 300 ppb, respectively, for atrazine, simazine and propazine and the corresponding detection limits were 40, 8 and 20 ppb.
Atrazine Propazine Simazine Amperometry Electrode Buffer

"Flow-type Cyanide Sensor Using An Immobilized Micro-organism"
Electroanalysis 1996 Volume 8, Issue 10 Pages 876-879
Kazunori Ikebukuro, Masahiro Honda, Keijiro Nakanishi, Yoko Nomura, Yuzo Masuda, Kenji Yokoyama, Yoshihiro Yamauchi, Isao Karube *

Abstract: A suspension of Saccharomyces cerevisiae cells in 10 mM Tris buffer of pH 8 was prepared and immobilized onto a porous 0.45 µm cellulose nitrate membrane (experimental details given) and the membrane was attached to an oxygen electrode and covered with a dialysis membrane. The electrode was transferred to a flow injection system (schematic shown), in which a reagent solution containing 150 mg/l glucose at a temperature of 30°C was pumped at 0.5 ml/min. The analyte solution, containing suitable concentrations of cyanide (I), was injected into the carrier solution and the corresponding increase in current was recorded. The calibration was linear up to 15 µM I with a detection limit of 1.5 µM. A 10-fold improvement in sensitivity was achieved by immobilizing the cells onto porous glass beads, which were then packed into a syringe body to form a reactor. The reactor was mounted between two oxygen electrodes in a flow-through system (details given) and the difference in the amperometric response of the two electrodes was recorded. The latter system exhibited better sensitivity and was stable for, at least, 16 days.
Cyanide Sensor Dialysis Porous glass beads Immobilized cell Cellulose nitrate

"Determination Of Tin(II) In Pharmaceuticals By Amperometric Oxidation After Complexation With Tropolone"
Electroanalysis 1996 Volume 8, Issue 8-9 Pages 789-794
K. Boutakhrit, G. Quarin, S. A. &Ouml;zkan, J.-M. Kauffmann *

Abstract: Dental gel (2 g) was extracted with hot 1 M HCl (20 ml) by sonication for 5 min, and a portion of the extract was diluted with 50 mM acetate buffer of pH 5.5 containing 0.1 mM tropolone. A 20 µL portion of the mixture was injected into an FIA system comprising 50 mM acetate buffer of pH 5.5 as the carrier solution. The solution was pumped (0.8 ml/min) through a reaction coil (30 cm x 0.2 mm i.d.) to an electrochemical cell equipped with a vitreous-carbon working electrode, an Ag/AgCl reference electrode and a Pt-wire counter electrode. The working electrode potential was set at +0.1 V. The response was linear over the range 0.25-20 µM, and the detection limit was 0.1 µM. None of the cations investigated interfered. Interference caused by some organic compounds usually present in radiopharmaceutical preparations is reported.
Tin(II) Dental Amperometry Electrode Sample preparation Interferences Buffer Complexation

"Multichannel Electrochemical Analyses Of Enzyme Reactions"
Electroanalysis 1996 Volume 8, Issue 8-9 Pages 748-752
Nahoko Kasai, Tomokazu Matsue *, Isamu Uchida

Abstract: A multichannel microarray electrode was fabricated by the Au-sputtering technique. The array was mounted in a flow-through cell equipped with an Ag/AgCl reference electrode and a Pt-wire counter electrode. Enzyme-catalyzed reactions involving horseradish peroxidase or xanthine oxidase were investigated in continuous-flow systems involving 0.1 M phosphate buffer of pH 7.5 or 60 mM carbonate buffer of pH 10.7, respectively, as the mobile phase (1 ml/min). The acquired data were used for the determination of the Michaelis constant and the molecular activity.
Enzymes Electrode Immobilized enzyme Buffer Equilibrium constants

"Torulopsis Candida-based Sensor For The Estimation Of Biochemical Oxygen Demand And Its Evaluation"
Electroanalysis 1996 Volume 8, Issue 7 Pages 698-701
S. Sangeetha, G. Sugandhi, M. Murugesan, V. Murali Madhav, Sheela Berchmans, R. Rajasekar, Sumathi Rajasekar, D. Jeyakumar, G. Prabhakar Rao *

Abstract: The cited micro-organism was grown in a broth and harvested by centrifugation. The isolated microbes were dispersed in phosphate buffer of pH 7 and immobilized on a cellulose nitrate membrane by adsorption on to the pores, which was effected by filtration of a 0.5 mL portion of the dispersion through the membrane under reduced pressure. The prepared membrane was coupled to a dissolved O2 sensor by means of dialysis membrane kept in position with an O-ring. The sensor was used in a FIA system with phosphate buffer as the carrier stream (25 ml/h). Amperometric measurements were made at an applied potential of -0.6 V vs. Ag/AgCl. Calibration graphs were constructed with standard solutions of glucose/glutamic acid, and were linear up to 500 mg/l, corresponding to a BOD value of 370 ppm. The sensor, which is intended for application to effluents, exhibited good stability and a fast response time.
Oxygen, biochemical Waste Environmental Sensor Dialysis

"Miniaturized Reference Electrodes With Microporous Polymer Junctions"
Electroanalysis 1996 Volume 8, Issue 7 Pages 673-675
Jairo J. Pedrotti, L&uacute;cio Angnes, Ivano G. R. Gutz *

Abstract: The construction and evaluation of a simple and effective mini-reference electrode is presented. Major innovations are the use of high density microporous polyethylene for the restricted flow junction between the internal and external electrolyte and a polypropylene disposable pipette tip as the electrode body. Low electrolyte bleeding, reduced size, relatively low electrical resistance and simplified procedure of construction are some of the advantages of the presented design. These characteristics make this electrode particularly suitable for use with small-volume cells and flow cells, as well as applications where chloride contamination should be avoided. Other applications for the microporous membrane in electroanalysis are introduced.
Voltammetry Electrode

"Redox Polymers For Electrocatalytic Oxidation Of NADH-cationic Styrene And Ethylenimine Polymers"
Electroanalysis 1996 Volume 8, Issue 6 Pages 575-581
Zhengwei Huan, Bj&oacute;rn Persson *, Lo Gorton *, Suresh Sahni, Terje Skotheim, Philip Bartlett

Abstract: Solid electrodes were prepared by deposition of a redox polymer solution in DMSO onto the polished surface of a spectrographic graphite rod in a PTFE holder. The polymers investigated were a styrene polymer incorporating positive charges through quaternary amines and Toluidine Blue O (I) moieties and a branched polyethyleneimine with part of its primary amine groups loaded with I. Cyclic voltammograms were recorded for NADH in 0.25 M phosphate buffer of pH 7 with a SCE and Pt wire electrode as reference and counter electrodes, respectively. Rotating disc electrode experiments were conducted similarly at 100 rad/s. The catalytic efficiency of the electrodes was investigated. Carbon paste enzyme electrodes for D-glucose and L-malate were prepared from a mixture of 0.1 M phosphate buffer of pH 7, NAD+, glucose dehydrogenase or L-malic dehydrogenase, polyethyleneimine solution and graphite powder modified with the redox polymers. The mixture was dried and the residue was mixed with paraffin oil. The paste was packed into plastic syringes containing the unmodified carbon paste and a Ag wire for electrical contact. Sensor response was investigated in a FIA system using 0.25 M phosphate buffer of pH 7 as the carrier stream into which the analyte was injected. Calibration graphs were linear for 0.1-5 mM D-glucose with a detection limit of 50 µM.
Glucose Nicotinamide adenine dinucleotide reduced Voltammetry Redox

"Electrochemically Prepared And Optimized Membrane Compositions For Silver(I)-responsive Chalcogenide-based Ion-selective Electrodes"
Electroanalysis 1996 Volume 8, Issue 6 Pages 557-564
Milka T. Neshkova*, Elka M. Pancheva

Abstract: Different silver chalcogenide membranes of varying thicknesses were deposited on Pt cylindrical cathodes hermetically sealed in a glass tube. The electrolyte consisted of a constant Ag-to-Se molar ratio of 1:25 in 0.5 M H2SO4 with or without addition of TeO2 to give a Te-to-Se molar ratio varying from 1:15 to 1:5. The selectivity and response of the membranes to Ag+ ions were investigated under steady-state and flow injection conditions. A detection limit of 1.6 nM was obtained for the membrane Ag2+δSe1-xTex. The performance of this membrane was superior to that of commercially used Ag2S pressed-pellet membranes as regards selectivity and stability.
Silver Electrode

"Pulsed Amperometric Detection Of Ethanol In Breath By Gold Electrodes Supported On Ion Exchange Membranes (solid Polymer Electrolytes)"
Electroanalysis 1996 Volume 8, Issue 6 Pages 544-548
Gilberto Schiavon, Nicola Comisso, Rosanna Toniolo, Gino Bontempelli*

Abstract: A sensitive and fast-responding amperometric sensor for the determination of ethanol in breath which eliminates oxygen interferences is described. It consists of a porous gold working electrode (facing the sample) supported on one face of an ion-exchange membrane which serves as a solid polymer electrolyte (SPE). The other side of the membrane faces an internal electrolyte solution (1 M aqueous NaOH) containing the counter and reference electrodes. The fouling of the gold working electrode, due to the ethanol oxidation process, is overcome by continuously cleaning and reactivating its surface by applying a triple-pulse potential waveform. The performance of this sensor has been tested in a closed-loop flow apparatus fed with synthetic ethanol-vapor samples obtained by evaporating aqueous solutions with known ethanol contents. The sensor displays a high current sensitivity and a low background noise, so that a low detection limit (2 g L-1, 1ppm v./v.) is estimated for a signal-to-noise ratio of 3. The responses are characterized by both a good reproducibility and a linear dependence on the ethanol concentration over a fairly wide range (more than three orders of magnitude), as well as by a short response time (ca. 1 s). This fast response time arises from the lack of a gas-permeable membrane and direct gas contact to the triple interphase among the gaseous analyte, the porous working electrode and the solid polymer electrolyte. The absence of significant interfering effects and the possibility of adopting such a device for the detection of ethanol in fermentation processes are also discussed.

"Development Of An Amperometric Enzyme Biosensor For The Determination Of The Antioxidant T-butylhydroxyanisole In A Medium Of Reversed Micelles"
Electroanalysis 1996 Volume 8, Issue 6 Pages 529-533
M. Asuncion Ruiz, A. Julio Reviejo, Concepcion Parrado, Jose M. Pingarr&oacute;n

Abstract: A portion (5 g) of ground biscuit was extracted by shaking with 3 x 25 mL portions of ethyl acetate. After centrifugation, the combined extracts were concentrated to a small volume and diluted to 50 mL with a reversed micellar system consisting of ethyl acetate/0.1 M dioctyl sulfosuccinate/50 mM phosphate buffer of pH 7.4. A portion (150 µL) was injected into a flow injection system in which the carrier stream of the same micellar system. Amperometric measurements were made with a BAS VC-2 tyrosinase electrode, a Ag/AgCl electrode and a Pt wire electrode as the working, reference and counter electrodes, respectively. Calibration graphs were linear up to 1 mM t-butylhydroxyanisole with a detection limit of 30 µM. Batch experiments were also carried out in which the detection limit was 0.1 mM and the linear range was 0.2-2 mM. Of the common antioxidants usually used in food products, only propyl gallate interfered.
2-tert-Butyl-3-methoxyphenol Food Amperometry Sensor Electrode Electrode Micelle Interferences

"Amperometric Flow Injection Analysis Of Organic Thiols And Proteins"
Electroanalysis 1996 Volume 8, Issue 5 Pages 468-472
Achmad Hidayat, D. Brynn Hibbert *, Peter W. Alexander

Abstract: Portions (10 µL) of standard L-cysteine (I) solution was injected into a carrier stream of 100 mM phosphate buffer of pH 3.1 containing 15 µM-Hg(II) [1.5 ml/min] of a flow injection system and detected at a W electrode at -0.24 V vs. Ag/AgCl with a Pt wire auxiliary electrode. The calibration graph was linear over the range 0.25-100 µM-I with a detection limit of 0.25 µM. Silver and iodate ions were observed to interfere. Thiourea (II), glutathione (III), DNA and albumin were similarly detected, and appropriate analytical data are briefly presented. I, II, reduced-III, DL-homocysteine, DL-penicillamine and 3-mercaptopropanoic acid were resolved by HPLC on a Zorbax ODS column (25 cm x 4.6 mm i.d.), aqueous 50 mM 3-chloroacetate/methanol (99:1) of pH 2.3 as mobile phase (0.3 ml/min) and post-column reaction with 50 mM phosphate buffer of pH 2.3 containing 15 µM-Hg(II) (1 ml/min) for amperometric detection as before.
Cysteine Thiols Amperometry HPLC Interferences

"A Serial Array Of ISE For Use In A Portable Battery-powered Flow Injection Analyser"
Electroanalysis 1996 Volume 8, Issue 5 Pages 438-442
Telis Dimitrakopoulos, Peter W. Alexander *, D. Brynn Hibbert

Abstract: Natural water samples (200 µL) were injected into a carrier stream of either 50 mM MgSO4, 1 mM CaCl2 or 7 mM lithium acetate (6.8 ml/min) of a flow injection potentiometric system and the K, Na and nitrate ions were simultaneously detected using a planar ISE serial array (schematic shown; details given). Calibration data of the respective standard ion solutions treated with 1 mM CaCl2, and analytical data of the studied ions in the three carrier solutions are presented and discussed. The method was applied to the analysis of two natural mineral water samples (details given). Results were in good agreement with those obtained by the standard AAS method.
Nitrate Potassium Sodium Mineral Environmental Electrode Electrode Electrode Potentiometry Portable Method comparison

"Iridium-dispersed Carbon-paste Enzyme Electrodes"
Electroanalysis 1996 Volume 8, Issue 5 Pages 434-437
Joseph Wang *, Gustavo Rivas, Manuel Chicharro

Abstract: Enzyme electrodes were prepared by mixing 25 mg glucose (I) oxidase with 10 mg polyethylenimine and the mixture was added to 298 mg Ir-containing C paste (5% Ir-on-C/mineral oil [27:23]). The resultant paste was packed into the electrode cavity (3 mm diameter) of a PTFE electrode body and electrical contact was established via a stainless steel screw. Portions of standard solutions of I were analyzed under batch conditions at 0.0 V vs. Ag/AgCl in 50 mM phosphate buffer of pH 7.4 and containing 30 mM NaCl, using the Ir-enzyme electrode and a Pt wire counter electrode. The calibration graph was linear up to 5 mM I with an RSD (n = 10) of 2.1% at 4 mM I. Using FIA, a 20 µL injection and a carrier stream (1.5 ml/min) of 50 mM phosphate buffer of pH 7.4 and containing 30 mM NaCl, calibration graphs were approximately linear up to 20 mM I, with an RSD (n = 32) of 1.4% for 10 mM I.
Glucose Sensor Electrode

"Bienzyme Sensors Based On Poly(anilinomethylferrocene)-modified Electrodes"
Electroanalysis 1996 Volume 8, Issue 5 Pages 414-419
Ashok Mulchandani*, Chia-Lin Wang

Abstract: Amperometric bienzyme electrodes for glucose (I), lactic acid (II) and glutamic acid (III) were constructed using their corresponding oxidases immobilized on a horseradish peroxidase-poly(anilinomethylferrocene)-modified vitreous C electrode as described previously by Mulchandani et al., (Anal. Chem., 1995, 67, 94). After drying, resorcinol (RES) and o-phenylenediamine (POD) were polymerized onto the electrode surface by cycling the electrode between 0 and 0.65 V vs. Ag/AgCl in a solution containing 1.5 mM RES and 1.5 mM OPD and 100 mM NaClO4 in 100 mM phosphate buffer. The three analytes were determined in 100 mM NaClO4 at -50 mV, and by FIA using a 20 µL sample injection into a carrier stream of 100 mM citrate-phosphate buffer of pH 5.5-7 and containing 100 mM NaClO4 and 120 mM NaCl. Analytical performance data of the three enzyme electrodes are presented, and compared favourably with comparative colorimetric analyzes. No electrode interference was shown in the presence of up to 0.06 mM ascorbic acid, 0.33 mM uric acid or 2 mM acetaminophen.
Glucose 2-Oxoglutaric acid Lactic acid Sensor Amperometry Interferences

"A Photocured Calcium Ion-selective Electrode For Use In Flow Injection Potentiometry That Tolerates High Perchlorate Levels"
Electroanalysis 1996 Volume 8, Issue 4 Pages 391-395
Telis Dimitrakopoulos*, John R. Farrell, Peter J. Iles

Abstract: A poly(methylmethacrylate) [PMMA] wall-jet electrode flow cell (2 µL dead volume) accommodating a commercial PMMA ISE (12 mm diameter) with an embedded Cu disk (6 mm diameter) coated with a Ca selective photo-cured membrane (preparation described) based on the calcium bis[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate ionophore and a lipophilic additive, potassium tetrakis(p-chlorophenyl) borate. Carrier and reference streams of 0.1 M NaCl were pumped (1.5 ml/min) through the flow cell and over a Ag/AgCl reference electrode with potentiometric detection. A 100 µL sample was injected into the carrier stream manually. Calibration plots (E/mV) exhibited log-linearity for 0.01-10 mM Ca(II) in CaCl2, which was unchanged in a 0.01 M NaCl/0.01 M NaClO4 (9:1) or 0.1 M NaClO4. The detection limit was 1 µM-Ca(II). The photo-cured electrode was satisfactory for Ca(II) measurements in the presence of high perchlorate levels and was used to measure total Ca(II) in full-cream milk. Results were in good agreement with those obtained by AAS.
Calcium Milk Electrode Potentiometry Method comparison

"Preconcentration By Flow Reversal In Conductometric Sequential Injection Analysis Of Ammonium"
Electroanalysis 1996 Volume 8, Issue 4 Pages 387-390
M. T. Oms, A. Cerd&agrave;, Victor Cerd&agrave; *

Abstract: A 75 µL portion of standard ammonium ion (I) solution and 100 µL 0.05 M NaOH were aspirated into a holding coil (150 cm x 1.5 mm i.d.) and transferred to the base compartment of a diffusion cell (construction described). The NH4+ ions were separated from the upper compartment which contained 0.05 M H3BO3 with a gas permeable membrane (0.22 µm pore) and NH3, which diffused through the latter, was absorbed in the H3BO3 and transferred to a 20 µL flow-through conductivity cell (described) with additional H3BO3 held in a coil (150 cm x 1.5 mm i.d.). Calibration graphs (relative conductivity) were linear up to 120 and 180 mg/l of I, respectively, with 0.05 M and 0.1 M H3BO3, respectively. The detection limit of 1.5 mg/l with an RSD of 3%, was reduced to 0.1 mg/l with pre-concentration achieved by five successive sample flow reversals (discussed), but the linear range was reduced to 80 mg/l. The procedure was applied successfully to the analysis of ammonium ions in waste waters.
Ammonium Environmental Waste Conductometry Sequential injection Preconcentration

"Studies Of The Preparation And Analytical Application Of Polypyrrole-coated Microelectrodes For The Determination Of Aluminum"
Electroanalysis 1996 Volume 8, Issue 4 Pages 330-335
Joseph N. Barisci, Peta Murray, Chris J. Small, Gordon G. Wallace *

Abstract: A Pt disk (10 µM diameter) precoated with 1% Nafion in ethanol (preparation described) was immersed in 0.1-0.2 M pyrrole and 0.05 M sodium catechol-3,5-disulfonate and polypyrrole (PP) was deposited galvanically on the electrode with current densities of 0.2-2 mA/cm2 for 1-2 min. Potentials were measured vs. a Ag/AgCl (3 M NaCl) reference electrode and a Pt mesh auxiliary electrode. Microelectrodes prepared galvanically or potentiodynamically (procedures described), with other sulfonated aromatic counter ions (tabulated) or 8-hydroxyquinoline, were less satisfactory. FIA of Al(III) was performed in 1 mM Na2SO4 as a support electrolyte with a PP coated Pt disk working electrode, Ag/AgCl (3 M NaCl) reference electrode; a stainless steel cell-outlet fitting served as an auxiliary electrode. Detection with a pulse electrochemical detector. Calibration plots (potential pulse height) were linear up to 100 ppb Al(III) and the detection limit (2 x noise) was 20 ppb. The RSD was 6% for 40 ppb Al(III). The electrodes did not display complete selectivity (discussed) for Al(III) in the presence of Fe(III), Mn(II), Ca(II), Mg(II) or K(I).
Aluminum(III) Electrode Electrode 8-Hydroxyquinoline

"Cyclic Voltammetry With Harmonic Lock-in Detection: Applications To Flow Streams"
Electroanalysis 1996 Volume 8, Issue 4 Pages 314-319
John K. Cullison, Werner G. Kuhr *

Abstract: Cyclic voltammetry (CV) was used for FIA of 1 µM-hexammineruthenium(III) chloride (I) in 0.15 M KCl/50 mM phosphate buffer of pH 7.4 with a C disk (32 µm diameter) working electrode and a Ag/AgCl reference electrode. Each linear scan, at ~40 mV/s and repeated at 100 ms intervals, was swept cathodically from 0.01 V to -0.29 V. The detection limit was ~200 nM-I. Lock-in detection at the second harmonic (phase-angle +100°C) with FIA of 3.7 nM-I was performed with a fundamental modulation frequency of 25 Hz and the amplifier locked-in at /50 Hz. The lock-in signal was linear from ~5 nM (detection limit) over at least four orders of magnitude. The DC amperometric response for 250 nM-I was measured with the potential set to 200 mV more negative than the formal potential of the redox couple. The detection limit was 25 nM-I. CV of 1.3 mM ferrocene in 0.5 M tetrabutylammonium perchlorate in CH3CN was performed with a Au disk (10 µm diameter) working electrode and a potential window of -0.3 to 0.15 V vs Ag/AgCl. The scan rate, 180 V/s corresponded to a fundamental frequency of 200 Hz. Similar CV studies of 10 µM-glucose (II) in 0.1 M NaOH were made. Results are tabulated.
Voltammetry Electrode

"Effect Of Membrane Composition On The Flow Injection Response Of An Ion-selective Electrode: A Comparative Study Based An Selectivity Coefficients Calculated Using A Data Linearization Technique"
Electroanalysis 1996 Volume 8, Issue 3 Pages 274-279
David E. Davey, Dennis E. Mulcahy, Gregory R. O'Connell*

Abstract: Portions of 100 µL of iodide solutions containing 100 mM bromide, thiocyanate and thiosulfate as interferents were injected into carrier and reagent streams (total flow 6.6 ml/min) of 1 µM-KI and 100 mM KNO3, and iodide detected using a variety of purpose made AgI/Ag2S (details given) and commercially available iodide, sulfide and cadmium ISE. Calibration graphs of the respective ISE responses are presented. Most sensors showed good analytical performance, excepting that prepared from a 3:1 AgI/Ag2S membrane.
Iodide Electrode Electrode Electrode Potentiometry Interferences

"Detection Of Cytochrome C Using A Conducting-polymer Mediator-containing Electrode"
Electroanalysis 1996 Volume 8, Issue 3 Pages 248-252
Wen Lu, Huijun Zhao, Gordon G. Wallace *

Abstract: A 0.018 cm2 Pt-disc electrode was immersed into phosphate buffer of pH 6.8 containing 200 mM pyrrole and as a mediator 100 mM ferricyanide ion (I), and a polypyrrole-I layer formed using a current density of 3 mA/cm2 at 850 mV vs. Ag/AgCl. Portions (20 µL) of cytochrome c (II) were injected into a carrier stream (1 ml/min) of 100 mM phosphate buffer of pH 10, and II was detected at 200 mV. Calibration graphs were non-linear up to 25 µM-II with a detection limit of 0.1 µM.
Cytochrome C Amperometry Electrode

"Electocatalysis And Measurements Of Hydrazine Compounds At Glassy-carbon Electrodes Coated With Electropolymerized 3,4-dihydroxybenzaldehyde Films"
Electroanalysis 1996 Volume 8, Issue 3 Pages 244-247
Prasad V. A. Pamidi, Joseph Wang *

Abstract: Vitreous and screen-printed C electrodes were immersed in 50 mM phosphate buffer of pH 7.5 solution containing 1 mM 3,4-dihydroxybenzaldehyde (I), and I polymerized on to the electrode surface by potential cycling five times between -200 to +300 mV at 50 mV/s. Portions of 20 µL of aqueous hydrazine (II) and 1,2-dimethylhydrazine (III) were injected into carrier streams (1 ml/min) of 50 mM phosphate buffer of pH 7.5 and detected at 400 mV vs. Ag/AgCl and a Pt-wire counter electrode. Calibration graphs were linear from 0.2-1.2 µM-II and III with a detection limit of 0.2 µM-II. At 1 mM II RSD (n = 15) of 4.7% was obtained. An application of the technique to the use of thick-film sensors is briefly described.
Hydrazine Amperometry Catalysis

"Flow Injection Amperometric Detection Of Ammonia Using A Polypyrrole-modified Electrode And Its Application In Urea And Creatinine Biosensors"
Electroanalysis 1996 Volume 8, Issue 3 Pages 233-243
Marek Trojanowicz *, Andrzej Lewenstam, Tadeusz Krawczyski Vel Krawczyk, Ilkka L&auml;hdesm&auml;ki, Wojciech Szczepek

Abstract: Pt disc electrodes were immersed in a solution of 100 mM pyrrole in 100 mM NaCl, and polypyrrole formed on the surface over a period of 3 min at 800 mV vs. Ag/AgCl. Using the electrodes in 100 mM NaCl, calibration graphs were linear up to 100 µM-NH4Cl, and an RSD of 0.9-2% at 100 µM-NH4Cl. A mechanism of response of ammonia with the sensor is discussed. Enzyme immobilized sensors were prepared by adding a 5 µL of aqueous 1.5% glutaraldehyde to a suspension of either 0.5-2 mg urease or 1 mg creatinine (I) iminohydrolase in 15 µL water. After mixing, the mixture was spotted on to a wetted Cuprophan membrane, mounted on to the electrode and dried at 4°C for 3-4 h. Serum was diluted tenfold with water and 100 µL injected into a carrier stream (500 µL/min) of water, and merged with a stream (500 µL/min) of 50 mM borate buffer of pH 9.2 containing 140 mM NaCl. Urea was determined using a 1.6 mm diameter Pt electrode at 300 mV vs. Ag/AgCl. Calibration graphs were linear up to 3 mM urea, with an RSD (n = 24) of 0.8%. I was determined similarly using a I-iminohydrolase immobilized sensor, with a calibration graph linear up to 2 mM I and a detection limit of 0.1 mM I.
Ammonia Creatinine Urea Blood Serum Amperometry Sensor Electrode

"Electro-oxidation Of Ascorbic Acid On The Dispersed-platinum Glassy-carbon Electrode And Its Amperometric Determination In Flow Injection Analysis"
Electroanalysis 1996 Volume 8, Issue 2 Pages 128-134
Innocenzo G. Casella *

Abstract: The electrode was prepared by depositing a solution (10 µL) of 30 mM PtCl4 onto the surface of a polished vitreous C electrode. The electrode was dried at 40°C for 30 min and conditioned for 1 h in 50 mM HClO4 using cyclic voltammetry between -0.3 and 1.3 V vs. SCE; a Pt foil electrode was used as counter electrode. Voltammograms were again recorded after addition of 20 mM ascorbic acid (I) in the supporting electrolyte. Response was linear up to 100 mM I. The effects of scan rate and pH of the supporting electrolyte were investigated and reported. The sensor was used in a FIA system using an applied potential of 0.6 V. The effects of flow-rate of the carrier solution and presence of foreign species were reported. Results obtained for samples of fruit juices were in good agreement with those obtained by HPLC methods. Recoveries were >99%.
Ascorbic acid Fruit Amperometry Electrode Voltammetry

"Development And Optimization Of A Solid Composite Tyrosinase Biosensor For Phenol Detection In Flow Injection Systems"
Electroanalysis 1996 Volume 8, Issue 2 Pages 117-123
E. S. Mareikelutz, Elena Dominguez *

Abstract: The biosensor was constructed by preparing a mixture of graphite-epoxy resin (50 mg), accelerator (50 mg) and tyrosinase (1 mg) and inserting the mixture into the tip of a polypropylene syringe, which already contained unmodified graphite/paraffin oil paste. An Ag wire was used for electrical contact. The mixture was allowed to harden for 48 h and the electrode was polished prior to use. Amperometric measurements were made by applying a potential of -100 mV vs. Ag/AgCl reference electrode; a Pt-wire electrode was used as counter electrode. The biosensor was used in an FIA system using 0.1 M phosphate buffer of pH 6 as the carrier solution. The effects of modifying the composition of the electrode mixture by: (i) addition of phosphate buffer solution of different pH; (ii) addition of inorganic substances; and (iii) addition of Ru, Au and Pd powder, were investigated and reported. Optimum response and peak resolution were obtained with a mixture of the resin with the enzyme in the dry state and Au/Pd powder.
Phenol Sensor Amperometry Optimization

"A Portable Flow Injection Analyzer For Use With Ion-selective Electrodes"
Electroanalysis 1995 Volume 7, Issue 12 Pages 1118-1120
Telis Dimitrakopoulos, Peter W. Alexander*, D. Brynn Hibbert, Len Cherkson, John Morgan

Abstract: A battery powered portable monitor based on flow injection potentiometry has been developed weighing 1.8 kg, constructed in a carry-case and applicable for remote site monitoring. Portability has been achieved using a light weight rechargeable Ni-Cd battery-pack (7.2 V). The flow injection manifold incorporates a low powered peristaltic pump, a wall-jet type flow cell containing a commercial iodide ion-selective electrode and a Ag/AgCl reference electrode connected to an analog-to-digital converter, also powered by the battery pack, and a RS232-serial output to a notebook computer for real-time data display and storage. The system performance has been evaluated using the iodide ion-selective electrode, including the effects of various carrier solutions on sample peak heights, peak widths and the calibration slopes and working ranges. Fast response with peak widths as low as approximately 10 s. was observed with near Nernstian response of -53.8 mV change per activity decade and a log-linear range between 5 x 10^-6 and 1 x 10^-2 M in a 0.1 M sodium acetate carrier stream.

"Online Amperometric Assay Of Glucose, L-glutamate, And Acetylcholine Using Microdialysis Probes And Immobilized Enzyme Reactors"
Electroanalysis 1995 Volume 7, Issue 12 Pages 1114-1117
Toshio Yao, Seita Suzuki, Hirohito Nishino, Taketoshi Nakahara

Abstract: A highly selective online, real-time monitoring system is proposed for amperometric assay of glucose, L-glutamate, and acetylcholine. The system includes a microdialysis probe, immobilized enzyme reactor, and poly(1,2-diaminobenzene)-coated platinum electrode. The analyte in the dialysate from the microdialysis probe is enzymatically converted to produce hydrogen peroxide. The hydrogen peroxide is detected selectively at a poly(1,2-diaminobenzene)-coated platinum electrode, without any interference from oxidizable species and proteins. The present method can be successfully applied to in vitro assay of glucose and in vivo monitoring of glucose in rat brains. However, the sensitivity is not sufficient for in vivo monitoring of trace amounts of L-glutamate and acetylcholine in rat brains. (11 references)
Acetylcholine Glucose l-Glutamate Brain Amperometry Electrode Electrode Immobilized enzyme Sensitivity Interferences Dialysis

"Bilayer Lipid Membranes As Electrochemical Detectors For Flow Injection Immunoanalysis"
Electroanalysis 1995 Volume 7, Issue 11 Pages 1082-1089
Dimitrios P. Nikolelis, Christina G. Siontorou, Vangelis G. Andreou, Kyriakos G. Viras, Ulrich J. Krull

Abstract: This work describes the use of filter-supported stabilized bilayer lipid membranes (BLMs) for the rapid electrochemical monitoring of an immunological reaction in flowing solution streams. BLMs were prepared from egg phosphatidylcholine (egg PC) and dipalmitoyl phosphatidic acid (DPPA) and the ultrafiltration membranes used were composed of glass microfibers. Thyroxin (T4)/anti-rabbit T4 was used as a representative immunological reaction for these studies. Antibody was incorporated into a floating lipid matrix at an air-electrolyte interface, and then a casting procedure was used to deliver the lipid onto the filter supports for BLM formation. Injections of antigen were made into flowing streams of a carrier electrolyte solution. Experiments were done in a stopped-flow mode using lipid mixtures containing 15% (w/w) DPPA to provide only a single transient current signal with a magnitude related to the antigen concentration. Differential scanning calorimetric experiments provided evidence that the antibody-lipid interactions at the BLMs occurred through electrostatic interactions. BLMs containing 35% DPPA were used to examine regeneration of the active sites of antibody after complex formation by washing with the carrier electrolyte solution. Repetitive cycles of injection of antigen followed by regeneration of antibody binding activity have shown that the maximum number of cycles is about 5, followed by a degradation of signal for a larger number of injections. However, the sensor can also be easily regenerated by recasting of the existing lipid/antibody film at the air-electrolyte interface to form fresh BLMs.

"Ferrocene-containing Polymers As Electron Transfer Mediators In Carbon Paste Electrodes Modified With PQQ-dependent Aldose Dehydrogenase"
Electroanalysis 1995 Volume 7, Issue 10 Pages 941-946
Maria Smolander, Lo Gorton, Hung Sui Lee, Terje Skotheim, Hsing-Lin Lan

Abstract: Four different polymer-bound ferrocene derivatives were evaluated as electron transfer mediators in aldose biosensors based on aldose dehydrogenase with pyrroloquinoline quinone (PQQ) as co-enzyme. The polymeric ferrocene derivatives (syntheses described) were mixed with C paste and packed into a plastic syringe holder that had been pre-packed with unmodified C paste. A solution of aldose dehydrogenase in 10 mM sodium acetate of pH 5 containing 0.1% Triton X-100 was applied to the electrode surface and allowed to dry. The electrodes were evaluated in a flow injection system equipped with a wall-jet amperometric cell using 50 mM sodium phosphate buffer of pH 6.5 as carrier (0.7 ml/min). Maximum response was obtained at +300 mV vs. Ag/AgCl but measurements were normally made at +200 mV to minimize interference from non-specific oxidation processes. The electrodes were more stable than those modified with monomeric dimethylferrocene. The best response was obtained with polymethyl(11-ferrocenyl-4,7,10-trioxa-undecanyl)methyl (12-amino-4,7,10-tioxa-dodecyl)siloxane (1:1) and electrodes prepared from this derivative was applied to the determination of xylose in fermentation mixtures; the results agreed with those obtained by LC.
Aldoses Xylose Fermentation broth Sensor Electrode Electrode Amperometry Electrode Interferences Method comparison Triton X Surfactant

"Flow Injection Liposome Immunoanalysis (FILIA) With Electrochemical Detection"
Electroanalysis 1995 Volume 7, Issue 9 Pages 838-845
Alison J. Edwards *, Richard A. Durst

Abstract: Alachlor (I) in environmental samples was covalently bonded to dipalmitoyl phosphatidylethnolamine using N-succinimidyl-S-acetylthioacetate as described by Siebert et al. (Anal. Chim. Acta 1993, 282, 297). The I-bonded lipid was then dissolved in an organic solvent (not specified) and reacted with aqueous 100 mM potassium ferrocyanide of pH 7.4. After sonication and removal of the organic solvent, the liposome suspension was reacted with further potassium ferrocyanide (no details given) at 45°C, filtered, gel-filtered and dialysed. The dialysed liposomes were then diluted in PBS of pH 7.4 and 20 µL injected onto a column (5 cm x 4.3 mm i.d.) containing I-antibody-immobilized glass beads (preparation details given), PBS as mobile phase (0.55 ml/min) and amperometric detection at +330 mV vs. Ag/AgCl. Calibration graphs were linear for 1-10% liposomes bound on-column, with a detection limit of 0.5 ng I on-column.
Alachlor Environmental Amperometry Glass beads Immobilized antibody Liposomes

"Investigation Of Batch Measurements With Immobilized Enzyme Reactors And Amperometric Electrodes"
Electroanalysis 1995 Volume 7, Issue 8 Pages 785-787
Aziz Amine, Giuseppe Palleschi

Abstract: The optimization of all parameters which govern the response of a biosensor is generally very difficult. Flow-injection analysis with an immobilized enzyme reactor (IER) is considered as a complementary method or possibly an alternative to a biosensor. Similarly, the proposed batch experiments with an IER, can in many instances advantageously replace the biosensor. The principle consists of successive insertions of appropriate IERs into the cell solution after a steady-state current output has been recorded from the interfering species present in the solution. Selected examples of enzymatic assays in food samples, aimed either at eliminating electrochemical interferences or allowing multi-substrate determinations are reported and discussed.
Food Amperometry Interferences Immobilized enzyme

"A Tubular Graphite-epoxy Electrode Incorporating Horseradish Peroxidase As A Potentiometric Sensor For Hydrogen Peroxide"
Electroanalysis 1995 Volume 7, Issue 8 Pages 722-725
Zulfikar, D. Brynn Hibbert*, Peter W. Alexander

Abstract: A novel potentiometric peroxidase enzyme sensor based on a tubular graphite-epoxy design is reported for the determination of hydrogen peroxide in an FIA system. The sensor was formed from horseradish peroxidase (40 mg), graphite (240 mg) and epoxy (780 mg). Hydrogen peroxide, injected into pH 7,0.05 M phosphate buffer at 26°C, was determined with a linear slope of 45.6 mV/decade in the concentration range 7.5 x 10^-7 to 5.0 x 10^-5 M. Acceptable reproducibility of 1.2% relative standard deviation was obtained in the flow injection analysis. The advantages of this sensor are low cost, simple electronic circuit design and better selectivity than amperometric sensors and a detection limit comparable with other methods.

"Flow Injection Potentiometric Determination Of Harmine And Harmaline Hallucinogens"
Electroanalysis 1995 Volume 7, Issue 7 Pages 656-659
Saad S. M. Hassan, Eman M. Elnemma, Marawan A. Hamada

Abstract: The sensor consisted of a polished Ag disc (0.9 cm o.d.) which was fixed to a small piece of polyethylene tubing (0.5 cm long, 1 cm o.d.) which was in turn fixed to the inner surface of a glass tube (7 cm long, 1 cm i.d.). The inner surface of the disc was soldered with Ag epoxy to the Cu core of a coaxial cable. A mixture consisting of 10 mg harmine or harmaline tetraphenylborate or reineckate, 352 mg dioctylphthalate or tributylphosphate, 187 mg PVC powder and 7 mL THF was prepared and packed into the sensor body. The solvent was allowed to evaporate to form a coating. The sensor was used in a FIA system using 0.1 M phosphate buffer of pH 4.6 as the carrier solution (5 ml/min). Potentiometric measurements were made relative to Ag/AgCl reference electrode. The response was linear from range 10 µM to 10 mM with a detection limit of 2 µg/ml. The effects of pH and the presence of foreign compounds were investigated.
Harmaline Harmine Potentiometry Electrode Electrode Interferences

"Electrocatalytic Amperometric Detection Of Hydroxylamine With A Palladium-modified Carbon Paste Electrode"
Electroanalysis 1995 Volume 7, Issue 6 Pages 556-559
Xiaohua Cai, Kurt Kalcher, Josef Lintschinger, Christian G. Neuhold, Janusz Tykarski, Bozidar Ogorevc

Abstract: Carbon paste electrodes (CPEs), modified by addition of Pd powder to the paste and electroactivation, exhibited electrocatalytic activity towards hydroxylamine. Electrogenerated palladium(0) at the electrode surface was found to be involved in the electrocatalytic oxidation of NH2OH. The electrode was employed as an amperometric detector for flow injection systems. Repeated injections (60) of hydroxylamine (5 ng) showed a relative standard deviation of 4.0%. Linear relation between the current and the analyte concentration was found between 0.1 and 10 ng of hydroxylamine. The detection limit was 20 pg NH2OH (3). The applicability of the method to the determination of hydroxylamine in river water was investigated.
Hydroxylamine River Amperometry Electrode Catalysis

"Amperometric Flow Injection Determination Of Citric Acid In Food Using Free Citrate Lyase And Co-immobilized Oxalacetate Decaboxylase And Pyruvate Oxidase"
Electroanalysis 1995 Volume 7, Issue 6 Pages 527-530
Kiyoshi Matsumoto, Tadayuki Tsukatani, Yuko Okajima

Abstract: Controlled-pore glass was refluxed with 6 M HCl for 6 h, dried and silanized with 10% (3-aminopropyl)triethoxysilane solution in toluene at 130°C for 10 h. Oxalacetate decarboxylase and pyruvate oxidase were co-immobilized (Matsumoto et al., Anal. Chem., 1988, 60, 147). This support was packed in to a glass tube (10 cm x 2 mm i.d.) and used in a FIA system with a carrier solution of 0.1 M phosphate buffer of pH 7 containing 10 mM MgCl2/80 µM-thiamine pyrophosphate/ 10 µM-flavine adenine dinucleotide. The sample (50 µL) and citrate lyase solution in phosphate buffer of pH 7 (80 µL) were injected in to the carrier stream (0.85 ml/min) and the mixture was pumped through a reactor containing ascorbate oxidase immobilized on controlled-pore glass to remove L-ascorbate, and then through the prepared reactor. H2O2 was determined amperometrically in a flow-through cell equipped with a Pt working electrode set at +0.6 V vs Ag/AgCl. Calibration graphs were linear from 0.1-1 mM citrate. The detection limit was 0.02 mM; RSD was 1.23% at the 0.5 mMlevel (n=10). An interference study was carried out (details given). The frequency was 15 tests/h. The system was applied to determination of citrate in several fruits; results correlated well with those from a kit enzymatic method.
Citric acid Fruit Amperometry Electrode Immobilized enzyme Interferences Controlled pore glass

"Ion-sensitive Field-effect Transistors And Ion-selective Electrodes As Sensors In Dynamic Systems"
Electroanalysis 1995 Volume 7, Issue 6 Pages 505-519
Andr&eacute;s Izquierdo, Mar&iacute;a D. Luque de Castro

Abstract: The use of the ion-selective sensors in continuous-flow systems is reviewed. Specific examples for selected analytes are given. Typical arrangements for different systems are described and performance comparisons are made. (145 references).
Field effect transistor Electrode Sensor Method comparison Review

"A Flow Injection/XPS Investigation Of The Effect Of Redox Equilibria On The Selectivity Of An Iodide-selective Electrode"
Electroanalysis 1995 Volume 7, Issue 5 Pages 461-470
David E. Davey, Dennis E. Mulcahy, Gregory R. O'Connell, Roger StC. Smart

Abstract: Bromide, thiocyanate and thiosulfate were studied as three moderately-interfering species. The flow injection (FI) manifold was as described earlier (Pure Appl. Chem, 1976, 48, 129). Potentiometric measurements were made with an Orion Research Model 710A digital pH/mV meter and the Orion 94-06A iodide ISE was used for most of the FI work. Neutral and acidified iodate and bromate oxidant streams increased the selectivity of the iodide electrode towards the interferents. Use of ascorbic acid or metabisulfite reducing streams resulted in a greater degree of selectivity towards iodide than was obtained with either of the neutral oxidant streams but a lower degree of selectivity than was obtained when a simple nitrate reagent stream was present. Thiosulfate damaged the surface of the electrode irreparably, with a concomitant excessive peak broadening in the FI experiment and very poor baseline recovery.
Iodide Electrode Potentiometry Interferences Redox Selectivity

"The Application Of Various Immobilized Crown Ether Platinum-modified Electrodes As Potentiometric And Amperometric Detectors For Flow Injection Analyses Of Catechol And Catecholamines"
Electroanalysis 1995 Volume 7, Issue 5 Pages 420-424
Suzanne K. Lunstord, Yi-Long Ma, Ahmed Galal, Cynthia Striley, Hans Zimmer, Harry B. Mark Jr.

Abstract: The crown ethers were polymerized onto a 2 mm diameter Pt disc electrode. The monomer solution comprised 0.025 M crown ether and 0.20 M tetrabutylammoniumtetrafluoriborate as supporting electrolyte in acetonitrile. Amperometric measurements were performed with a BAS model MF-1021 flow cell. Static potentiometric and potentiometric FIA measurements were performed with the polymer-modified electrode PTFE block incorporated into a standard BAS thin-layer flow cell with a Ag/AgCl electrode as second electrode. Measurements were performed with an Orion model 601A ionanalyzer. The potentiometric FIA response of all the crown ethers was linear over the range 10 mM to 10 µM. The lowest detection limits were 0.5 µmM for the potentiometric FIA with minimum interference from ascorbic acid, uric acid and acetaminophen. Detection limits for amperometric FIA was 5 µmM but there was significant interference from ascorbic acid, uric acid and acetaminophen.
Catechol, derivatives Catecholamine, derivatives Amperometry Electrode Electrode Potentiometry Crown ether Complexation Interferences

"Highly Sensitive Detection Of L-lactate And Pyruvate By Amperometric Flow Injection Analysis Based On Enzymatic Substrate Recycling And Selective Detection Of Hydrogen Peroxide"
Electroanalysis 1995 Volume 7, Issue 4 Pages 395-397
Toshio Yao, Masahiro Satomura, Tuketoshi Nakahara

Abstract: A poly(1,2-diaminobenzene)-coated Pt electrode (3 mm diameter) was used as an amperometric detector in a flow injection system incorporating a lactate-dehydrogenase/lactate oxidase coimmobilized reactor (27 x 3 mm i.d.) prepared as described previously (Ibid. 1991, 3, 493). The construction of the electrode is described. L-Lactate and pyruvate solutions (10 µL) were injected into a stream (0.4 ml/min) of 0.1 M phosphate buffer of pH 7.1 containing 0.2 mM NADH and carried to the reactor where H2O2 was generated. The detector was operated at 0.6 V vs. Ag/AgCl. The polymer film prevented NADH in the carrier stream from reaching the electrode surface. Only the generated H2O2 was detected. The sensitivity of the L-lactate and pyruvate determinations was enhanced 400-fold compared to the unamplified responses. The calibration graphs were linear for 20 nM- to 10 µM-pyruvate or L-lactate and the detection limit was 2 nM. The RSD were 0.81-1.8%.
l-Lactate Pyruvate Amperometry Electrode Immobilized enzyme Reactor Indirect

"Determination Of Penicillin By Triangle Programmed Coulometric Acid-base Flow Titration In A System Incorporating An Enzyme Reactor"
Electroanalysis 1995 Volume 7, Issue 4 Pages 356-361
Zs&oacute;fia Feh&eacute;r, T. Len Nguyen, G&eacute;za Nagy

Abstract: A flow-through coulometric titration technique is described which can be applied for the determination of a wide variety of compounds. If necessary, the sample can be transformed in the measuring system into a form which can be titrated. Thus an enzyme-catalyzed reaction can also be used as a sample pretreatment step. In this article a measurement technique and apparatus are described in which an enzyme-catalyzed reaction is used for the fast and reliable determination of penicillin compounds. The principle of the technique is that an enzyme reactor is built into the sample line of the measurement system used for performing coulometric triangle programmed titrations. One of the components of the reaction mixture leaving the reactor (in this case penicilloic acid) is determined by coulometric acid-base titration. This technique is especially useful for the analysis of large sample series.
Benzylpenicillin Coulometry Immobilized enzyme Titrations

"The Effect Of The Nature Of The Polymer Backbone On The Stability And The Analytical Response Of Polymer-modified Electrodes"
Electroanalysis 1995 Volume 7, Issue 4 Pages 333-339
A. P. Doherty, M. A. Stanley, G. Arana, C. E. Koning, R. H. G. Brinkhuis, J. G. Vos

Abstract: The synthesis, characterization and applications of the redox polymer [Os (bipy)2 (PS)7.5 (DMAP)2.5 Cl]Cl where bipy = 2,2'-bipyridyl, PS = polystyrene and DMAP = poly[4-(N-methyl-N-p-vinylbenzylamino)pyridine] are described. The polymer was characterized by spectrophotometry, luminescence, cyclic voltammetry and chronoamperometry. Modified electrodes were prepared by droplet evaporation of a 1% solution of the polymer on to 3 mm vitreous C electrodes. Electrochemical measurements were performed using SCE reference and Pt counter electrodes. The modified electrodes were applicable to the determination of Fe; the polymer mediated the reduction of Fe(III). The kinetic behavior was similar at rotating disc electrodes and in thin-layer flow cells. Fe was determined in pharmaceuticals by FIA using the modified electrodes as detectors. The carrier electrolyte was 0.1 M H2SO4 (1 ml/min) and the applied potential was -0.05 V vs. SCE. The calibration graph was linear for 10^-1000 µM-Fe(III) and the detection limit was 3 µM. The results agreed well with those obtained by spectrophotometry. The polymer was stable for 7 days.
Iron Pharmaceutical Electrode Electrode Electrode Method comparison

"Amperometric Batch Injection Analysis: Theoretical Aspects Of Current Transients And Comparison With Wall-jet Electrodes In Continuous-flow"
Electroanalysis 1995 Volume 7, Issue 3 Pages 225-229
Christopher M. A. Brett, Ana Maria Oliveira Brett, Lucian Costel Mitoseriu

Abstract: Amperometric detection using the batch injection analysis technique has been studied and compared with the current obtained at the wall-jet electrode under similar conditions using the oxidation of potassium ferrocyanide and the injection of samples of volume 10 to 100 µL. The form of the current transients has been analyzed and compared with the steady-state response at wall-jet disk electrodes. Good agreement is found at high dispension rate, differences at lower dispension rates being ascribed to radial diffusion effects. The importance of tip-electrode distance and injection volume have been evaluated; it is shown that the optimum distance is 3 mm and that maximum sensitivity requires a minimum injection volume of 14 µL. A detection limit of 50 µM using simple amperometric detection is estimated. Implications of these results for the efficient application of amperometric batch injection analysis are discussed.
Amperometry Electrode Theory

"An Extrapolation Method For The Fast Evaluation Of The Fluoride Ion-selective Electrode Equilibrium Potential In Continuous-flow Analysis"
Electroanalysis 1995 Volume 7, Issue 3 Pages 221-224
Xue D. Wang, Wei Shen, Robert W. Cattrall, Graeme L. Nyberg, John Liesegang

Abstract: The fluoride ion-selective electrode has been used in continuous flow analysis to determine the fluoride concentration in aqueous solution. The varying electrode potentials, E(t), were collected in the first 60 s by an interfacing computer, and the equilibrium potential of the electrode was predicted using an extrapolation method. This value agrees to within ±0.5 mV of the comparative value obtained by allowing sufficient time for the electrode to reach a steady state. Like flow-injection (FI), continuous flow (CF) analysis with this extrapolation method significantly shortens the time required for routine fluoride concentration measurements, but it also achieves a higher sensitivity than FI. The method has been applied to the determination of fluoride in city tap water.
Fluoride Water Electrode Extrapolation method

"Simultaneous Assays Of Glucose, Urate And Cholesterol In Blood Serum By Amperometric Flow Injection Analysis"
Electroanalysis 1995 Volume 7, Issue 2 Pages 143-146
T. Yao, M. Satomura, T. Nakahara

Abstract: The flow system featured a 16-way switching valve and a parallel configuration of three immobilized enzyme reactors. The enzymes; namely glucose oxidase, uricase and cholesterol oxidase were immobilized on controlled-pore glass packed into glass columns (1.8 cm x 3 mm i.d). Nafion film-coated and Nafion/cellulose acetate-coated Pt electrodes were used to selectively detect the H2O2 generated without any interference from electroactive species like L-ascorbate and proteins present in serum. The FIA system was similar to one described earlier (J. Biotechnol., 190, 14, 115). Serum was injected into two carrier streams of 0.1 M phosphate buffer of pH 7.5 and a stream of 0.1 M phosphate buffer of pH 7.5 containing 0.75% Triton X-100 (1 ml/min) which then passed through the enzyme reactors to the electrode detectors. The electrochemical flow cell had an Ag/AgCl reference electrode and a stainless steel tube as auxiliary electrode. Signal current was linear for 5-700 mg/dl glucose, 1-80 mg/dl uric acid and 5-100 mg/dl cholesterol. The RSD was better than 2.8% for the simultaneous assay of the three species in human control serum. Up to 32 samples per hour could be assayed.
Cholesterol Glucose Uric acid Blood Serum Amperometry Electrode Electrode Surfactant Interferences Controlled pore glass Immobilized enzyme Triton X

"Cation Determination In Aqueous Solution Using The Methyl Viologen-doped Zeolite-modified Carbon Paste Electrode"
Electroanalysis 1995 Volume 7, Issue 2 Pages 120-128
A. Walcarius, L. Lumberts*, E. G. Derouane

Abstract: Methyl viologen (MV2+) initially exchanged in a zeolite Y modified carbon paste electrode (ZMCPE) is reduced after being exchanged for the supporting electrolyte cation. The use of an electrolyte cation that cannot enter zeolite channels to a great extent does not give rise to appreciable currents while a non-size-excluded cation allows liberating MV2+ from zeolite particles and their subsequent reduction at the electrode-solution interface. Following those observations, the MV2+-based ZMCPE has been used for the constant potential (-0.85 V) amperometric detection of nonreducible:, non-size-excluded cations in aqueous medium. The performance of this electrode was investigated in both batch injection analysis (BIA) and flow injection analysis (FIA). The great advantage of BIA coupled to the amperometric detection is the ability to use electrolyte-free sample solutions. For FIA experiments, dissolved oxygen was eliminated by using an electrochemical scrubber containing porous carbon electrodes. With the MV2+-doped ZMCPE, alkali and alkali-metal cations can be detected at the submillimolar level for both batch and flow injection analysis.

"Characterization Of A Wall-jet Electrode/flow-injection Analysis System"
Electroanalysis 1994 Volume 6, Issue 11-12 Pages 1077-1082
Yu Liang Huang, Soo Beng Khoo, Miranda G. S. Yap*

Abstract: A wall-jet electrode (WJE) was studied as an electrochemical detector for flow-injection analysis (FIA). Mathematical expressions were obtained for the peak current responses of the electrode, both for an uncoiled open tubular conduit and also in the presence of a packed-bed reactor between the injection valve and detector. The derived relationships between peak current and volumetric flow rate, and injected sample volume and concentration of the analyte were verified by using the ferricyanide ion and hydrogen peroxide as test samples. In general, theory and experiment were in good agreement although a discrepancy in the volumetric flow rate dependence of the peak current was observed in the presence of a packed-bed reactor.

"Determination Of Aluminum Ions By Indirect Potentiometry In A Flow System"
Electroanalysis 1994 Volume 6, Issue 11-12 Pages 990-995
J. Catherine Ngila, Peter W. Alexander*, D. Brynn Hibbert

Abstract: A potentiometric system is described for the indirect flow determination of Al3+ with an aluminum wire as indicator electrode. The method is based on the reaction between aluminum and fluoride ions at pH 5.0 in acetate buffer. The reduction in activity of fluoride ions is detected by the aluminum electrode. The response was optimized for the flow rate of solution, length of reaction tubing, concentration of fluoride reagent, and pH of the buffer. The response was linear with concentration of aluminum in the range of 0.5 to 50 ppm with a relative standard deviation (RSD) of 0.7%. There was negligible interference from a range of cations and anions when their concentrations were less than 20 ppm.

"Polishable Composite Electrode Based Upon Graphite Powder Modified With An Electrochemically Deposited Catalyst"
Electroanalysis 1994 Volume 6, Issue 11-12 Pages 976-981
James A Cox*, Krzysztof Lewinski

Abstract: A polishable bulk-modified electrode is described that contains polymeric-mixed valent ruthenium oxide with cyano cross-links (mvRuCN) as a catalyst. Because mvRuCN is not available as an isolated compound, it was electropolymerized on graphite powder that was subsequently formed into a conducting composite with epoxy. Except for promoting oxidations at a more positive potential, this composite behaved the same as mvRuCN films on glassy carbon. Electrocatalytic oxidation of various N-nitrosamines, As(III), glutathione, isotocin, and myoglobin was observed. Flow-injection analysis of 50 M N-nitrosodi-n-propylamine with amperometric detection at the bulk-modified composite electrode yielded currents of 2.5 ± 0.1 A (5 trials) when the carrier solution is pH 1.5 phosphate buffer. The use of a micellar carrier,pH 1.5 phosphate buffer in 0.01 M hexadecyltrimethylammonium chloride, decreased the sensitivity of the flow-injection amperometric determination of N-nitrosodi-n-phenylamine by 50%, but otherwise, the behavior of the electrode was unchanged. The major advantages of the bulk-modified electrode over the surface-modified electrode jras the long-term stability (at least several months with dry storage) and polishability. Regarding trie latter, 19 replicates of the oxidation of As(III) yielded a relative standard deviation (RSD) of the current response of 3% when the surface was polished between each trial.

"Simultaneous Determination Of Copper, Lead, Cadmium, And Zinc In Previously Lyophilized Biological Tissues Using Flow Injection Analysis/anodic Stripping Voltammetry"
Electroanalysis 1994 Volume 6, Issue 10 Pages 894-902
A Izquierdo, M. D. Luque de Castro, M. Valc&aacute;rcel

Abstract: Improvements in three main aspects of the analysis of metal traces in biological tissues are proposed, namely: (a) lyophilization of the samples both to preserve them and to favor the digestion process; (b) digestion of the lyophilized tissues using an effective and fast procedure; and (c) automatic determination of the target analytes by flow-injection analysis/anodic stripping voltammetry (FIA/ASV). After optimization of these steps, the overall procedure was successfully applied to the simultaneous determination of copper, lead, cadmium, and zinc in certified reference materials (CRMs) and fresh bovine liver samples with good results. Finally, the performance of the method was validated by a statistical study using parameters of the certification campaign of the CRMs; the results obtained being within, or close to, the confidence levels of the certification campaign.
Copper Lead Cadmium Zinc Liver Voltammetry Simultaneous analysis

"Lactate Biosensor Based On A Lactate Dehydrogenase/nicotinamide Adenine Dinucleotide Biocomposite"
Electroanalysis 1994 Volume 6, Issue 10 Pages 850-854
Joseph Wang*, Qiang Chen

Abstract: A new biocomposite, fabricated by incorporating lactate dehydrogenase (LDH) and nicotinamide adenine dinucleotide (NAD+) within a graphite-epoxy matrix, is used as a polishable (renewable) and robust biosensor for lactate. Highly sensitive and rapid amperometric biosensing is accomplished at relatively low potentials. The regeneration capability of the biocomposite probe circumvents problems of surface fouling inherent to the detection of NADH. Flow injection detection of lactate, with a sample throughput of 60/h, detection limit of 5 x 10^-4 M, precision of 2.5% (RSD for n = 40), and linearity up to 2 x 10^-2 M, is illustrated.

"Individual And Simultaneous Determination Of Zinc And Cadmium In Biological Tissues By Flow Injection Stripping Voltammetric Analysis"
Electroanalysis 1994 Volume 6, Issue 9 Pages 764-768
A. Izquierdo, M. D. Luque De Castro, M. Valc&aacute;rcel

Abstract: Lyophilized samples were digested as described by Bond et al. (cf. Anal. Chem., 1982, 54, 2318) and analyzed by the cited technique. Detection was performed using a polarograph connected to a wall jet cell with a vitreous working electrode, Ag/AgCl (3 M KCl) reference electrode and Au auxiliary electrode. Before analysis, the working electrode surface was conditioned with a stream of 0.1 µM-Hg(II) (0.2 ml/min) for the deposition of a Hg film at a working electrode potential of -1.0 V vs. Ag/AgCl for 20 min, followed by 0.0 V for 2 min. The stream was then switched to a carrier of 1 M acetate buffer solution (0.2 ml/min) of pH 4.5 into which the sample (600 µL) was injected and a deposition potential of -1.0 V was applied to the working electrode. Three minutes after injection, the flow was halted, and 5 s later a positive differential pulse scan from -1.0-0.0 V (repetition time 0.4 s; pulse amplitude 50 mV; scan rate 40 mV/s) was applied. Detection limits were 0.8 nM and 2 nM for Cd and Zn, respectively, corresponding determination limits were 1 nM and 5 nM. RSD were 1.57% (Cd) and 5.6% (Zn). Results for reference materials agreed with certified values. No interference caused by the formation of intermetallic compounds was detected.
Cadmium Zinc Biological tissue Voltammetry Electrode Electrode Interferences Reference material

"Micromachined Electrochemical Flow Cell For Biosensing"
Electroanalysis 1994 Volume 6, Issue 9 Pages 735-739
Yuji Murakami, Takashi Uchida, Toshifumi Takeuchi, Eiichi Tamiya, Isao Karube, Masayuki Suda

Abstract: A miniaturized flow cell (diagram given) consisting of a glass plate with gold electrodes, a silicon chip with a V-shaped groove and immobilized glucose oxidase was fabricated using micromachining techniques including photolithography, vacuum deposition, anisotropic etching and fusion bonding (details given). All fabrication processes except bonding were successfully performed; anodic bonding techniques may be applicable, however. The device was used for the direct detection of glucose after sample solution was introduced into the cell using the capillary effect (surfactant was added to the solution to enhance the effect). H2O2 produced by glucose oxidase was detected when 700 mV was applied between the counter electrode and one of the working electrodes. A linear response was observed from 0.4-1.0 mM glucose. The device was also applied to FIA. Phosphate buffer of pH 7 (50 µL/min) and sample solution (2 µL) were pumped through the system, applying 500 mV between the electrodes. The system showed a linear response to H2O2 and glucose from 0.2-50 mM and 2-115 mM, respectively. Results for both direct-batch injection and FIA are discussed. The device was suitable for clinical applications.
Glucose Hydrogen peroxide Biological Electrode Flowcell

"Amperometric Flow Injection Analysis Of Purine Nucleotides: Comparison Of Selectivity For Hydrolytic Cleavage Of Purine Nucleotides"
Electroanalysis 1994 Volume 6, Issue 8 Pages 706-710
Toshio Yao *, Kiminori Tsureyama, Taketoshi Nakahava

Abstract: For the detection of purine nucleotides, samples solution was injected into a carrier stream of 0.1 M borate buffer of pH 7.5 containing 5 mM inosine and passed through a hydrolase-immobilized reactor connected in series with a co-immobilized purine-nucleoside phosphorylase/xanthine oxidase reactor. Detection was performed by passing the resulting stream through a flow-through vitreous C electrode supplied with a constant potential (0.6 V vs. Ag/AgCl) and the current was recorded. Flow rates were 2.9 ml/min (details given). The use of four different hydrolase-immobilized reactors (alkaline phosphatase, apyrase, 5'-nucleotidase or ATPase) was investigated with respect to differences in selectivity for the hydrolytic cleavage to purine nucleotides. Using the alkaline phosphatase reactor complete conversion of all purine nucleotides to the corresponding nucleosides was achieved; using the apyrase reactor complete conversion of nucleoside triphosphate and diphosphate to nucleoside monophosphate, was achieved; and using the 5'-nucleotidase reactor selective hydrolytic cleavage of nucleoside monophosphate to nucleoside was achieved. Incomplete conversions were obtained with the ATPase reactor. Results (tabulated) are discussed.
Nucleotides, purine Biological Amperometry Electrode Electrode

"Investigations Of Platinized And Rhodinized Carbon Electrodes For Use In Glucose Sensors"
Electroanalysis 1994 Volume 6, Issue 8 Pages 625-632
Stephen F. White, Anthony P. F. Turner*, Rolf D. Schmid, Ursula Bilitewski, Joanne Bradley

Abstract: Graphite electrodes were modified by the electrodeposition of either platinum or rhodium, using cyclic voltammetry. Following only brief periods of treatment, platinized carbon electrodes were able to directly oxidize glucose at a potential of +350 mV (vs. Ag/AgCl). By narrowing both the potential range of deposition (-450 to -500 mV) and cycling period (50 seconds at a scan rate of 10 mV s-1), the effects of direct glucose oxidation could be significantly reduced. Detection of H2O2 at +400 mV was possible; glucose enzyme electrodes were constructed, with glucose oxidase immobilized in hydroxyethylcellulose, and operated at this potential. These sensors had a linear range of 0.1 to 25 mM glucose and a slope of 8 nA/mM. Other electrodes were prepared by the electrodeposition of rhodium. These base electrodes proved to be insensitive to glucose and produced-higher currents (compared to low platinum electrodes) to H2O2. Glucose sensors were constructed using rhodinked electrodes. Again operating at + 400 mV, these sensors had a linear range from 0.1 to 20 mM and a slope of 21 nA/mM glucose.
Glucose Voltammetry Electrode Electrode Sensor Method comparison

"Surfactant-modified Carbon-paste Electrode. 2. Analytical Performances"
Electroanalysis 1994 Volume 6, Issue 5-6 Pages 459-462
K. Digua, J.-M. Kauffmann, M. Khodari

Abstract: The electrode described in Part I (this issue, Section A) showed a strongly enhanced stripping current with respect to that at an unmodified electrode in the pre-concentration voltammetry of promethazine: after accumulation at an electrode containing 10% of sodium hexadecanesulfonate (I) for 5 min from 5 mM phosphate buffer of pH 2.2, the calibration graph was linear for 35 nM-1.65 µM- and for 1.65-15 µM-promethazine, with a detection limit of 0.5 nM. Current enhancements were also observed for other hydrophobic and cationic species. FIA experiments with the electrode containing I (loc. cit.) and one prepared analogously with hexadecanesulfonic acid indicated the effectiveness of the latter for discriminating against negatively charged species, e.g., ascorbate.
Promethazine Electrode Electrode Voltammetry Interferences Preconcentration

"Amperometric Biosensors For Detection Of L- And D-amino-acids Based On Co-immobilized Peroxidase And L- And D-amino-acid Oxidases In Carbon-paste Electrodes"
Electroanalysis 1994 Volume 6, Issue 5-6 Pages 381-390
V. Kacaniklic, K. Johansson, G. Marko-Varga, L. Gorton, G. J&ouml;nsson-Pettersson, E. Cs&ouml;regi

Abstract: Graphite powder (0.1 g), previously heated at 700°C for 15 s and cooled, was added to a solution of 1 mg each of horse-radish peroxidase and an L- or D-amino-acid oxidase in 0.1 M phosphate buffer of pH 7.0 to which a 0.1% volume of aqueous PEI was then added. The mixture was set aside at 4°C for 2 h and then dried under reduced pressure for 4.5 h, and a paste was formed by addition of 40 µL of paraffin oil and packed to a depth of 3-4 mm in the tip of a 1 mL plastic syringe barrel otherwise filled with non-enzyme-containing carbon paste. The resulting biosensors were used (-50 mV vs. Ag/AgCl) in a flow injection system with 0.1 M phosphate buffer of pH 8.0 as carrier (0.6 ml/min); the responses relative to that for phenylalanine are tabulated for 18 common L-amino-acids. Calibration graphs are also shown, that for H2O2 being slightly curvilinear up to 0.5 mM and those for L-tryptophan, -leucine, -isoleucine, -tyrosine and -phenylalanine up to 5 mM (injection volume 50 µL). Results for analogous D-amino-acid biosensors are also presented.
Amino acids, L Amino acids, D l-Tryptophan l-Leucine l-Isoleucine Tyrosine l-Phenylalanine Sensor Amperometry Electrode Immobilized enzyme Apparatus Detector

"Simultaneous Determination Of Glucose And Sucrose By A Dual-working-electrode Multi-enzyme Sensor Flow Injection System"
Electroanalysis 1994 Volume 6, Issue 5-6 Pages 361-367
Xianen Zhang, Garry A. Rechnitz

Abstract: Two working electrodes, each consisting of carbon paste covered with a cross-linked enzyme membrane, were mounted in a flow injection flow cell (diagram presented). The membrane of the upstream electrode was prepared from glucose oxidase and that of the downstream electrode from glucose oxidase with an outer layer of β-fructofuranosidase/aldose 1-epimerase. A layer of cross-linked catalase was formed on the wall of the flow cell between the two electrode membranes. A 50 µL sample was injected into a carrier stream of phosphate buffer solution (pH 6.8); both electrodes were maintained at 0.9 V vs. Ag/AgCl, so that glucose was detected at the upstream and glucose plus sucrose at the downstream electrode. The method of calculating the two concentrations is described. When the method was applied to Cola beverages, the relative errors for glucose and sucrose were ~3 and ~4%, respectively.
Glucose Sucrose Soft drink Amperometry Electrode Electrode Electrode Sensor

"Kinetic Studies On Membraneless Amperometric Biosensors Prepared From Xanthine Oxidase, Organic Conducting Salt, And Silicone Oil"
Electroanalysis 1994 Volume 6, Issue 4 Pages 305-315
Ulrich Korell, Ursula E. Spichiger

Abstract: A rotating disc electrode (4 mm diameter) based on Kel-F tubing filled with a tetrathiafulvalene-p-tetracyanoquinodimethane (TTF-TCNQ)/Si oil paste (5:8) mixed with xanthine oxidase (15:1), was combined with a Ag/AgCl reference electrode and a Pt wire counter electrode to form an amperometric biosensor. The response to hypoxanthine in pyrophosphate buffer was described by the enzyme-kinetic Michaelis-Menton formalism with good correlation from -100 to +300 mV at pH 6.1-8.8. Xanthine oxidase was oxidized by at least-two mediator species by a homogenous mechanism. The sensor could be operated in air-saturated solution, and operation in flow analysis systems is recommended. The calibration graphs were linear for up to 3 µM-hypoxanthine and the detection limit was ~10 nM. The response time was ~10 s. Ascorbate did not interfere for measurements made at 9 Hz, -75 mV and pH 6.7. The sensor paste was stable for 3 months at -30°C.
Hypoxanthine Sensor Electrode Electrode Amperometry Apparatus Interferences Kinetic

"NADH Electrochemical Sensor For The Enzymatic Determination Of L- And D-lactate And 3-hydroxybutyrate Using A Flow Injection Analysis"
Electroanalysis 1994 Volume 6, Issue 3 Pages 221-226
G. Marrazza, A. Cagnini, M. Mascini

Abstract: The NADH sensor was prepared from spectroscopic graphite (2 cm x 3 mm) assembled in a wall-jet cell using a FIA procedure and was coupled with enzyme reactors. The reactors were prepared by immobilizing L-, D-lactate or 3-hydroxybutyrate dehydrogenases on to aminopropyl-controlled pore glass beads using glutaraldehyde in a packed-bed enzyme reactor. Measurements were performed at an applied potential of +500 mV vs. Ag/AgCl. 3-hydroxybutyrate and L- and D-lactate were oxidized in the presence of NAD+ and the NADH produced was measured. By the appropriate choice of buffer, pH and NAD+ concentration, the analytes could be measured in the range 1 x 10^-6 to 1 x 10^-4 M in a few seconds. Calibration graphs are shown.
d-Lactate l-Lactate 3-hydroxybutyrate Biological Sensor Controlled pore glass

"Amperometric Detection Of Purine Nucleotides Utilizing Immobilized Enzyme Reactors And Online Amplification By Substrate Recycling"
Electroanalysis 1994 Volume 6, Issue 2 Pages 165-169
Toshio Yao, Kiminori Tsureyama

Abstract: Purine nucleotides were detected using a FIA system previously described (Yao et al., Anal. Chim. Acta, 1990, 238, 339). An alkaline phosphatase immobilized reactor (18 mm x 3 mm i.d.) was positioned in series before a coimmobilized purine-nucleoside phosphorylase-xanthine oxidase reactor (27 mm x 3 mm i.d.) and a flow-through glassy carbon electrode. A carrier solution of 0.1 M borate buffer containing 5 mM inosine and 1 mM MgCl2 was used at a flow rate of 0.5 ml/min. Online amplification of the purine nucleotides was performed using an alkaline phosphatase/purine-nucleoside phosphorylase/xanthine oxidase reactor. Calibration graphs for the amplified nucleotides were linear up to 10 µM with a detection limit of 40 nM. The RSD (n = 7) were 2.2-3.8% for 0.1 µM.
Nucleotides, purine Biological Amperometry Electrode Immobilized enzyme

"Electrocatalytic Flow Detection Of Amino Acids At Ruthenium Dioxide-modified Carbon Electrodes"
Electroanalysis 1994 Volume 6, Issue 2 Pages 125-129
Joseph Wang*, Yuebe Lin

Abstract: Fixed-potential anodic detection of ammo acids and peptides can be carried out at ruthenium dioxide (RuO2) -modified carbon paste and graphite epoxy electrodes. The effect of various experimental variables on the electrocatlytic response is explored. Optimal detection is obtained under strongly alkaline conditions and a low ( + 0.45 v vs. Ag/AgCl) operating potential. With flow injection, the response is fast, linear, and reproducible )relative standard deviations of 1.5 to 1.7%, n = 32). Similar advantages are reported for the incorporation of cobalt oxide (CO3O4) into carbon paste detectors.

"Electrooxidation Of Ascorbic Acid At The Bis(4-pyridyl) Disulfide Modified Gold Electrode"
Electroanalysis 1994 Volume 6, Issue 2 Pages 119-123
Yuanwu Xie, Shaojun Dong

Abstract: A Au disc working electrode was modified by dipping the freshly polished electrode into 1 mM bis(4-pyridyl) disulfide for 2 min. The electrode was used for the study of the electro-oxidation of ascorbic acid using a Ag/AgCl (saturated KCl) reference electrode and a Pt wire counter electrode. The oxidation process was pH dependent due to the static interaction between ascorbic acid and the modified electrode surface. At 0.005-2 mM the peak currents show a good linear relationship with the concentrations of ascorbic acid. The modified electrode has greater stability and can be used in FIA.
Ascorbic acid Environmental Electrode Electrode Electrode

"Ammonium Detection Using An Ion-selective Electrode Array In Flow Injection Analysis"
Electroanalysis 1994 Volume 6, Issue 1 Pages 9-16
F. J. S&aacute;ez de Viteri, Dermot Diamond *

Abstract: Due the low selectivity of the nonactin NH4+ ISE toward some common ions, especially K+, an array of ISE selective for NH4+, Na+, K+ and Ca2+ was used as the FIA detector. Preparation of the PVC-based membranes described and the FIA system is shown schematically. A Ag/AgCl flow-through electrode, through which saturated KCl was continuously pumped was used as the reference system. After conditioning the system overnight (details given), sample (50 µL) was injected and mixed with the carrier stream (1 ml/min) comprising 0.01 M Tris hydrochloride buffer of pH 7.2-7.5/0.1 µM-cation solution containing ammonium, sodium, potassium and calcium chloride solution The resulting peaks were recorded. The whole system was interfaced to a PC (details given) and the array response was modelled using the Nikolskii-Eisenmann equation and the Projection Pursuit technique. The latter method gave the best results in the activity range 0.1-10 mM. The sensor array gave improved results for NH4+ determination in aqueous samples in the activity range 0.01-10 mM compared to the use of a single NH4+ electrode.
Ammonium Environmental Electrode Electrode Electrode Electrode

"Electrochemical Detection As An Alternative To UV In RP-HPLC Peptide Mapping"
Electroanalysis 1994 Volume 6, Issue 1 Pages 1-8
L. Chen, I. S. Krull *

Abstract: A 0.5 mL portion of cytochrome C solution, as an e.g., (2 mg/mL in 100 mM NH4HCO3 buffer, pH 8) was mixed with 0.5 mL of trypsin (0.1 mg/mL) and incubated at 37°C for 24 h. After digestion, the sample was frozen in a dry ice/acetone mixture and lyophilised at -40°C for 24 h and dissolved in water. A 20 µL portion of the solution was analyzed by HPLC on a YMC AP-303 S-5 300A ODS column (25 cm x 4.6 mm i.d.) equipped with a Supelguard LC-18 pre-column (2 cm) with gradient elution (flow rate not given) with propan-2-ol/methanol/H2O/trifluoroacetic acid/100 mM phosphate buffer of pH 2.8-4.5 (details given). Electrochemical detection was performed with a dual vitreous C working electrode, a stainless-steel auxiliary electrode and a Ag/AgCl reference electrode. Post-column derivatization was performed in a knitted open tubular reactor knitted with PTFE tubing (16 x 0.5 mm i.d.) wrapped around a Hg lamp at 254 nm. Using photoradiation some non-electroactive amino-acids and peptides can be made electroactive increasing the sensitivity and selectivity of the electrochemical detection. Sensitivity was improved by one order of magnitude over UV detection.
Peptides HPLC Electrode Post-column derivatization Knotted reactor Open tubular reactor Photochemistry

"Simultaneous Determination Of Phosphate And Pyrophosphate By An Amperometric Flow Injection System With Immobilized Enzyme Reactors"
Electroanalysis 1993 Volume 5, Issue 9-10 Pages 887-890
Toshio Yao, Tamotsu Wasa

Abstract: A FIA method is described for the determination of phosphate and pyrophosphate. The sample is split so that half passes through an immobilized inorganic pyrophosphate reactor before passing through a co-immobilized nucleoside phosphorylase-xanthine oxidase reactor. The other half of the sample passes only through the co-immobilized reactor. As each channel has a different residence time, two peaks are obtained; the first corresponds to phosphate, the second to phosphate plus pyrophosphate. The procedure was carried out at 37°C and detection was at 0.5 V vs. Ag/AgCl. The detection limits were 1 µM-phosphate and 2 µM-pyrophosphate. Sample throughput was 20/h with RSD of 1.5%. The co-immobilization method was silmilar to that described previously (Yao and Matsumoto, Ibid., 1989, 1, 173).
Phosphate Pyrophosphate Amperometry Immobilized enzyme

"Rare-earth Ion-selective Electrodes"
Electroanalysis 1993 Volume 5, Issue 9-10 Pages 863-867
Yonghua Zhang, Jinlan Wu, Erkang Wang

Abstract: Copolymers obtained by radiation grafting of high-density polyethylene, polypropene, PVC, polystyrene or polyacrylonitrile with acrylic acid were treated with a solution of rare-earth chloride by IR heating for 18 h, and the resulting materials were heat-pressed to form membranes for use in ISE. Membranes incorporating Gd, Pr, Nd or Yb, used at the optimum pH of 4.5-6.5, 5.5-6.4, 5.5 and 5.5-6.5, respectively, had corresponding linear response ranges of 0.002-10 mM, 0.5-100 mM, 0.002-10 mM and The membranes could be used in a flow-through cell detector for FIA. The selectivity coefficients for a Gd-selective electrode are tabulated. Electrodes were also prepared from ignited rare-earth oxides; e.g., 50-56% of cerium oxide was mixed with epoxy-resin and carboxy-terminated butadiene-acrylonitrile copolymer to form a Ce electrode for the range 10 µM-0.1 M Ce3+, -La3+, -Nd3+, -Pr3+ or -Sm3+. Electrodes based on lanthanum oxide or Dy2O3 were also prepared. Chelates of Nd with 4-benzoyl-3-methyl-1-phenylpyrazolin-5-one, Yb with 2-ethylhexyl 2-ethylhexylphosphate and Sm(NO3)3 with TBP were used to prepare Nd, Yb and Sm electrodes, respectively.
Praseodymium Neodymium Ytterbium Gadolinium Electrode Electrode Electrode Electrode Electrode Selectivity Detector

"Sequential Flow Injection Potentiometric Determination Of Iodide And Iodine In Povidone-iodine Pharmaceuticals"
Electroanalysis 1993 Volume 5, Issue 9-10 Pages 855-861
Saad S. M. Hassan, Sayed A. M. Marzouk

Abstract: A solution of PVC, tris-(4,7-diphenyl-1,10-phenanthroline)iron(II) di-iodide complex (ionophore) and 2-nitrophenyl phenyl ether (plasticizing mediator) in THF was incorporated in a flow-through sandwich potentiometric cell (Hassan and Ahmed, J. AOAC, 1991, 74, 900). The sensor displayed a fast response (10-30 s) for 0.006-100 mM iodide over the pH range 1-11; the detection limit was 0.5 µg/ml. To determine iodide and iodine in povidone-iodine pharmaceuticals, sample solution was injected into a sodium sulfate/ascorbic acid stream followed by injection into a second stream of alkaline resorcinol. The iodine concentration. was calculated from twice the difference between the first and the second signal, and the iodide concentration. was obtained from twice the second signal less the first signal. For pharmaceuticals containing 1.1-9.1 mg/ml of iodine and 1.2-7.2 mg/ml of iodide, the mean standard deviations were 0.07 and 0.06 mg/ml, respectively (n = 3).
Iodide Iodine Pharmaceutical Potentiometry

"Iodide-selective Electrodes Based On A Mercury - Tri-isobutylphosphine Sulfide Complex"
Electroanalysis 1993 Volume 5, Issue 9-10 Pages 839-843
Sylvia Daunert, Antonio Florido, Jordi Bricker, Wes Dunaway, Leonidas G. Bachas, Manuel Valiente

Abstract: Tri-isobutylphosphine sulfide - Hg complex-based ISE were prepared (described) and were used in conjunction with an Orion 90-02-00 double-junction reference electrode. Batchwise potentiometric measurements were made in 0.1 M 2-morpholinoethanesulfonic acid (I)/NaOH buffers of pH 5.5, 6 or 6.5 or 0.1 M NaH2PO4/NaOH buffers of pH 6 or 6.5. Various Hg complex/PVC/plasticizer/DMF/THF mixtures were also used to prepare a membrane within a flow-through tubular electrode made from Epo-Tek 410 Ag-based conductive epoxy. This membrane electrode was used for detection in FIA. ISE containing 4% of ionophore showed near-Nernstian response to thiocyanate in all three I buffers and the detection limit was 2-4 µM, slightly better than in the phosphate buffers (detection limit of 5 µM-thiocyanate). Response times averaged 1 min for thiocyanate and 12 min for iodide. In FIA, the best signals were obtained with 100 µL sample injections and a carrier flow rate of 3.3 ml/min; with a membrane containing 4% of ionophore, the peak heights were reproducible to within ±1 mV for three injections at a given concentration.
Thiocyanate ion Iodide Electrode Potentiometry

"Bienzyme Sensors Based On"
Electroanalysis 1993 Volume 5, Issue 9-10 Pages 825-831
T. J. Ohara, M. S. Vreeke, F. Battaglini, A. Heller

Abstract: Bilayer electrodes were prepared from NaIO4-oxidized horse-radish peroxidase (described). The outer layer comprised alcohol, choline, glucose, lactate or D-amino-acid oxidase, appropriately immobilized (e.g., by glutaraldehyde; details given). Single-layer electrodes were prepared similarly but with addition of the oxidase enzyme. Electrochemical measurements were carried out in conjunction with a Pt-wire auxiliary electrode and a reference SCE on a Princeton Applied Research model 173 potentiostat/galvanostat under air and at room temp.; the disc electrode was rotated at 1000 rpm and was typically poised at 0 V, the current being measured as a function of time. The electrodes were also used in a wall-jet cell in conjunction with vitreous carbon electrodes for detection in FIA with phosphate buffer solution of pH 7.5 as carrier. The single-layer electrodes could be used in the determination of alcohols, choline and D-amino-acids and bilayer electrodes were more stable than the single-layer electrodes. In FIA with a bilayer lactate electrode, calibration graphs were linear for 0.2-1.8 mM lactate and each analysis took 90 s.
Electrode Electrode Electrochemical analysis Sensor Enzyme Redox

"Cholesterol Biosensors Prepared By Electropolymerization Of Pyrrole"
Electroanalysis 1993 Volume 5, Issue 9-10 Pages 753-763
Wolfgang Trettnak, Ilaria Lionti, Marco Mascini

Abstract: Platinum electrodes (1.75 mm diameter) were polished with alumina and rinsed thoroughly with water. Electropolymerization of cholesterol oxidase in pyrrole was carried out from a solution containing 10 mM NaClO4, 0.1 M pyrrole and 15-55 iu/ml of enzyme in 0.1 M phosphate buffer of pH 7, which was purged with N2 before applying a potential of 800 mV to the Pt electrode. The resulting biosensor was covered with a polycarbonate membrane (pore size 3 µm) and conditioned at 700 mV in 0.1 M phosphate buffer of pH 7. Measurements of cholesterol were carried out at 700 mV in the same buffer containing 1% of Triton X-100. The biosensor was applied in batch mode and in flow-through and flow injection analyzes with 1% Triton X-100 as carrier for detection of the H2O2 formed in the enzymatic reaction. In flow injection analysis with a 50 µL injection and a flow rate of 0.2 ml/min, the response was linear up to 250 µM-cholesterol; the detection limit was 5 µM and the sample throughput was 25/h. Interference by uric acid was fairly slight but that by ascorbic acid was severe.
Cholesterol Electrode Sensor Detector Interferences Triton X Surfactant

"Postchromatographic Electrochemical Detection Of Carbohydrates At A Silver Oxide Electrode"
Electroanalysis 1993 Volume 5, Issue 8 Pages 669-675
Terrence P. Tougas, Mark J. Debenedetto, James M. Demott Jr.

Abstract: An oxide surface was formed on a 2-mm Ag-wire electrode by conditioning in 0.1 M NaOH at +0.7 V for 30 min and then at 0.45 V vs. the SCE. The properties of the electrode were studied and it was applied to the electrochemical detection of simple sugars separated by HPLC on a Waters carbohydrate analysis column (30 cm x 3.9 mm) with mobile phase (1 ml/min) of acetonitrile/phosphate buffer of pH 8 (36:11) and by FIA. Calibration graphs were rectilinear for 1-100 µM-galactose, glucose, ribose and xylose.
Carbohydrates Glucose Ribose Galactose Xylose Electrode Electrochemical analysis HPLC Post-column derivatization

"Comparison Of Detector Cell Configurations In Flow Injection Potentiometry"
Electroanalysis 1993 Volume 5, Issue 7 Pages 581-588
David E. Davey, Dennis E. Mulcahy, Gregory R. O'Connell

Abstract: A solid-state iodide-selective electrode was used to compare the performances of flow-through, edge-jet and wall-jet detector cell configurations in FIA. Cell volume of 4-210 µL were studied with flow streams of 1.7 or 3.2 ml/min and injections of 0.1 M KI were made into a flow stream of 10 µM-KI or of 0.1 M KNO3. Similarly good results were obtained for each configuration in the cell volume range 4-63 µL at 1.7 ml/min or 4-120 µL at 3.2 ml/min, but best results were given generally under thin-layer flow conditions which occurred in the cell volume range 4-33 µL. The range of cell volume that could yield steady data decreased in the order edge-jet, wall-jet, flow-through configuration.
Iodide Potentiometry Electrode Method comparison

"Graphite-Teflon Enzyme Electrode"
Electroanalysis 1993 Volume 5, Issue 7 Pages 575-579
Joseph Wang *, A. Julio Reviejo, Lucio Angnes

Abstract: The preparation and performance of bulk-modified composite graphite-PTFE enzymatic electrodes and their modification by incorporation of horse-radish peroxidase (to detect peroxides), glucose oxidase (to detect glucose) or ferrocene (to provide a reagentless electrode) are described. The peroxide electrode could be used to determine H2O2 by FIA in 0.05 M phosphate buffer (pH 7.4) to a detection limit of 2.5 µM with an operation rate of up to 120 samples/h and RSD of 2%. The composite electrodes provided fast response and good signal-to-noise ratios and could be renewed by polishing.
Electrode Graphite Enzyme

"Effect Of Polymer Composition On The Detection Of Electro-inactive Species Using Conductive Polymers"
Electroanalysis 1993 Volume 5, Issue 7 Pages 555-563
Omowunmi A. Sadik, Gordon G. Wallace

Abstract: Polypyrrole electrodes were prepared by galvanostatically electropolymerizing pyrrole monomer (0.1M) from aqueous solution on to Pt. Counter-ion solution for polymerization contained 0.5 M chloride, acetate, dodecylsulfate, phosphate or carbonate. Current densities of 0.85 mA/cm2 were used, with deposition of polypyrrole for 5 min. A study was made of the effects of polymer composition, nature of eluent and electrochemical waveform on the selectivity of detection of electro-inactive species. Sensitivities of the electrodes to each cited counter-ion species during FIA in a stream of 1 M glycine were assessed.
Electrode Detector

"Liquid Chromatography And Electrochemical Detection Of Organic Peroxides By Reduction At An Iron Phthalocyanine Chemically Modified Electrode"
Electroanalysis 1993 Volume 5, Issue 7 Pages 547-554
Xiaohe Qi, Richard P. Baldwin

Abstract: Iron phthalocyanine (2%) was incorporated into carbon paste to form an electrode that could be used in 0.05 M phosphate buffer at pH 2 for the amperometric detection of organic peroxides (excluding dialkyl peroxides) at +0.1 V (minimum) vs. Ag/AgCl. Detection limits (pmol) measured for operation at +0.35 V ranged from 0.13 for peracetic acid to 300 for 1-[(1-hydroperoxycyclohexyl)dioxy]cyclohexanol. No response was shown for a 500-pmol injection of t-butyl peroxide, but the detection limit was 1.0 pmol for 2-butanone peroxide. The method was suitable for use in FIA or HPLC and 10% acetonitrile could be added to the mobile phase.
Peracetic acid 1-[(1-hydroperoxycyclohexyl)peroxy]cyclohexanol 2-Butanoneperoxide Electrode Electrode

"Electrochemical Oxidation Of Penicillins On Gold Electrodes"
Electroanalysis 1993 Volume 5, Issue 5-6 Pages 473-482
Lisa Koprowski, Eric Kirchmann, Lawrence E. Welch

Abstract: The electrochemical oxidation of penicillins at Au electrodes was optimized; the best sensitivity was observed in strongly acidic solution, but the chemical stability was insufficient for use under these conditions. Use of a weakly acidic acetate buffer solution yielded sufficient stability at the cost of some sensitivity. By the application of pulsed amperometric detection, the penicillins could be monitored either directly or indirectly, depending on the specified waveforms. Cyclic voltammetry was performed with use of Ag/AgCl reference electrodes, solid metal working electrodes and a Pt-wire counter electrode. Direct detection by standard pulsed amperometry was the best detection method; when this was used in a flow injection system, the RSD for peak height was 0.1% and the detection limit for benzylpencillin was 0.4 µM.
Penicillin Electrode Amperometry Redox

"Selective Biocatalytic Measuring Cell For Flow Injection Analysis"
Electroanalysis 1993 Volume 5, Issue 4 Pages 277-281
J&oacute;zsef Tarcali, G&eacute;za Nagy*, Ern&ouml; Pungor

Abstract: The cell described amperometrically detects H2O2 formed in an enzyme-catalyzed oxidation reaction with various substrates. The cell is manufactured from Plexiglas and consists of an electrode assembly mounted in a cylindrical channel (1.5 mm diameter). The carrier electrolyte solution flows through the channel and around the electrode assembly. The electrode assembly is constructed from a dialysis tube (200 µm o.d., wall thickness 11 µm) filled with enzyme solution and containing a Pt wire electrode. The operation of the cell was tested with two model compounds (ethanol and glucose) and two corresponding enzymes. Calibration graphs were rectilinear from 30 to 80 mM glucose and 0.1 to 20 mM ethanol. The limits of detection were 1.8 to 4 µM-glucose and 0.1 to 0.5 mM ethanol.
Glucose Ethanol Amperometry Electrode Sensor Enzyme Catalysis Dialysis

"Glassy Carbon Electrodes Coated With Electropolymerized Resole Pre-polymer Mixtures: Amperometric Response To Phenols And Application As Chromatographic Sensors"
Electroanalysis 1993 Volume 5, Issue 2 Pages 165-169
Patricia I. Ortiz, Paul R. Abu Nader, Horacio A. Mottola

Abstract: The electropolymerization of 4-hydroxybenzaldehyde and formaldehyde on glassy C gave amperometric sensors that were protected from surface poisoning. The electrodes were housed in a thin-layer cell in an unsegmented continuous-flow system, with 0.010 M phosphate buffer (pH 7.40) - 0.050 M KCl as the carrier (0.90 mL min-1). The response of a range of phenolic compounds at an applied potential of +0.650 V is reported and the results were compared with those obtained by electrochemical detection after post-column enzyme reaction. The polymer-coated electrode had greater sensitivity, and trends observed on changing the substituent groups are discussed. The electrodes were used as electrochemical detectors in the HPLC separation of phenols on a column (25 cm x 4.6 mm) of Econosphere C8 (5 µm), with methanol - acetonitrile - 0.030 M ammonium acetate buffer of pH 5 (7:34:59) as the mobile phase (1 mL min-1) and detection at an applied potential of +0.900 V vs. Ag - AgCl, 3 M NaCl, cross-referenced with UV detection at 280 nm. The response was rectilinear from 0.1 to 10 µM-phenolic species. The stability of the polymeric film was excellent over more than a week of continuous use but it does depend on the film thickness.
Phenols Amperometry Electrode HPLC Sensor Enzyme

"Cobalt(II, III)-oxide Chemically Modified Electrode As Amperometric Detector In Flow Injection Systems"
Electroanalysis 1993 Volume 5, Issue 2 Pages 145-148
S. Mannino, M. S. Cosio, S. Ratti

Abstract: A mixture of Co oxides was blended with C paste (graphite powder - oil - oxide; 5:4:1) and packed in the cavity of a flow detector. Constant-potential amperometry in a flow system was used to examine the suitability of the modified electrode for the detection of biologically important substances. The mobile phases were 0.1 M NaOH, 0.1 M phosphate buffer of pH 7 and 0.1 M acetate buffer of pH 5.5 (1.5 mL min-1). The overvoltage for the oxidation of compounds such as glucose and other sugars, H2O2 and cysteine was greatly reduced. The modified electrode was stable, could be easily renewed and gave reproducible results. The responses of 14 compounds at -300 to +600 mV are tabulated. When operated at -300 mV, the electrode could be used for the determination of H2O2 in milk, even in the presence of other naturally reducing substances. Changing the potential to +400 mV allowed the determination of lactose in the same sample.
Cobalt Lactose Glucose Amperometry Electrode

"Flow Injection Potentiomentric Determination Of Creatinine In Urine Using Sub-Nernstian Linear Response Range"
Electroanalysis 1993 Volume 5, Issue 2 Pages 113-120
Wojciech Matuszewski, Marek Trojanowicz, Mark E. Meyerhoff, Anna Moszczyska, Elzbieta Lange-Moroz

Abstract: The split-stream flow injection system is based on the use of a micro-reactor containing creatinine iminohydrolase immobilized on porous glass beads. Urine (20 µL) was injected into a carrier stream of water (2 mL min-1) and merged with 50 mM phosphate buffer (pH 7.0) containing 20 mM KCl and 40 mM NaCl. This stream was split into two channels; one was passed through a short length of tubing to a nonactin-based membrane electrode which detected NH4+ ions and the other flowed through the enzyme reactor followed by a longer tube as a delay loop prior to passing through the detector. The split sample zone and addition of alkali metal ions allowed simple correction for endogenous NH4+. A rectilinear response was obtained for creatinine, even up to 80 mM NH4+. Recoveries were >99% and the coefficient of variation (n = 10) were 1.48%.
Creatinine Urine Potentiometry Electrode Cellulose nitrate Immobilized enzyme

"Flow Monitoring Of Glutamate And Aspartate In Foods And Pharmaceutical Products With Immobilized Bienzyme Electrochemical Cells"
Electroanalysis 1992 Volume 4, Issue 9 Pages 851-857
G. Palleschi*, M. G. Lavagnini, D. Compagnone, P. Bertocchi, D. Moscone

Abstract: Electrochemical thin-layer and wall-jet amperometric cells incorporating an Immobilon-AV immunoaffinity membrane on which L-glutamate oxidase and aspartate aminotransferase were covalently co-immobilized were used in continuous-flow and flow injection analysis. The flow-through system gave higher sensitivity and the flow injection system gave better reproducibility and faster response. The wall-jet cell was the more suitable for flow injection analysis. The flow injection technique was used to determine glutamate (I) in foods and aspartate (II) in pharmaceuticals. The calibration graphs were rectilinear for 1 to 500 and 10 to 500 µmM of I and II, respectively; corresponding detection limits were 1 and 5 µM. Results correlated well with those obtained by HPLC. Electrochemical enzyme cells for glutamate and aspartate anal. have been assembled and used in continuous-flow and in flow injection analysis. The enzymes, glutamate oxidase (GOD) and aspartate amino-transferase (AST), were co-immobilized on an Immobilon Immuno-affinity membrane, which was placed into a three-electrode, flow-through cell. Additional protective membranes were used to reduce the electrochemical interferences and to protect the immobilized enzymes. Thin-layer and wall-jet cells were used and compared. Calibration curves for glutamate and aspartate showed a linearity range of 1-500 µmol/L and 10^-500 µmol/L respectively. The sensitivity was higher using the flow-through system with a response time of 2 min. Better reproducibility was achieved using the FIA procedure with a response time of less than 1 min. Glutamate in food and aspartate in some pharmaceutical products were determined Results were compared and correlated well with an HPLC procedure.
Glutamate Aspartate Food Pharmaceutical Electrode Method comparison Immobilized enzyme Interferences

"Potentiometric Detectors For The Determination Of Acidity By Discontinuous Flow Analysis"
Electroanalysis 1992 Volume 4, Issue 8 Pages 805-810
Terence J. Cardwell, Robert W. Cattrall, Gregory R. O'Connell, John D. Petty, Geoffrey R. Scollary

Abstract: Three potentiometric detectors, each incorporating a vibrating reed mixer, were investigated for use in the determination of acidity by discontinuous flow anal. (DFA). Two of these used PVC and glass membrane pH-sensors, and the third employed a novel differential titration technique based on two quinhydrone electrodes. These detectors were applied to the determination of the total acidity of vinegars and the titratable acidity of wines, the results agreeing well with standard procedures. The anal. of wine proved to be difficult because of the gradual change in pH at the end-point and so a method was developed which determined the titratable acidity at pH 8.3.
Acidity Food Wine Electrode Electrode Potentiometry Mixing Method comparison

"Amperometric Response Of Mediating Layers On Electrode Surfaces To Gaussian Concentration Profiles In Flowing Streams"
Electroanalysis 1992 Volume 4, Issue 8 Pages 751-756
John F. Cassidy, William Breen, Anthony McGee, Johannes G. Vos, Michael E. G. Lyons

Abstract: A model is presented for a semi-porous layer containing catalytic sites, coated on an electrode and used for the mediation of analytes. The coated electrodes are applicable as detectors in flow injection analysis or HPLC. Thin layers with high catalyst loading and high rates of electron exchange led to rectilinear graphs of peak current vs. concentration. for chemically modified electrodes in flowing streams. A model for a layer, containing catalytic centers, coated on an electrode and used for the mediation of analyte in a flowing stream is proposed and solved. The model applies to a situation of a Gaussian concentration. profile of analyte impinging on the outer edge of the mediating layer. The important parameters that limit the current magnitude are the diffusion coefficient of the analyte through the layer, the effective electron diffusion coefficient through the layer, and the rate of reaction between the mediator and the analyte. Literature data showed that layers, high catalyst loading, and high rates of electron exchange lead to linear peak current height vs. concentration. plots.
Electrode Electrode Amperometry Apparatus Detector Diffusion coefficients Modeling Peak analysis

"Automatic Mercury Drop Electrode With Double Solenoid Activated Valve"
Electroanalysis 1992 Volume 4, Issue 6 Pages 635-642
Jairo Pedrotti, Lucio Angnes, Ivano G. R. Gutz*

Abstract: The construction and evaluation of a simple, low cost, and versatile automatic mercury electrode, working as dropping (DME), hanging (HMDE), or static drop electrode (SMDE), is described. Fast action of the needle valve is obtained with two solenoids, one for opening the valve and the other for closing it. The electrode can be controlled from a microcomputer or with a digital circuit. The performance of this electrode compares favorably with that of commercial ones in terms of area reproducibility (SD < 0.05%), response time of the valve, current profile during potentiostatic extrusion of the drop, and flexibility of use.

"Unsegmented Flow Systems As Interfaces Between Samples And Electrochemical Detectors"
Electroanalysis 1992 Volume 4, Issue 6 Pages 601-613
M. D. Luque de Castro

Abstract: A review is presented, with 88 references, of the use of electrochemical detectors in flow injection analysis, with emphasis on miniaturization, automation, continuous separation and special applications.
Electrochemical analysis Review Miniaturization Automation

"Simultaneous Flow Injection Analysis For L-lactate And L-malate In Wine Based On The Use Of Enzyme Reactors"
Electroanalysis 1992 Volume 4, Issue 5 Pages 545-548
Shuichi Yoshioka, Hiroyuki Ukeda, Kiyoshi Matsumoto, Yutaka Osajima

Abstract: Malate dehydrogenase and diaphorase were co-immobilized on CNBr-activated Sepharose 4B; lactate oxidase was immobilized on Amino-Cellulofine. The product was packed into a glass tube (10 cm x 2 mm) to form a reactor for malate or lactate, respectively, which was incorporated into one line of a flow injection system operated at 20°C. The sample solution was diluted with 0.05 M pyrophosphate buffer of pH 9.0 and saturated with menadione, then pumped through the sample loop (150 µL) of the lactate line and mixed with 5 mM NAD+ in the same buffer before reaching the sample loop (150 µL) of the malate line. By means of a 16-way switching valve, sample solution was simultaneously injected into the two lines and transported by a stream (2.0 and 1.0 mL min-1 in the lactate and the malate line, respectively) of the pyrophosphate buffer saturated with menadione to the enzyme reactors and thence to an O electrode operated at -0.8 V for amperometric measurement. Peak currents were rectilinearly related to concentration. for 0.05 to 1.2 mM L-malate and 0.01 to 0.5 mM L-lactate. Sampling frequency was 15 h-1. The method was used for determining both analytes in wine; red wines were pre-treated with gelatin to remove polyphenols. Results agreed with those obtained by the conventional F-kit method. The simultaneous determination of L-malate and L-lactate, by enzyme-supported flow injection analysis was developed using 2 enzyme reactors in parallel and a single O2 electrode. NADH formed in the reaction of malate dehydrogenase (MDH) was regenerated to NAD+ with dissolved O2, using vitamin K3 and diaphorase (DI). L-Lactate was determined using the enzyme lactate oxidase (LOD). When sample solutions were simultaneously injected into the 2 reactors (the MDH-DI-reactor and the LOD-reactor) with a controlled residence time, a train of 2 peaks corresponding to L-lactate and L-malate was seen. The peak currents were linearly related to the L-malate and L-lactate concentration. in the range 0.05-1.2 mM and 0.01-0.5 mM, respectively. The present system was applied to the determination of L-lactate and L-malate in wine. The results showed good agreement with those obtained using a conventional method (F-kit method), suggesting that this system may be applicable to the monitoring of malolactic fermentation during wine prodn.
l-Lactate l-Malate Wine Amperometry Electrode Reactor Immobilized enzyme Sepharose beads Merging zones Method comparison

"Multi-enzyme-containing Tissue-based And Ferrocene-mediated Bioelectrode For The Determination Of Polyamines"
Electroanalysis 1992 Volume 4, Issue 5 Pages 521-525
Meng Shan Lin, Minoru Hare, Garry A. Rechnitz

Abstract: Ground oat seedling tissue (which contains polyamine oxidase and peroxidase) was mixed with 2 to 9% (w/w) of graphite - mineral oil (3:2) paste containing 2% of ferrocene, and the mixture was firmly packed into the cavity of a flow cell electrochemical detector or, for steady-state experiments, into the end of a tubular electrode (3 mm i.d.). The electrode tip was smoothed on paper. Polyamine oxidase catalyses the oxidation of polyamines, O as co-substrate is reduced to H2O2, and the peroxidase then oxidizes ferrocene to ferricinium at the expense of H2O2; the signal is monitored reductively at 0.0 V vs. Ag - AgCl. Steady-state amperometric and cyclic voltammetric experiments were carried out in conjunction with a Pt-wire counter electrode; for a working electrode containing 7% of oat seedling tissue, response to spermidine or spermine in 0.1 M phosphate buffer of pH 7 was rectilinear up to 15 or 7.5 µM, respectively, and the corresponding detection limits were 0.19 and 1.15 µM. In the flow injection analyzes, carried out with the same buffer, the Ag - AgCl reference electrode was placed in a compartment downstream of the flow cell, with a stainless steel auxiliary electrode downstream of this, and PTFE tubing was used. Response to spermidine or spermine was rectilinear up to 20 or 15 µM, respectively. The electrodes did not respond to injections of 0.1 µM-ascorbic acid, uric acid, histamine, 4-aminobutyric acid or agmatine.
Amines, poly Spermidine Spermine Sensor Electrode Interferences

"Determination Of 2-thiothiazolidine-4-carboxylic Acid In Urine By Liquid Chromatography With Electrochemical Detection"
Electroanalysis 1992 Volume 4, Issue 4 Pages 515-519
Anton Ciucu, Richard P. Baldwin*

Abstract: An assay procedure utilizing liquid chromatography and amperometric detection at a chemically modified electrode (CME) has been developed for the determination of 2-thiothiazolidine-4-carboxylic acid (TTCA) in urine samples. The electrocatalytic activity of the CME, which consisted of a glassy carbon surface coated with an electropolymerized cobalt phthalocyanine film, permitted optimum response at a potential of +0.75 V vs. Ag/AgCl with a detection limit of 7 pmol for TTCA and with no sample preparation required. In case of fouling of the electrode surface by sample constituents, the polymeric cobalt phthalocyanine electrode surface could be renewed with a variability of less than 10% and an equilibration time of less than 15 minutes.

"Convection-independent Detection With Voltammetric Single Micro-disc Electrodes"
Electroanalysis 1992 Volume 4, Issue 4 Pages 501-506
Frank-Michael Matysik, Hendrik Emons

Abstract: The design and construction are described of a new electrochemical flow cell incorporating a Pt micro-disc electrode that is positioned inside a narrow tube facing into the flowing stream. In experiments with ferrocene as model analyte and 0.1 M tetrapropylammonium perchlorate in acetonitrile as supporting electrolyte, it was shown that the flow rate dependence of the voltammetric signal was reduced as the electrode diameter was decreased from 114 µm, the limiting case being obtained at an electrode diameter of 0.7 µm. However, limits of detection were higher at electrodes smaller than 38 and 8 µm in diameter for continuous-flow and flow injection conditions, respectively. It is concluded that the optimum electrode size needs to be selected with respect to the analytical demands, i.e., the concentration. range of interest and convective characteristics of the experimental system.
Ferrocene Voltammetry Electrode Electrode Optimization Apparatus Detector

"Cross-correlation With Digital Techniques In Flow Injection Analysis And High Performance Liquid Chromatography"
Electroanalysis 1992 Volume 4, Issue 4 Pages 495-500
D. J. Curran, R. E. McKeans

Abstract: Digital signal processing techniques were applied in demonstrating the use of cross-correlation procedures in order to improve the signal-to-noise ratio in measurements involving analogue detectors in flowing streams. Two examples of the technique are presented as illustrations. The first involves the amperometric detection of dopamine in a flow injection procedure wherein the reference and analyte signals are digitized and cross-correlation performed by software using the fast FT technique. The second example concerns the HPLC analysis of a mixture of norepinephrine, L-dopa, dopamine (I) and epinephrine (II) on an Adsorbosphere C-18 column (15 cm x 4.6 mm) with methanol - 0.05 M phosphate buffer (8:92; pH 3.4) and UV detection at 280 nm. In this instance the signals from the UV detector were cross-correlated by multiplying a digitized reference chromatogram by the digitized analysis chromatogram and performing low pass filtering in the digital domain. The signal-to-noise ratio was improved by factors of 15 and 35 for I and II, respectively. Digital techniques are implemented to demonstrate the use of cross correlation to improve the signal-to-noise ratio for measurements involving analog detectors in flowing stream anal. methods. Two examples are presented. The first involves amperometric detection of dopamine using flow injection analysis. The reference and analyte signals are digitized and cross correlation performed by software using the fast Fourier transform (FFT). The second example is the determination of a mixture of catecholamines by HPLC using a UV detector. Multiplication of the digitize reference and analyte signals was carried out in the time domain followed by low pass filtering. Improvement in the signal-to-noise ratio up to a factor of 35 was found, depending on the compound
Dopamine Amperometry Cross correlation Signal to noise ratio Fourier transform Signal processing

"A Reticulated Vitreous Carbon Spectroelectrochemical Detector For Flow Injection Analysis And Liquid Chromatography"
Electroanalysis 1992 Volume 4, Issue 4 Pages 487-493
Janet Weiss Sorrels, Howard D. Dewald

Abstract: The design, construction and operation are described of a spectroelectrochemical detector, with a 1 cm optical path length, that incorporates an optically transparent reticular vitreous-carbon working electrode (cf. Dewald and Wang, Anal. Chim. Acta, 1984, 166, 163) which can easily be replaced in the event of electrode fouling. In the determination of [Fe(CN)6]3- by a flow injection procedure, with spectrophotometry at 410 nm, the calibration graph was rectilinear in the range 4 to 100 µM and the limit of detection was ~2 µM. Application of the detector in LC is exemplified by the analysis of a mixture of phenol, chlorophenols and nitrophenols. A spectroelectrochemical detector for flow injection and liquid chromatography is described. The detector design has dimensions of a standard 1 cm sample cuvette with a replaceable reticulated vitreous carbon working electrode. No special cell holder or modifications to the spectrophotometer are required to use the detector. Chronocoulometry is used to indicate a trend from thin-layer behavior toward semi-infinite diffusion behavior as the electrode pore size increases. Ferro-/ferricyanide solutions were used to evaluate the flow injection characteristics of the detector. A sampling rate of 180 injections per h was used. Linear calibration curves in the micromolar range were achieved with a reproducibility of 2-7%. A mixture of phenol, chlorophenols, and nitrophenols was used to investigate the simultaneous electrochemistry and optical response for liquid chromatography
Phenols Phenols, chloro Phenols, nitro Spectroelectrochemistry Electrode Apparatus Detector

"Electrocatalytic Oxidation And Flow Detection Of Hydrazine Compounds In Liquid Chromatography At A Vitamin B-12 Adsorbed Glassy Carbon Electrode"
Electroanalysis 1992 Volume 4, Issue 4 Pages 473-479
Jianxun Zhou, Erkang Wang*

Abstract: A vitamin B-12 chemically modified electrode (CME) was constructed by adsorption of vitamin B-12 onto a glassy carbon surface. The electrode catalyzes the electrooxidation of hydrazine compounds over a wide pH range. The electrocatalytic behavior of hydrazines is elucidated with respect to the CME preparation conditions, solution pH, operating potential, mobile phase flow rate, and other variables. When applied to liquid chromatographic detection of the analytes, the vitamin B-12 CME yielded a linear response range over 2 orders of magnitude, and detection limits at the picomole level. The vitamin B-12 CME offers acceptable catalytic stability in both batch and flow systems.

"A Solid Polymer Electrolyte Amperometric Detector For FIA And HPLC With Mobile Phases Of Low Conductivity"
Electroanalysis 1992 Volume 4, Issue 4 Pages 447-451
Luk&aacute;s Loub, Frantisek Opekar, Vera Pac&aacute;kov&aacute;, Karel Stul&iacute;k

Abstract: The design, construction and operation are described of a flow-through amperometric cell with a small Pt-wire working electrode and sub µL geometric volume and wherein the counter, working and reference electrodes are electrolytically connected by means of a Nafion solid polymer electrolyte. The cell was tested in a flow injection system with use of quinolin-8-ol (I), 4-methylcatechol (II) and K4Fe(CN)6 as model analytes. Calibration graphs were rectilinear from 0.2 to 0.6 µM up to 100 µM. In the determination of I at the 10 and 100 µM levels the coefficient of variation were 4.3 and 1.1% respectively (n = 10). Electrode activity decreased by 10 to 15% during a day's use but this could be restored by cyclic polarization of the working electrode between +1.6 and -0.2 V (vs. Ag - AgCl) for 15 min at 50 mV s-1. The detector has been applied in the HPLC determination of I, catechol and II on a Separon SGX C-18 column (15 cm x 3 mm) with aqueous 4% dioxan as mobile phase. AB An amperometric cell with a small platinum wire working electrode, a submicroliter geometric volume, and a solid polymer electrolyte (Nafion) was constructed and tested. The cell permits sensitive and reliable detection even in mobile phases of negligible elec. conductivity, (e.g., distilled water or nonpolar organic solvents). The sensitivity is substantially higher than that attained with similar cells containing large-area working electrodes; typical limits of detection amt. to analyte concentrations. between 10^-7 and 10^-6 mol/L, corresponding to subnanogram amounts in common HPLC sample volumes The detector response exhibits satisfactory linearity, a linear dynamic range of at least three concentration. decades, and a good precision, with relative standard deviations of 1 to 5%. This cell substantially widens the possibilities of amperometric detection, permitting direct application, for example, to normal-phase HPLC or to methods with programmed composition of the mobile phase (gradient elution).
8-Quinolinol 4-Methylcatechol Ferricyanide Amperometry Electrode HPLC Apparatus Linear dynamic range

"Photoelectrochemical Detection Of Alcohols"
Electroanalysis 1992 Volume 4, Issue 4 Pages 439-445
Joseph N. Barisci, Gordon G. Wallace

Abstract: The proposed method is based on the reaction of the analyte with a photo-sensitized quinone (e.g. benzoquinone or anthraquinone) in aqueous acetonitrile, followed by the amperometric determination of the product hydroquinone at a vitreous-carbon electrode. In a flow injection procedure, the sample was injected into aqueous 80% acetonitrile containing 80 mM NaClO4 and 10 ppm benzoquinone (flow rate 0.5 mL min-1) and amperometry was performed at an applied potential of 0.70 V vs. Ag - AgCl. Calibration graphs were rectilinear for up to 300 ppm of aliphatic alcohols up to C4 and limits of detection were ~2 ppm. Limits of detection could be improved by ~50% by use of pulsed amperometric detection. Results for ethanol in two beers and a sample of vodka were in good agreement with those obtained by GC - FID. The proposed technique has also been applied in the determination of alcohols by HPLC on a reversed-phase C18 column with aqueous 50% acetonitrile containing 50 mM NaClO4 and 10 ppm benzoquinone as mobile phase.
Alcohols Beer Vodka Amperometry Electrode Method comparison

"Voltammetry In Static And Flowing Solutions With A Large-amplitude Sine Wave Potential"
Electroanalysis 1992 Volume 4, Issue 4 Pages 429-437
John T. Long, Stephen G. Weber *

Abstract: Voltammetric detection is a potentially powerful method of detection for high performance liquid chromatography and flow injection analysis. A problem that needs a solution is its inferior detection limit compared to that obtained with amperometric detection. The shape of the potential waveform has been investigated in the search for methods of improving the detection limit of voltammetric detection. As a result, large amplitude sine wave potential perturbations have been found to give improved signal-to-noise ratios when compared to the values found for a corresponding triangle waveform (by a factor of from 1.1 to 5). This is principally due to the fact that the background current from a large amplitude triangle perturbation is spread over a wider frequency region. Signal processing techniques such as digital filtering have also been investigated. Digital bandpass filtering can be used to improve the signal to noise ratio by a factor of 2-13. Qualitative information (e.g., half-wave potential) is obtained through observing the phase angle at harmonics of the fundamental frequency.

"Column Liquid Chromatography In Combination With Immobilized Enzymes And Electrochemical Detection And Its Applications In Some Industrial Processes"
Electroanalysis 1992 Volume 4, Issue 4 Pages 403-427
Gy&ouml;rgy A. Marko-Varga

Abstract: A review, with 206 references. The first part of the paper provides a review of the pre- and post-column derivatization systems used in column liquid chromatography (CLC) in combination with immobilized enzyme reactors (IMERs) and electrochemical detection (EC). In the second part, an outline of important factors to consider in the optimization of CLC-IMER-EC systems are presented. Three industrial applications are described utilizing enzyme-based detection or enzymes for sample handling purposes. In two of the cases, CLC-IMER were used in combination with amperometric detection using chemical modified electrodes (CME). These applications were performed in the author's lab., and the high selectivity and sensitivity of these systems as well as the problems encountered in these complex samples will be discussed.
Fermentation broth Industrial HPLC Electrochemical analysis Review Post-column derivatization Pre-column derivatization Immobilized enzyme Optimization

"Identification Of Photochemical Products Of Amino-acids, Peptides, And Proteins In Online, Post-column Photolytic Derivatization Detection By HPLC - Electrochemistry"
Electroanalysis 1992 Volume 4, Issue 4 Pages 381-391
Lin Dou, Ira S. Krull

Abstract: In order to facilitate the online electrochemical detection of aromatic amino acids, peptides and proteins in HPLC, a post-column photolytic derivatization technique was developed (cf. Anal. Chem., 1990, 62, 2599) to convert non-electroactive compounds into electroactive derivatives. Further experiments have been carried out on model compounds (e.g. phenylalanine, tyrosine, cystine, tyrosine-glycine, phenylalanine-glycine, insulin and ribonuclease A) in order to understand the detection mechanisms. Photolysis was carried out offline and the decomposition products were identified mainly by HPLC. Photolytic processes that occurred in proteins included disulfide bond cleavage, photolysis of side-chain amino acids, and conformational changes. In most instances the electrochemical activity of proteins can be improved by photolysis thereby providing a means of improving the electrochemical detection of such compounds.
Amino Acids Peptides Proteins Phenylalanine Tyrosine Cystine Insulin Enzyme, ribonuclease a HPLC Electrochemical analysis Post-column derivatization Photochemistry

"Pulsed Electrochemical Detection At Noble Metal Electrodes In Liquid Chromatography"
Electroanalysis 1992 Volume 4, Issue 4 Pages 367-380
Dennis C. Johnson, William R. LaCourse

Abstract: The direct electrochemical detection of numerous polar aliphatic compounds is achieved at Au and Pt electrodes under the control of multistep potential-time waveforms. In this technique, called Pulsed Electrochemical Detection (PED), the waveforms manage the sequential processes of sampling the faradaic signal, from the oxidation of analyte, followed by oxidative cleaning and reductive reactivation of the electrode surfaces. The response mechanisms in PED are strongly influenced by surface properties of the electrodes and, therefore, members of each chemical classification detected are observed to produce virtually identical voltammetric response. Consequently, applications of PED have their greatest analytical significance when coupled with Liquid Chromatography (LC) to achieve a priori resolution of complex mixtures. The basic concepts of PED are reviewed and LC-PED results are presented for a variety of samples containing mixtures of alcohols, carbohydrates, alkanolamines, amines, and sulfur compounds.
HPIC Amperometry Electrode

"Removal Of Oxygen In Flowing Solutions Using A Photochemical Process"
Electroanalysis 1992 Volume 4, Issue 3 Pages 323-326
Joseph N. Barisci, Gordon G. Wallace

Abstract: The online deoxygenation of solution in flow systems by the photochemical reaction of O with an organic acid, e.g., formic, citric, oxalic, tartaric or acetic acid, in the flowing solution is described. Citric acid was the best O scavenger and proved more efficient than conventional purging with N gas. The method was applied in the detection of Cu, Cd and Pb, by flow injection anodic-stripping voltammetry.
Copper Cadmium Lead Voltammetry Interferences Photochemistry

"Catalytic Polarographic Detection Of Disulfides Following Liquid Chromatography"
Electroanalysis 1992 Volume 4, Issue 2 Pages 245-247
Kunio Nagashima, Minori Kamaya, Eizen Ishii

Abstract: A flow-through cell is described for use in both flow injection analysis and HPLC. The carrier solution was 0.2 M NH4OH - NH4Cl buffer (pH 9.5) - 0.5% methanol - 0.5 mM CoCl2, and analysis by HPLC was on a column (25 cm x 4.6 mm) of C18 with a mobile phase similar to the carrier, but with 0.5 mM Na trichloroacetate instead of CoCl2; this system could separate several disulfides. The detection cell contained a dropping-Hg working electrode, a Pt auxiliary electrode and SCE. Differential-pulse polarography of four compounds showed that the catalytic (Brdicka) currents occurred at peak potentials from -1.5 to -1.65 V. With use of 10 µL samples, the detection limit in HPLC was 0.1 mM of dithiodiacetic acid.
Disulfides Dithiodiacetic acid HPLC Polarography Electrode Flowcell

"Liquid Chromatography - Amperometric Detection Of Catechol, Resorcinol, And Hydroquinone With A Copper-based Chemically Modified Electrode"
Electroanalysis 1992 Volume 4, Issue 2 Pages 183-189
Jianxun Zhou, Erkang Wang

Abstract: Directions are given for the preparation of a vitreous-C electrode coated with crystalline CuCl, which was used in the detection cell as the working electrode, together with an Ag - AgCl reference electrode and a Pt counter electrode. The detector was used for both flow injection analysis and HPLC, in both instances with a 10 µL injection of the sample and with 0.05 M phosphate buffer (pH 7) containing 5% of methanol and 25 mM EDTA as carrier or mobile phase. The HPLC was carried out on a column (20 cm x 4 mm) of Nucleosil C18 (7 µm). Reproducible cathodic current peaks were obtained for all three phenols at +0.1 V. However, at other potentials, anodic currents were observed; the potential used could be chosen to give either positive or negative peaks (assisting identification) or peaks of negligibly small height (eliminating interference). At +0.1 V, calibration graphs were rectilinear for 2 to 1000, 5 to 600 and 5 to 800 ng injected for quinol, resorcinol and catechol, respectively, with corresponding detection limits of 1, 3 and 2 ng.
Catechol Resorcinol Hydroquinone Electrode Electrode Electrode Amperometry Interferences

"Automated System For Online Adsorptive Stripping Voltammetric Monitoring Of Trace Levels Of Uranium"
Electroanalysis 1992 Volume 4, Issue 2 Pages 161-165
Joseph Wang, Rossi Setiadji, Liang Chen, Jianmin Lu, Stephen G. Morton

Abstract: An automated system for online monitoring of trace U, based on a flow-through adsorptive stripping operation, is described. The online formation of the U-oxine complex is followed by its adsorptive accumulation and voltammetric quantitation at the downstream working electrode. About 10^-60 runs can be made every hour, with high reproducibility (relative standard deviation (RSD) of 3-5%) and a detection limit of 0.7 µg/L. The dependence of the peak current on different experimental variables is reported. The sequence of events involved in the adsorptive stripping voltammetric cycle is controlled by a computer. Analogous online monitoring of Cr(VI) is also reported, with 36 runs/h (2.1% RSD) and a detection
Uranium Chromium(VI) Voltammetry Process monitoring 8-Hydroxyquinoline Complexation

"Blank Response At Glassy-carbon Electrodes In A Flow Injection System"
Electroanalysis 1992 Volume 4, Issue 1 Pages 33-40
Yan Xu, H. Brian Halsall, William R. Heineman

Abstract: Factors influencing the blank response at a vitreous-carbon electrode were investigated with use of a BAS CC-4 amperometric thin-layer cell equipped with an Ag - AgCl reference electrode, a stainless-steel auxiliary electrode, and dual vitreous-carbon working electrodes operating in parallel. The blank response consisted of a transient component and a steady-state component. The transient response is attributed to non-faradaic current and faradaic current from the oxidation or reduction of electroactive surface groups on the vitreous carbon. The magnitude of the transient response depended on the applied potential, the temp., and the I and pH values of the sample solution, but was independent of flow rate. Rectilinear relationships were found between the transient response and the difference in I or pH between the injected sample and the carrier solution To keep the transient response 38 nC cm-2 the difference in I or pH must be controlled to within 0.01 M or 0.04, respectively. A complicated transient response that occurred at high positive potentials when the differential pH was high is attributed to changes on the vitreous-carbon surface.
Electrode Amperometry Optimization

"Determination Of Amalgam-forming Metals By Anodic-stripping Voltammetry In Solutions Containing Dissolved Oxygen"
Electroanalysis 1991 Volume 3, Issue 9 Pages 925-928
Miloslav Kopanica, Vera Stara

Abstract: Graphite powder (1 g) was mixed with silica gel (0.1 g) and the blend was further mixed with ceresin wax at 60°C. The warm mixture was pressed into a PTFE cylinder (5 cm x 0.2 mm) to form an electrode. Such electrodes (with Ag - AgCl reference and Pt counter electrodes) were used for linear scan or differential-pulse voltammetry. The solution for anlaysis were prepared to contain 0.1 M acetate buffer (pH 4.5) and 1 mM Hg(NO3)2 (to form the Hg film). After each use, the Hg film was removed mechanically or electrochemically. No O removal was necessary. Rectilinear calibration graphs were obtained for 5 to 150 µM of Cu(II), Pb(II) and Zn(II) with deposition at -1.2 V for 10 s (unstirred). For 10 to 500 nM solution of, e.g., Pb(II), the supporting electrolyte was 0.3 M HCl, the Hg2+ concentration. was 10 µM and deposition was for 3 min at -0.9 V, with stirring. The film was removed at +0.5 V. At 10 to 50 nM, the deposition was increased to 6 min. The method was applied in the determination of Pb in used motor oil (after extraction with 3 M HCl).
Metals Lead Oil Electrode Voltammetry Sample preparation Buffer Extraction Heated reaction Silica gel

"Potentiometric Anion Selectivities Of Polymer Membranes Doped With Indium(III) Porphyrins"
Electroanalysis 1991 Volume 3, Issue 9 Pages 909-916
S. B. Park, W. Matuszewski, M. E. Meyerhoff, Y. H. Liu, K. M. Kadish

Abstract: The cited membranes were prepared to contain 33% PVC, 66% o-nitrophenyl octyl ether and 1% of, e.g., chloro(octaethylporphyrinato)indium(III). Discs of the membrane were cut and placed in ion-selective electrode bodies, with an internal filling of 0.1 M KCl. Potentials were measured vs. Ag - AgCl. The response to 10 µm to 500 mM solution of 7 anions was measured and selectivity coefficient were calculated. The electrode showed enhanced and partly selective response to Cl-; the calibration graph was rectilinear for 1 to 500 mM Cl-. The electrode was applied in the flow injection determination of Cl- in serum (details given). The results obtained compared well with those obtained by the Ektachem analyzer..
Chlorine Blood Serum Electrode Potentiometry

"Electroanalysis With Electrodes Modified By Inorganic Films"
Electroanalysis 1991 Volume 3, Issue 9 Pages 869-878
James A. Cox, Robert Jaworski, Pawel J. Kulesz

Abstract: The electroanalytical utility of electrodes modified with inorganic films is reviewed. Various types of inorganic layers (metal oxides, polynuclear transition metal cyanides, zeolites, metal porphyrins and phthalocyanines) are assessed. Various detection schemes based on these modified surfaces are described in 129 references.
Amperometry Electrochemical analysis Electrode Electrode Electrode Electrode

"Determination Of Sulfur Dioxide In White Wines By Flow Injection With Electrochemical Detection"
Electroanalysis 1991 Volume 3, Issue 8 Pages 859-863
Terence J. Cardwell, Robert W. Cattrall, Chen Guo Nan, Peter J. Iles, Ian C. Hamilton, Geoffrey R. Scollary

Abstract: Wine samples were injected directly without pre-treatment into a carrier stream of 0.01 M H2SO4 (2.0 mL min-1). Sample solution were cleaned up by pre-electrolysis in a stainless-steel tube packed with graphite felt before amperometric detection of SO2 at +1 V vs. Ag - AgCl. Ascorbic and gallic acids were completely oxidized at +0.8 V thus eliminating interference. The concentration. of free SO2 was derived from a calibration plot. Total SO2 was measured by adjusting the pH of the sample to 12 with 0.5 M NaOH followed by dilution. The calibration graph was rectilinear up to 60 mg L-1 of SO2. Results agreed with those by the standard aspiration - oxidation method.
Sulfur dioxide Wine White Amperometry Electrochemical analysis Interferences pH

"An XPS Investigation Of Silver Bromide-coated Ion-selective Electrodes"
Electroanalysis 1991 Volume 3, Issue 8 Pages 815-822
C. A. Strydom, J. F. Van Staden, H. J. Strydom

Abstract: XPS data of AgBr-coated ion-selective electrodes exposed to high concentrations of Ag+, Cl-, Br-, I-, and NH3 revealed a change in the surface properties of the original electrode. A 40 min to one week exposure of the silver bromide ion-selective electrode surface to solutions containing high concentrations of chloride ions leads to the formation of a mixed halide layer, as the chloride ions are incorporated in the surface. Exposure to high concentrations of iodide-containing solutions results in a new silver iodide layer on top of the original silver bromide laver. Silver ions diffuse to the newly formed layers. NH3 results in the rapid degradation of the AgBr surface as the diamine complex, Ag(NH3)+2, is formed.
Electrode

"Batch Injection Analysis With The Rotating Disk Electrode"
Electroanalysis 1991 Volume 3, Issue 8 Pages 773-776
Liang Chen, Joseph Wang *, Lucio Angnes

Abstract: The use of the rotating disk electrode (RDE) for batch injection analysis (BIA) is illustrated. The technique involves injections of microliter samples into a large-volume blank solution, at a fixed location below the disk center. Transient response peaks - similar to those of flow injection analysis - are observed, reflecting the transport of the sample plug toward and away from the RDE. The effects of various experimental variables on the BIA/RDE operation are described. Injection rates of several thousand samples per hour can be achieved, with relative standard deviations of 1-3%, and detection limits at the micromolar (ng) level.
Electrode Batch injection analysis

"Adsorptive Stripping Voltammetry Of Cobalt And Nickel In Flow Systems At Wall-jet Electrodes"
Electroanalysis 1991 Volume 3, Issue 7 Pages 683-689
Christopher M. A. Brett*, Ana Maria C. F. Oliveira Brett, Jorge L. C. Pereira

Abstract: Adsorptive stripping voltammetry of cobalt and nickel in flow systems at wall-jet mercury thin-film electrodes has been investigated and assessed. A HEPES biological buffer with sodium perchlorate electrolyte was employed with excess nioxime, or dimethylglyoxime, ligand, and the accumulated complex on the mercury film surface determined by differential pulse reduction. Concentrations down to 1 nM can be routinely measured. Results at the wall-jet electrode, supported by evidence from LSV and impedance measurements at rotating and stationary electrodes respectively, show the viability of the method.

"Enzymic Determination Of Ethanol By Flow Injection Analysis Using A Kel-F Wax - Carbon-paste Electrode"
Electroanalysis 1991 Volume 3, Issue 7 Pages 625-630
Julie Wangsa, Neil D. Danielson

Abstract: The electrode was prepared from graphite powder and Kel-F wax in the wt. ratio 1.25:1. The graphite powder was first treated with hexane folowed by CHCl3, acetone and 6 M HNO3 and then dried at 100°C. This pre-treatment improved the reponse of the Kel-F wax - carbon-paste electrode by ~36% and improved electrode-to-electrode reproducibility. The graphite powder was added slowly with stirring to the melted Kel-F. After cooling and further mixing, a small amount of the paste was packed into the flow cell cavity, and the electrode surface was flattened and polished. The freshly prepared electrode was equilibrated for ~8 h by flow injection in the presence of buffer. Generally, the carrier solution used for standards and samples contained 20 iu mL-1 of alcohol dehydrogenase, 1.25 mM NAD+ and 2% (w/v) of polyoxyethylene glycol (to stabilize the enzyme) in 0.05 M Tris - HCl buffer (pH 8.0). Wine samples were diluted by a factor of 200 before analysis. The calibration graph was rectilinear from the detection limit of 0.44 mM to 33 mM.
Ethanol Wine Electrode Buffer Graphite Heated reaction Enzyme

"Tensammetric And Indirect Amperometric Detection Of Phospholipids"
Electroanalysis 1991 Volume 3, Issue 6 Pages 543-551
Thomas Schmidt, Hendrik Emons

Abstract: The adsorption characteristics of phospholipids at the hanging-Hg-drop electrode (HMDE) were studied in acetonitrile - water - methanol solution Tensammetric flow injection detection at the HMDE was also studied systematically with different experimental parameters. The results were applied to the HPLC determination of phospholipids on a Separon SGX 5 (5 µm) column with acetonitrile - water - methanol (39:7:4) containing 0.05 M LiClO4 as the mobile phase and tensammetric detection at -1.8 V. The detection limits were 1.5 µg for strongly adsorbed compounds and 4 to 5 µg for other phospholipids. In addition, an indirect amperometric flow injection detection system was examined, based on the inhibition effect of adsorbed phospholipids on electrode reactions of quinol at vitreous-carbon-fiber electrodes. The detection limits were in the range 1.0 to 9.5 µg.
Phospholipids Amperometry HPLC Electrode Electrode Sensor Indirect

"Amperometric Operation Of Porous Flow-through Electrodes At Very Low Conversion Efficiencies In Flow Stream Detectors"
Electroanalysis 1991 Volume 3, Issue 6 Pages 511-518
Caobin Zhu, David J. Curran

Abstract: The limiting current equation for a porous flow-through electrode operated amperometrically at low conversion efficiencies can be expressed in the same general format as that for amperometric detectors of other types. The equation shows that a critical dimension for the porous electrode is the pore diameter, the limiting current being inversely proportional to the two-thirds, power of the pore radius. Experimental verification was obtained using reticulated vitreous carbon (RVC) electrodes.
Amperometry LC Electrochemical analysis Electrode Electrode Electrode

"Highly Sensitive Determination Of L-lactate And Pyruvate By Liquid Chromatography And Amperometric Detection With Lactate Oxidase [lactate 2-monooxygenase] - L-lactate Dehydrogenase-co-immobilized Reactor Involving Amplification By Substrate Recycling"
Electroanalysis 1991 Volume 3, Issue 6 Pages 493-497
Toshio Yao, Naokazu Kobayashi, Tamotsu Wasa

Abstract: Pyruvate (I) and L-lactate (II) were determined in 10 µL of sample solution by flow injection reversed-phase HPLC on a column (25 cm x 4.6 mm) of ODS-T with 0.02 M phosphate buffer (pH 2.5) as mobile phase (0.4 mL min-1). Post-column reaction was carried out with 0.2 M phosphate buffer (pH 7.3) containing 0.5 mM NADH (0.25 mL min-1). The eluate was passed to the cited co-immobilized enzyme reactor where the I and II were recycled enzymatically to produce a large amount of H2O2. This was detected amperometrically at 0 V vs. Ag - AgCl by using a flow-through peroxidase electrode and mixing with 0.1 M phosphate buffer (pH 7.3) containing 0.5 mM K4Fe(CN)6 as mediator, pumped at 0.5 mL min-1. The detection limit was 0.02 pmol and the calibration graphs were rectilinear in the range 0.2 to 200 pmol for both I and II. The coefficient of variation was ~3.8% for 2 pmol of I or II (n = 5).
l-Lactate Pyruvate Amperometry HPLC Electrode Buffer Column Immobilized enzyme Reactor Sensitivity Reagent recycling

"Amperometric Glucose Sensor Using Silicon Oxide Deposited Gold Electrodes"
Electroanalysis 1991 Volume 3, Issue 6 Pages 469-475
Kenji Yokoyama, Eiichi Tamiya, Isao Karube

Abstract: SiO film was vapor-deposited onto Au electrodes shaped as bands of width 200 µm or discs of diameter 1 mm; glucose oxidase (GOD) was immobilized after activation of the SiO with alkylaminosilane reagent (aminopropyltriethoxysilane APTES or 3-aminopropyldimethylethoxysilane APDMES, 5% in toluene) followed by glutaraldehyde (2.5% in phosphate buffer, pH 7.4). In a flow injection system, a band electrode with APTES gave linear response to glucose in the range 1-200 mM. The behavior of disc electrodes with APDMES was studied using electron transfer mediators; SiO thickness 400 nm gave better response than 217 or 807 nm.
Glucose Amperometry Electrode Sensor

"Flow Injection Stripping Analysis"
Electroanalysis 1991 Volume 3, Issue 6 Pages 457-467
M. D. De LuqueCastro, A. Izquierdo

Abstract: A review is presented, with 58 references, of voltammetric and potentiometric stripping associated with flow injection analysis (FIA). The versatility and flexibility of FIA manifolds for performing unique stripping procedures are evaluated, and the instrumentation, features and applications of stripping methods in FIA are critically discussed.
Metals, heavy Biological Electrode Potentiometric stripping analysis Voltammetry Flow reversal Review

"Flow-through PH ISFET As Detector In Automated Determinations"
Electroanalysis 1991 Volume 3, Issue 4-5 Pages 349-354
S. Alegret, J. Bartrol&iacute;, C. Jim&eacute;nez, M. del Valle, C. Dom&iacute;nguez, E. Cabruja, A. Merlos

Abstract: A pH ISFET described previously (cf. Ibid., 1991, 3, 355) was installed in a specially designed flow-through cell (illustrated) and used together with a Ag - AgCl reference electrode in two different flow injection systems. The pH behavior of the sensor was tested by injecting sample into a pH 7 carrier buffer solution before mixing and measurement in the detection cell. The device exhibited near-Nernstian response from pH 3 to 11 and the calibration graph was rectilinear (r = 0.9975); the coefficient of variation was 1%. The device was applied in the determination of NH3 and SO2 with use of a gas diffusion unit with a polyvinylidene fluoride membrane. The pH of the carrier streams were modified with 1 M NaOH or 0.6 M HCl for determination of NH3 or SO2, respectively. Calibration graphs were rectilinear from 0.1 to 10 mM NH3 and 0.07 to 4 mM SO2 with corresponding coefficient of variation of ~1% and 0.5%.
pH Electrode Field effect transistor Automation Gas diffusion

"Amperometric Response Of Electrodes With Porous Coating To Gaussian Concentration Profiles In Flowing Streams"
Electroanalysis 1991 Volume 3, Issue 4-5 Pages 293-297
John Cassidy*, William Breen, Michael E. G. Lyons

Abstract: A numerical simulation is performed to calculate the amperometric response for a porous coating on an electrode surface to a Gaussian concentration plug in a flowing stream. The amperometric response is considered as a function of the layer thickness, the diffusion coefficient of the analyte through the layer, and the width of the Gaussian concentration profile. We consider the effect of the first two parameters on the magnitude of the current response and the lag time, which is the time delay between the time at which the peak of the concentration profile reaches the outer edge of the porous layer and the time of the peak current response. However, although it is not possible to decouple the magnitudes of the layer thickness and the diffusion coefficients from experimental measurements, it is possible to determine one parameter if the other is known. The width of the amperometric response varies linearly with that of the incident Gaussian concentration profile.

"Peroxidase-ferrocene Modified Carbon Paste Electrode As An Amperometric Sensor For The Hydrogen Peroxide Assay"
Electroanalysis 1991 Volume 3, Issue 4-5 Pages 281-285
Pilar Dom&iacute;nguez S&aacute;nchez, Arturo Jos&eacute; Miranda Ordieres, Agust&iacute;n Costa Garc&iacute;a, Paulino Tu&ntilde;&oacute;n Blanco *

Abstract: A new enzymatic amperometric sensor for hydrogen peroxide based on a modified carbon paste electrode is described. Horseradish peroxidase and ferrocene mediator were immobilized by dissolution or dispersion in a graphite-paraffin oil paste. To prevent losses of immobilized chemicals under operational conditions, the electrode surface was coated with a Nafion membrane. The device exhibits a relatively fast response time (42 s for 95% of the steady-state response) and yields currents linearly related to the hydrogen peroxide concentration over the 10^-7 to 10^-5 mol/L range in both static and flow injection operations. The slope of the calibration plot remained constant for more than 20 days. Flow injection assays of hydrogen peroxide at a sampling rate of about 70 injections per hour, with a relative standard deviation of 1.4%, are possible. An easy and low cost preparation procedure is described.

"Signal Shapes And Single-boundary Measurements In Flow Injection Analysis With Amperometric Detection"
Electroanalysis 1991 Volume 3, Issue 4-5 Pages 273-280
Arnold G. Fogg, Rui Zhao

Abstract: Studies were carried out on the shapes of analytical signals in normal and reverse flow injection schemes with use of single channel manifolds, amperometric and spectrophotometric detection and small and large (>1.5 ml) injection volumes. Contributions to the final signal from dispersion at the front and rear boundaries of the injected bolus often appear to be unequal. With loop injection, the rear boundary travels further than the leading boundary and is dispersed more, although injection by stream switching eliminates this factor. With spectrophotometric detection, correction for large and opposite refractive index effects at the two boundaries may be required. In amperometric detection, differences in acidity between the carrier stream and sample can cause significant changes in background current on switching leading to signal distortion at low concentration. When these factors are eliminated, other factors causing peak height and peak shape differences are still present, e.g. differences in dispersion rates of reactants and reaction rates.
Amperometry Spectrophotometry Dispersion Refractive index Reverse Peak shape

"Flow Injection Determination Of Methionine With Amperometric Detection At A Stable Modified Electrode"
Electroanalysis 1991 Volume 3, Issue 3 Pages 239-242
James A. Cox, Ewa Dabek-Zlotorzynska

Abstract: A vitreous-carbon electrode was polished with alumina, rinsed in an ultrasonic bath and modified by cycling in 2 mM RuCl3 - 2 mM K4Ru(CN)6 - 0.5 M KCl medium (adjusted to pH 2 with HCl) between 500 and 1100 mV vs. Ag - AgCl at 50 mV s-1 for 40 cycles. The cell was filled with carrier solution and stored on open circuit when not in use. The electrode catalyzed the oxidation of methionine at 0.92 V vs. Ag - AgCl. A rectilinear calibration graph was obtained for flow injection amperometry over the range 0.6 to 180 µM with 0.2 M K2SO4 as carrier at pH 2, a 7.5 µL sample volume, and a flow rate of 1 mL min-1. The sensitivity was 0.05 µM nA-1 at a 0.07-cm2 electrode. After a single surface preparation, the sensitivity remained constant over >3 weeks with daily use.
Methionine Amperometry Electrode Catalysis pH

"Electrocatalysis And Flow Detection At A Glassy-carbon Electrode Modified With A Thin Film Of Oxymanganese Species"
Electroanalysis 1991 Volume 3, Issue 3 Pages 215-219
Ziad Taha, Joseph Wang

Abstract: A vitreous-carbon electrode was modified by cycling the potential between -0.5 and +0.4 V vs. Ag - AgCl in 27 mM MnCl2 - 1.4 M NaOH medium. The electrode was shown to reduce greatly the overvoltage for the oxidation of hydrazine, methylhydrazine or H2O2, thereby facilitating amperometric detection of these compounds in flowing streams. Effects of pH, flow rate, operating potential, film thickness, concentration. and other variables on the catalytic response of the electrode were studied; the response was very stable. Detection limits at the fmol and pmol levels and coefficient of variation of 1.3% in flow injection analysis are reported.
Amperometry Electrode Electrode Electrode Catalysis Flow rate measurement pH

"Flow Injection Analysis Of Myoglobin And Haemoglobin At A Toluidine Blue [C. I. Basic Blue 17] Chemically Modified Electrode"
Electroanalysis 1991 Volume 3, Issue 3 Pages 203-207
Jianxun Zhou, Erkang Wang

Abstract: A polished vitreous-carbon working electrode was cycled between -0.40 and +1.3 V vs. Ag - AgCl at 100 mV s-1 for 1 min in 1 M H2SO4, and was subsequently maintained at -0.40 V vs. Ag - AgCl for 30 s in the mediator solution of 50 µM-toluidine blue in 1 M H2SO4. For flow injection analysis (FIA), a freshly polished vitreous-carbon working electrode placed in the top half of the thin-layer flow-cell assembly so that only the flat end of the electrode was in contact with the solution When the modified electrode was used a detector for FIA at a constant applied potential of -0.30 V vs. SCE, it gave detection limits of 20 and 50 ng (1.2 and 0.78 pmol) injected of myoglobin and haemoglobin, respectively, with a dynamic rectilinear concentration. range of two orders of magnitude. After a brief equilibration period, the electrode retained nearly 90% of its initial myoglobin response over 8 h of continuous exposure in the flow-through system.
Hemoglobin Myoglobin Electrode Electrode Potentiometry

"An XPS Investigation Of The Influence Of Bromide And Iodide Solutions On The Surface Of Silver Chloride Coated Ion-selective Electrodes"
Electroanalysis 1991 Volume 3, Issue 3 Pages 197-202
C. A. Strydom, J. F. van Staden, H. J. Strydom

Abstract: X-Ray photoelectron spectroscopic (XPS) data of AgCl-coated, ion-selective electrodes exposed to solutions containing high concentrations of bromide and iodide ions revealed that the surface properties of the original electrode changed. The mixed phases, AgBrsCl1-s and AgIsCl1-s, seem to form initially on the electrode surface, with the existence of the AgICl phase much shorter than that of the AgBrCl phase. This indicates that the formation of the Agl surface layer is kinetically faster than the formation of the AgBr layer. In both cases XPS data showed the ultimate formation of AgBr and AgI layers on top of the original AgCl-coated, ion-selective electrode surface after being subjected to solutions containing either bromide or iodide ions. The conversion of the crystalline-coated, chloride-selective electrode surfaces to AgBr and AgI layers, however, transformed the chloride-selective electrodes into bromide- or iodide-selective electrodes with electrode properties different from those of the original electrode.
Electrode Interferences Apparatus

"Electrocatalytic Amperometric Detection At Polymeric Cobalt Phthalocyanine Electrodes"
Electroanalysis 1991 Volume 3, Issue 2 Pages 119-124
Xiaohe Qi, Richard P. Baldwin, Huawen Li, Thomas F. Guarr

Abstract: The cited chemically modified electrodes were prepared according to the method of Li and Guarr (cf. J. Chem. Soc., Chem. Commun., 1989, 832) with polymeric surface coverage from 1 to 10 nmol cm-2. The electrode was applied to the detection of thiol compounds under flow injection conditions with use of a Ag - AgCl reference electrode (pH 3.2), an applied potential of +0.55 V and an aqueous mobile phase containing 50% of methanol or acetonitrile. In most cases, response was rectilinear over 2 to 3 orders of magnitude of concentration. with detection limits from 0.1 pmol for N-acetylcysteine to 5 pmol for 6-mercaptopurine. The electrodes are extremely stable and can be readily adapted for HPLC conditions.
Thiols Amperometry HPLC Electrode Electrode Catalysis

"Amperometric Glucose Electrode Based On Carbon Paste, Chemically Modified With Glucose Dehydrogenase, Nicotinamide-adenine Dinucleotide And A Phenoxazine Mediator, Coated With A Poly(estersulfonic Acid) Cation Exchanger"
Electroanalysis 1991 Volume 3, Issue 2 Pages 77-86
Gudrun Bremle, Bj&ouml;rn Persson, Lo Gorton

Abstract: Four different mixtures of enzyme and cofactor carbon pastes were prepared (details given) and analyzed for glucose response and stability. Best results were obtained with electrodes consisting of 100 mg of C, 40 µL of paraffin oil, 3.7 mg of meldola blue, 8 mg of glucose dehydrogenase (GDH) and 51.7 mg of NAD+ coated (x6) with the polymer membrane. The preferred electrode was evaluated in a flow injection analysis system (50 µL samples). The calibration graph was rectilinear from 0.1 to 20 mM glucose at 100 mV vs. Ag - AgCl. The sample throughput was 40 h-1 and results compared well with those obtained by sensors based on GDH immobilized on solid graphite electrodes.
Glucose Amperometry Electrode Enzyme

"A New Approach To Coulometry For Flow-through Systems"
Electroanalysis 1991 Volume 3, Issue 1 Pages 49-51
L. Y. Bao, Z. W. Tian

Abstract: A new method of flow-through coulometry is presented. The fundamental principle is different from that in the conventional method. Two working electrodes are involved in the coulometric cell. An electrolysis efficiency of only 20 to 30% is required for the measurement. From the response coulombs (Q1 and Q2) of the two working electrodes, the charge (Qc) calculated by using Equation 4 correspond to an electrolysis efficiency of 100% and is independent of the temperature and flow rate.
LC Coulometry Detector

"Electrocatalysis And Flow Detection Of Alcohols At Ruthenium Dioxide-modified Electrodes"
Electroanalysis 1991 Volume 3, Issue 1 Pages 37-42
Donal Leech, Joseph Wang, Malcolm R. Smyth

Abstract: Potentiostatic (+0.4 V) experiments were carried out with a AgCl - AgCl reference electrode, a Pt wire auxiliary electrode with a RuO2 chemically modified working electrode and NaOH electrolyte solution Amperometric detection was used in both batch and flow injection systems by using convective mass transport of 600 rpm and 0.5 mL min-1, respectively. Detection limits were 16 µM, 45 µM, 1.2 mM and 2.4 mM for glycerol, ethylene glycol, methanol and ethanol, respectively, in the flow injection system. The electrode markedly decreases the overpotentials for alcohol oxidation and offers increased stability over enzymatic sensors for ethanol.
Alcohols Amperometry Electrode Electrode Catalysis

"Use Of Chemically Modified Electrodes For Liquid Chromatography And Flow Injection Analysis"
Electroanalysis 1991 Volume 3, Issue 1 Pages 1-11
Erkang Wang, Huamin Ji, Weiying Hou

Abstract: The use of chemically modified electrodes (CMEs) for liquid chromatography and flow-injection analysis is reviewed. Electrochemical detection with CMEs based on electrocatalsis, permselectivity, ion flow in redox films, and ion transfer across the water-solidified nitrobenzene interface is discussed in terms of improving the stability, selectivity, and scope of electrochemical detectors and the detection of electroinactive substances. More than 90 references are included.
LC Electrode Catalysis Column Review Selectivity

"Determination Of The Dissociation Potentials Of Metal-complexes By Computerized Flow Injection Potentiometric Stripping Analysis"
Electroanalysis 1990 Volume 2, Issue 8 Pages 631-636
Manar Fayyad

Abstract: A method is described for determining the dissociation potentials of metal complexes using computerized flow-injection potentiometric stripping analysis (CFIPSA). The dissociation potentials of Bi:NTA and Bi:EDTA complexes are determined at pH 2 by measuring the bismuth(III) concentrations (i.e., the counts in solutions containing the 1:1 complexes at different deposition potentials between -0.15 and -0.90 V vs. Ag/AgCl). Dissociation potentials of -0.35 and -0.50 V vs. Ag/AgCl have been found for Bi:NTA and Bi:EDTA, respectively.
Metals Potentiometric stripping analysis Computer Complexation

"Elimination Of Interferences In Flow Injection Amperometric Determination Of Glucose In Blood Serum Using Immobilized Glucose Oxidase"
Electroanalysis 1990 Volume 2, Issue 8 Pages 607-616
Wojciech Matuszewski, Marek Trojanowicz*, Andrzej Lewenstam

Abstract: A flow-injection system with anodic amperometric detection for glucose determination in human blood serum samples was optimized by a comparison of various arrangements of enzyme immobilization and the elimination of interferences. The best results were obtained using a compact membrane biosensor in a wall-jet, flow-through detector with a platinum disk electrode covered with an evaporated Nafion layer, a polyester membrane with immobilized glucose oxidase, and another protective polyester membrane. In the optimized conditions, a linear response was observed up to 25 mM glucose with a detection limit of 200 M glucose and a sampling rate of 120 samples/h for a 20 µL sample volume. Results of glucose determination in human serurn were compared with a Beckman Glucose Analyzer 2 and a Kone Dynamic analyzer.
Glucose Blood Serum Amperometry Sensor Interferences Immobilized enzyme

"Amperometric Flow Injection Analysis Of L-glutamate Using An Immobilized-enzyme Reactor: Amplification By Substrate Recycling"
Electroanalysis 1990 Volume 2, Issue 7 Pages 563-565
Toshio Yao*, Naokazu Kobayashi, Tamotsu Wasa

Abstract: A column (5 mm x 4 mm i.d.) of LiChrosorb NH2 (10 µm) was activated by circulation of 5% glutaraldehyde solution in 0.05 M NaHCO3 for 1.5 h, then washed with 0.1 M phosphate buffer of pH 7.0 before co-loading with glutamate oxidase (8.5 iu) and alanine aminotransferase (118 iu) by circulation of the enzyme solution in the same buffer for 2 h at room temperature The resulting reactor was washed for 3 h with 0.1 M glycine buffer of pH 7.5, and was stored in the 0.1 M phosphate buffer at 5°C when not in use. The reactor was positioned between the injector and a Yanagimoto flow-through Pt electrode in the flow injection system described previously (Anal. Chim. Acta, 1990, 231, 121) for the determination of L-glutamate with use of 1 mM L-alanine in 0.1 M phosphate buffer (pH 7.2) as carrier solution and an applied potential of 0.5 V vs. Ag - AgCl. The reaction principle is described. At the optimum reactor temperature of 37°C and a flow rate of 0.3 mL min-1, the amplification factor was 24; the detection limit was 0.1 µM and the calibration graph was curvilinear. The method could also be used to determine 2-oxoglutarate.
l-Glutamate Amperometry Electrode Electrode Immobilized enzyme Column Buffer pH Injector Detection limit Calibration Heated reaction

"FIA Analysis With Immobilized Oxidase/peroxidase Enzymes And Fluoride Electrode Detection"
Electroanalysis 1990 Volume 2, Issue 7 Pages 525-531
Wojciech Matuszewski, Marek Trojanowicz*, Mark E. Meyerhoff

Abstract: Details are given of flow injection manifold arrangements in which (a) glucose oxidase (I) and horse-radish peroxidase (II) are co-immobilized on nylon net or a polyester membrane, which is then mounted on a F--selective electrode; (b) the two enzymes are immobilized on controlled-pore glass beads in a single reactor preceding the electrode; or (c) I is immobilized on glass beads in a reactor following the sample injection valve in the carrier stream, and II is so immobilized in a reactor following the merge point of the carrier and reagent streams and preceding the electrode. The sample is a substance that is enzymatically (by I) oxidized to yield H2O2, and the H2O2 then reacts with a fluoriaromatic compound as reagent, catalyzed by II, to liberate F- for detection. Arrangements (b) and (c) showed greater catalytic efficiency and better sensitivity than arrangement (a); glucose could be determined at 0.1 to 10 mM at throughputs of >30 h-1 by using arrangement (b). Either 4-fluorianiline or pentafluoriphenol (5 mM) in acetate buffer of pH 5.5 could be used as reagent; incorporation of 10 or 20 µM-NaF in the reagent stream stabilized the baseline potential. The F- electrode was more selective then amperometric detection systems for H2O2.
Hydrogen peroxide Electrode Amperometry Immobilized enzyme Nylon Membrane Controlled pore glass Glass beads Valve Catalysis Enzyme pH Buffer

"Pineapple-tissue-based Bio-electrode For The Determination Of Hydrogen Peroxide"
Electroanalysis 1990 Volume 2, Issue 7 Pages 511-515
Meng Shan Lin, Sock Ying Tham, Garry A. Rechnitz*

Abstract: Ground pineapple core tissue (60 mg) was mixed with 0.94 g of carbon paste [graphite powder - mineral oil (11:9)] and the mixture was packed into an electrode body. The electrode was installed in a flow cell having a channel 0.127 mm deep (volume 15 µL), and its potential (vs. a Ag - AgCl micro-electrode) was controlled by a BAS model CV-1B cyclic voltammograph (Bioanalytical Systems, West Lafayette, IN) and monitored by a Keithley 169 multimeter (Keithley Instruments, Cleveland, OH). The assembly was applied for the determination of H2O2 by flow injection analysis with a carrier solution of 0.1 M phosphate buffer (pH 7.4) containing 1 mM o-phenylenediamine as H donor. The flow rate was 1.1 mL min-1 and the electrode potential was -200 mV. Response was sufficiently rapid to allow a sampling rate of >60 h-1 at 1 mM H2O2 and the detection limit was 2.1 µM. Catechol, dopa, dopamine, tryptophan and tyrosine (0.1 mM) interfered by causing 35% suppression of the current response for 0.2 mM H2O2 in the presence of o-phenylenediamine. The electrode response remained stable for 20 days.
Hydrogen peroxide Electrode Enzyme Flowcell Buffer Detection limit Interferences

"Determination Of The Pesticide Guthion By Flow Injection Analysis With Amperometric Detection"
Electroanalysis 1990 Volume 2, Issue 6 Pages 487-492
J. Hern&aacute;ndez M&eacute;ndez, R. Carabias Mart&iacute;nez*, E. Rodr&iacute;guez Gonzalo, J. P&eacute;rez Trancon

Abstract: Guthion, a pesticide, was determined by flow injection analysis using single- and three-channel systems with and without a chemical reaction. The experimental variables involved in each case were investigated and optimized, and the analytical features of the two procedures were compared. A method based on the oxidation of anthranilic acid yielded in the alkaline hydrolysis of the pesticide at a glassy carbon electrode is proposed for its determination. The detection limit is 4.1 times 10^-7 M, and the relative standard deviation is 2.2% (n = 10) when the hydrolysis reaction takes place within the three-enamel manifold. The method is based upon the oxidation at a vitreous-carbon electrode of anthranilic acid (I) produced in the alkaline hydrolysis of the cited pesticide (II). A methanolic solution of I is injected (157 µL) into a 0.06 M acetic acid - 0.04 M Na acetate - 20% methanol carrier stream that is subsequently mixed with 0.4 M NaOH and passed through a 2-m reaction coil. Then 0.5 M acetic acid is added to the reaction mixture and the resulting solution is passed through a 49-cm tubular reactor and into the detector cell where I is determined amperometrically at +1.2 V (vs a Ag - AgCl electrode) at a wall-jet vitreous-carbon electrode. The calibration graph is rectilinear for 96.6 µM-II and the detection limit is 0.41 µM. At 38.6 µM the coefficient of variation was 2.2% (n = 10). By carrying out hydrolysis separately and using a single channel flow injection system the limit of detection is reduced to 18 nM-II. In this instance the calibration graph was rectilinear for 28.0 µM-II and for 0.84 µM-(II) the coefficient of variation was 2.5% (n = 10).
Pesticides Guthion Amperometry Electrode Electrode Optimization Redox Detector Detection limit Calibration

"Dynamic Response Characteristics Of An Impinging-jet Amperometric Detector"
Electroanalysis 1990 Volume 2, Issue 6 Pages 463-469
Francis E. Powell, Arnold G. Fogg*

Abstract: By use of [Fe(CN)6]4- as test species an investigation was carried out to determine the dynamic response characteristics of the impinging-jet electrode described previously [cf Fogg and Summan, Analyst (London), 1984, 109, 1029]. Laminar flow from a straight delivery tube was modified by mixing stages in the electrode channel and its connections. The effective detection volume was ~7 µL and therefore the detector would not be expected to contribute significantly to overall dispersion in practical flow injection systems.
Iron(2+) hexacyanide Amperometry Electrode Laminar flow Straight tube Detector Dispersion Apparatus

"Instrument For Alternating-current Voltammetry Featuring A Digital Phase-sensitive Detector - Application To Flow Injection Analysis Using AC Amperometry"
Electroanalysis 1990 Volume 2, Issue 6 Pages 435-442
David J. Curran*, Mark B. Gelbert, Edward D. Kingsley

Abstract: The design, construction and operation are described of an instrument for a.c. electrochemical measurements on solution containing low concentration. of analyte. The unit incorporates a lock-in amplifier based on a digital phase-sensitive detector. The phase angle resolution and signal capture ratios were better than 0.01°C and as high as 80,000, respectively. Application of the instrument is demonstrated in the determination of 6 nM-o-dianisidine by flow injection a.c. amperometry.
1,2-Dianisidine Amperometry Voltammetry Detector Apparatus

"Flow Injection Analysis Of Hydrogen Peroxide Using A Horseradish Peroxidase-modified Electrode Detection System"
Electroanalysis 1990 Volume 2, Issue 4 Pages 303-308
Pilar Dominguez S&aacute;nchez, Paulino Tu&ntilde;&oacute;n Blanco, Jos&eacute; Maria Fern&aacute;ndez Alvarez, Malcolm R. Smyth*, Richard O'Kennedy

Abstract: Horse-radish peroxidase was adsorbed on to a vitreous-carbon electrode, which was then used in a flow injection system for determination of H2O2. Sample solution (20 ml) was injected into a stream (10 mL min-1) of deoxygenated 0.1 M phosphate buffer (pH 7.0) containing 0.1 mM quinol, and the quinone produced was detected at -0.30 V vs. Ag - AgCl. The calibration graph was rectilinear for 25 nM to 1 µM-H2O2, and the detection limit was 10 nM. The coefficient of variation (n = 7) was 1.3% for 0.3 µM. Possible interference was studied.
Hydrogen peroxide Electrode Electrode Buffer Detection limit Interferences

"Experimental-study Of Phase-sensitive AC Voltammetry In Continuous-flow Streams - Reversible Systems"
Electroanalysis 1990 Volume 2, Issue 4 Pages 273-278
Edward D. Kingsley, David J. Curran*

Abstract: Fundamental harmonic a.c. voltammetry at flow-by wall electrodes is independent of flow rate from 0 to 2.1 L min-1, and the shape of the a.c. voltammogram is also not influenced by flow rate. An equation is presented to describe quantitatively the a.c voltammogram for a reversible, electron-transfer reaction. The conclusions cannot be extrapolated to other types of electrode reactions.
Voltammetry

"Evaluation Of Electrodes Coated With Metal Hexacyanoferrate As Amperometric Sensors For Nonelectroactive Cations In Flow Systems"
Electroanalysis 1990 Volume 2, Issue 4 Pages 263-272
Karsten N. Thomsen, Richard P. Baldwin*

Abstract: Two electrodes modified with either nickel or cupric hexacyanoferrate films were evaluated and compared as sensors for nonelectroactive cations in a flow injection system. Both gave responses for group 1A and ammonium ions, but only the electrode modified with cupric hexacyanoferrate was sufficiently stable for use in flowing solutions. This electrode responded to K+, NH-4+, Rb+, and Cs+ ions rather selectively. Within this group, the selectivity could be controlled from general to almost specific toward Cs+ by the potential at which the electrode was poised. The electrode was compatible with a mobile phase of dilute nitric acid commonly used in ion chromatography, and chromatographic detection limits of 2 times 10^-7 M and linear responses over two decades were obtained. The electrode was applied to the ion chromatographic analysis of K+ and NH-4+ in urine and K+ in blood serum samples.
Potassium Ammonium Rubidium Cesium Blood Serum Urine Amperometry Sensor HPIC

"Characterization Of Poly(estersulfonic Acid)-coated Micro-voltammetric Electrodes"
Electroanalysis 1990 Volume 2, Issue 3 Pages 253-256
Joseph Wang*, Meng Shan Lin

Abstract: The micro-electrode was fabricated by coating a glass micro-pipette packed with Dylon graphite paste with a poly(estersulfonic acid) film (details given). The electrode was characterized by voltammetry vs. Ag - AgCl and a Pt auxiliary electrode under flow injection conditions. The attractive permselective, ion-exchange, antifouling and dynamic properties of the polyester ionomer together with its low cost and strong adherence to surfaces could be very valuable for in vivo brain electrochemistry, and offers an effective alternative to Nafion coatings.
Electrode Voltammetry Ion exchange Glass Graphite Low cost Nafion membrane

"Glassy Carbon Microband Electrochemical Detector For High-performance Liquid Chromatography"
Electroanalysis 1990 Volume 2, Issue 3 Pages 209-215
Javad M. Zadeii, Rosalind Mitchell, Theodore Kuwana

Abstract: An elecrochemical microband thin-layer flow cell that incorporates a thin glassy carbon electrode was fabricated and tested. The microband, tested with ferrocyanide and catecholamine oxidation, exhibited properties of a microelectrode with excellent electroactivity and signal-to-noise (S/N) response. For the chromatographic determination of several catecholamines at the 100 fmol level, the relative standard deviation as measured by the peak height ranged from 3-8%. The detection limit for DOPAC was 5 fmol (S/N = 3). The microband thin-layer cell gives an improved S/N ratio at an applied potential of 0.6 V vs. Ag/AgCl compared to that of a conventionally sized glassy carbon electrode. The small surface area of the microband allows rapid stabilization of chromatographic background (baseline) following the application of the potential. The microband thin-layer flow cell has a volume of 5 L and exhibits a flow-rate-independent response, reduced ohmic drop, and gradient elution capability. The microband cell has great potential for commercialization as a universal detector for liquid chromatography.

"Simultaneous Enzymatic Determination Of Glucose And Ascorbic Acid Using Flow Injection Amperometry"
Electroanalysis 1990 Volume 2, Issue 2 Pages 147-154
Wojciech Matuszewski, Marek Trojanowicz *, Liliana Ilcheva

Abstract: Sample solution (10 µL) is injected into a carrier stream of water (2 mL min-1) that subsequently merges with a stream of phosphate buffer solution The mixed stream then divides into two; one passes directly to the amperometric detector, whilst the other passes through a reactor containing glucose oxidase immobilized on controlled-pore glass and then through a delay coil before passing to the detector. The resulting signal consists of two peaks, the first corresponding to oxidation of ascorbic acid (I) and the second to the oxidation of I and enzymatically produced H2O2. Results for synthetic mixtures of I and glucose (up to 20 and 100 mM, respectively) agreed well with expected values. Recoveries of I and glucose added to fresh citrus juice were 100 to 101.8% and 100 to 102.5%, respectively. The sampling rate is 20 h-1
Glucose Ascorbic acid Amperometry Enzyme Buffer Detector Controlled pore glass

"Precise Analysis Of Silver By Flow Injection Analysis With Stripping Voltammetric Detection"
Electroanalysis 1990 Volume 2, Issue 2 Pages 133-137
Li Qun Zhang, Peter E. Sturrock*

Abstract: Sample solution was introduced into a carrier stream of 0.1 M Al(NO3)3 - 2 mM HNO3 by timed partial-loop injection from a 2 mL sample loop under computer control, and the solution passed into a wall-jet cell equipped with a Pt-disc working electrode, an annular Pt counter electrode concentric with the inlet jet, and an Ag - AgCl reference electrode, the salt bridge of which was concentric with the working electrode. After deposition at 0 V for 30 to 60 s, stripping was carried out by application of either a square-wave or staircase sweep between +0.1 and +0.7 V. The calibration graph was rectilinear for 80 nM to 40 µM-Ag+, and the coefficient of variation ranged from 0.12 to 0.78%. There was no interference from 4 µM-Cd, -Cu, -Fe, -Pb or -V. The method was developed as an indirect means of determining the current efficiencies of Hall cells on a short-term basis.
Silver Voltammetry Electrode Computer Calibration Interferences

"Flow-reversal Injection Analysis For Improved Stripping Voltammetry"
Electroanalysis 1990 Volume 2, Issue 2 Pages 127-132
Joseph Wang *, Huang Huiliang, Wladyslaw Kubiak

Abstract: Repeated reversal of the flow direction during deposition in flow injection stripping voltammetry promotes improved plating efficiency and hence better detection limits. In the determination of Pb2+ at a Hg-coated carbon-fiber electrode, a 13-fold enhancement in response was obtained by application of 10 flow oscillations, which corresponded to a detection limit of 7 nM as compared with 90 nM with a once-through system. The calibration graph (15 oscillations) was rectilinear in the range 0.1 to 0.8 µM-Pb (injection volume 0.1 ml); at 0.5 µM (10 oscillations) the coefficient of variation (n = 10) was 6%. The better plating efficiency also permits use of smaller sample volume.
Lead(2+) Voltammetry Electrode Detection limit Calibration Flow reversal

"Flow Injection Amperometry Of Cysteine And Glutathione At An Electrode Modified With A Ruthenium-containing Inorganic Film"
Electroanalysis 1990 Volume 2, Issue 2 Pages 107-112
James A. Cox *, Thomas J. Gray

Abstract: A vitreous-carbon electrode modified with a thin film of Ru oxides (prep. described) promotes the diffusion-controlled oxidation of cysteine and glutathione at +0.92 V (vs. Ag - AgCl). In flow injection amperometry in 0.2 or 0.02 M K2SO4 (pH 2.0), log. - log. calibration graphs were rectilinear over three orders of magnitude, and detection limits (injection volume 7.5 µL) were 1 µM. Up to 60 samples h-1 could be analyzed, and there was no evidence of electrode fouling during use. The electrode exhibited no change in sensitivity after regular use during 2 weeks.
Cysteine Glutathione Amperometry Electrode Diffusion Calibration Detection limit Sensitivity

"Conductivity Monitoring By An Amperometric Detector With A Cu(II)-containing Poly(3-methylthiophene) Electrode"
Electroanalysis 1990 Volume 2, Issue 1 Pages 1-7
Zhi-Lun Xue, A Ersin Karag&ouml;zler, O. Yavuz Ataman, Ahmed Galal, Adel Amer, R. Shabana, Hans Zimmer, Harry B. Mark Jr. *

Abstract: A conducting, chemically synthesized, Cu(II)-containing poly(3-methylthiophene) powder was pressed into a pellet and used as the working electrode of a three-electrode system in a thin-layer amperometric cell unit to detect ionic analytes in an aqueous stream by flow-injection analysis. The electrode response was linearly correlated with the applied voltage, which was varied between 0.2 and 3.0 V (vs. Ag/AgCl). It was shown that the electrode possesses favorable sensitivity and stability in comparison with other metallic electrodes such as stainless steel and Pt. During a period of more than a year, it showed no deterioration in its performance.

"Electrocatalysis And Determination Of Hydrazine Compounds At Glass-carbon Electrodes Coated With Mixed-valent Ruthenium(III,II) Cyanide Films"
Electroanalysis 1989 Volume 1, Issue 6 Pages 517-521
Joseph Wang*, Ziling Lu

Abstract: Chemically modified electrodes were prepared by anodizing vitreous-carbon electrodes in a RuCl3 - K4Ru(CN)6 solution Such electrodes catalyse the oxidation of hydrazines in acidic and neutral media, and show improved stability and a broader pH range of application then previous phthalocyanine surfaces. The response of hydrazine, methylhydrazine and dimethylhydrazine were evaluated with respect to film preparation conditions, pH, potential scan rate, concentration. and other variables. The electrodes were used in a flow injection system. The calibration graph was rectilinear for 5 to 50 µM-hydrazine, and the detection limit was 0.2 µM. The coefficient of variation was 1.3% (n = 30).
Methylhydrazine Dimethylhydrazine Electrode Electrode Optimization Catalysis

"Manganese(III) - Porphyrin-based Thiocyanate-selective Membrane Electrodes: Characterization And Application In Flow Injection Determination Of Thiocyanate In Saliva"
Electroanalysis 1989 Volume 1, Issue 6 Pages 477-484
D. V. Brown, N. A. Chaniotakis, I. H. Lee, S. C. Ma, S. B. Park, M. E. Meyerhoff*, R. J. Nick, J. T. Groves

Abstract: The electrode membrane comprised 1% of 5,10,15,20-tetrakis-(2,4,6-triphenyl)porphyrinatomanganese(III) chloride, 66% of dibutylsebacate and 33% of PVC; the internal buffer solution contained 50 mM 2-morpholinoethanesulfonic acid - 10 mM NaCl (adjusted to pH 5.5 with 1 M NaOH), and also contained 50 µM NaSCN. The electrode responds preferentially to SCN- over inorganic (e.g., ClO4-, Cl- and Br-) and organic (e.g., ascorbate, citrate and urate) ions often present in biological samples. Whereas the selectivity of the electrode for SCN- was different in a non-equilibrium flow system compared with that under equilibrium conditions, its response allowed determination of SCN- in saliva by flow injection analysis. The carrier stream was the cited buffer (without addition of NaSCN). From 0.01 to 1 mM SCN- could be determined. Results showed good agreement with those of a colorimetric method.
Thiocyanate ion Saliva Electrode Electrode Method comparison

"An Electrical Sensor For Hydrogen Peroxide Based On Peroxidase Adsorbed On A Spectrographic Graphite Electrode"
Electroanalysis 1989 Volume 1, Issue 5 Pages 465-468
G. J&ouml;nsson, L. Gorton*

Abstract: Horseradish peroxidase was found to strongly adsorb on the surface of spectrographic graphite with retained catalytic activity. Efficient electron transfer from the graphite to the oxidized form of adsorbed peroxidase could be achieved without the deliberate addition of a mediator. The peroxidase-modified graphite was used as a sensor for hydrogen peroxide in a flow injection system. Response currents to hydrogen peroxide start at +600 mV vs. SCE and reach a maximal value at -200 mV. Highest activities were found between pH 4 and 6. Linear calibration curves for hydrogen peroxide were obtained from 0.1 to 500 µM with an injection volume of 50 µL.
Hydrogen peroxide Electrode Electrode Sensor

"Mediated Enzyme/wall-jet Amperometric Electrode In Flow Injection Monitoring Of Glucose"
Electroanalysis 1989 Volume 1, Issue 5 Pages 423-429
Hari Gunasingham *, Chin-Huat Tan

Abstract: Tetrathiafulvalene serves as a useful mediator for glucose oxidase in its application in second-generation enzyme electrodes for monitoring glucose. Among its useful characteristics are a low redox potential, fast homogeneous electron exchange kinetics with glucose oxidase, high stability, and low solubility in aqueous solutions. The fabrication and characterization of tetrathiafulvalene-glucose oxidase enzyme electrodes in flow-injected and stopped-flow analysis is described. One of the conclusions is that the homogeneous rate constant for tetrathiafulvalene is higher than that of dimethyl ferrocene. Tetrathiafulvalene is, however, more susceptible to pH variations. The characteristics and advantages of the mediated enzyme/wall-jet amperometric detection are described.
Glucose Electrode Electrode Amperometry

"Amperometric Determination Of Lactose In Human And Cow's Milk Using A Flow Injection System With Some Immobilized Enzyme Reactors"
Electroanalysis 1989 Volume 1, Issue 4 Pages 413-416
Toshio Yao*, Reina Akasaka, Tamotsu Wasa

Abstract: A bioelectrochemical flow-injection system is proposed for the determination of lactose in milk from humans and cows. The system includes an amperometric flow-through platinum electrode to measure hydrogen peroxide, which was enzymatically generated by injecting a 10-L sample into the packed-bed reactors of immobilized -galactosidase and glucose oxidase that are incorporated in series in the flow line. Because the presence of glucose interfered with the measurement of lactose, a precolumn packed with coimmobilized glucose oxidase and catalase was positioned just before the two immobilized enzyme reactors to remove the glucose from the milk. The peak current was linearly related to the lactose concentration between 0.01 and 2.0 mM. The determinations of lactose in milk could be performed at a rate of 60 samples/h with satisfactory precision (less than 0.8% RSD) and no pretreatment except for the sample dilution.
Lactose Milk Cows Milk Amperometry Reactor Injection technique Immobilized enzyme

"Pretreatment Of Glassy Carbon Electrodes By Anodic Galvanostatic Pulses With A Large Amplitude"
Electroanalysis 1989 Volume 1, Issue 5 Pages 405-412
J&uuml;rgen Mattusch, Karl-Heinz Hallmeier, Karel Stul&iacute;k*, Vra Pac&aacute;kov&aacute;

Abstract: Glassy carbon electrodes (GCEs) can be activated by the passage of large-amplitude (for example, 20-mA) anodic galvanostatic pulses with durations shorter than 1 second. The increased activity stems from an increase in the rate of charge-transfer reactions and from the adsorption accumulation of the analytes on the electrode surface, which is demonstrated for catecholamines and ascorbic acid. As demonstrated by X-ray photoelectron and fast-atom-bombardment mass spectrometry, the galvanostatic treatment leads to an increase in the amount of chemisorbed oxygen. Scanning electron microscopy shows very small mechanical changes of the electrode surface. The activation effect depends on the composition of the test solution and the character of the analytes. There is an optimal electric charge that produces the highest electrode activity and lowers the limits of determination for catecholamines by approximately two orders of magnitude; on further increase in the charge, the electrode activity decreases (due to the formation of a thick layer of graphite oxide). The activation effects are less pronounced in flow-through measurements. The method can be readily implemented for the periodic, automated reactivation of glassy carbon electrodes, but the optimal conditions must be found experimentally for various systems.

"Use Of Mercury Drop Electrodes For Polarographic Measurements In Flowing Solutions"
Electroanalysis 1989 Volume 1, Issue 5 Pages 379-388
Wladyslaw W. Kubiak

Abstract: The use of dropping mercury, hanging mercury drop, and static mercury drop electrodes in flow analysis and liquid chromatography is reviewed. Theoretical considerations (particularly flow rate dependence), measuring techniques, designs of flow-through detectors, and methods of oxygen removal in flow systems are discussed. A brief guide to flow applications of mercury electrodes is also given.

"Stabilization Of A Ruthenium Polymer-modified Electrode For Use In Flowing Solution Analysis"
Electroanalysis 1989 Volume 1, Issue 4 Pages 357-361
G. G. Wallace*, M. Meaney, M. R. Smyth, J. G. Vos

Abstract: Various methods have been investigated to stabilize a ruthenium polymer-modified electrode for use in flow-injection analysis. These include treatment with ultraviolet irradiation as well as coating the modified electrode with electrochemically generated conductive and nonconductive polymer layers. The stabilization procedures tested proved effective in improving the operational half-life of a nonstabilized electrode from 8 hours to more than 48 hours for the determination of test analyte species such as nitrite and nickel bis-2-hydroxyethyl dithiocarbamate.
Electrode Electrode

"An Ultraviolet-cured, PH-sensitive Membrane Electrode For Use In Flow Injection Analysis"
Electroanalysis 1989 Volume 1, Issue 4 Pages 353-356
Florian R. del Mundo, Terence J. Cardwell, Robert W. Cattrall*, Peter J. Iles, Ian C. Hamilton

Abstract: The preparation of an epoxyacrylate, UV-cured polymer membrane electrode for determining pH is described. This is based on the neutral carrier, tridodecylamine, and shows Nernstian behavior from pH 5 to 10. Interferences from cations in this range are negligible. The response of the electrode is very fast, reaching more than 90% of the equilibrium value in less than 1 second, which makes it very suitable for use in flow injection analysis (FIA). The application of the electrode to the determination of pH in flow injection analysis using a miniature flow cell is described, and the influence of the buffer capacity and pH of the carrier on the accuracy of the pH measurement is discussed. The FIA system has been applied to the determination of the acidity of some soil samples.
Electrode Electrode

"Evaluation Of Flow-through Photochemical Reactors For Liquid Chromatography With Electrochemical Detection"
Electroanalysis 1989 Volume 1, Issue 4 Pages 347-351
Jose N. Barisci, Gordon G. Wallace*

Abstract: A method which allows evaluation of the irradiation efficiency of flow-through photoelectrochemical detector cells for liquid chromatography and flow injection analysis has been developed. The method is based on the determination of the light intensity incident inside of the irradiation cell using the potassium ferrioxalate actinometer. The concentration of the actinometer is measured electrochemically in the flowing system. Typical detector cells used for photoelectrochemical detection were evaluated to demonstrate the method.

"Rapid Coulometry With A Porous Carbon Felt Electrode Using Iodide Or Ferrocyanide Ion Mediators"
Electroanalysis 1989 Volume 1, Issue 4 Pages 323-326
Shunichi Uchiyama*, Shuichi Suzuki, Osamu Hamamoto

Abstract: The oxidizing agents of iodide and ferrocyanide ions, such as 1,4-benzoquinone and the iodate ion have been determined by rapid (9-25 seconds) coulometry. The electrolytic solution is confined to the pores of the carbon felt electrode and the sample is added to the carbon felt surface, which is maintained at a fixed potential. Current efficiencies approached 100% for sample concentrations ranging from 1 x 10^-5 to 1 x 10^-1 M with relative standard deviation of 0.6-2.2%. The determination of residual chlorine in drinking water has been carried out using the same coulometric cell, and the results obtained by the present method are in good agreement with those obtained by the orthotolidine method.
Coulometry Electrode Electrode

"The Use Of Chemisorbed Electrocatalytic Polymers For Detection In Flowing Solutions"
Electroanalysis 1989 Volume 1, Issue 3 Pages 245-250
Jose N. Barisci, Gordon G. Wallace*, Ellen A. Wilke, Mary Meaney, Malcolm R. Smyth, Johannes G. Vos

Abstract: The use of a chemically modified electrode for amperometric detection in flowing solutions is described. The modifier is a ruthenium-containing polymer ([Ru(bpy)2(PVP)5Cl]Cl) that exhibits electro-catalytic properties. The polymer-coated electrodes are less prone to fouling (product adsorption) problems and show enhanced sensitivity for various dithiocarbamate metal complexes and nitrite ions. Limitations of the chemisorbed polymer coatings are discussed.

"Simultaneous Measurements Of Trace Metals By Adsorptive Stripping Voltammetry"
Electroanalysis 1989 Volume 1, Issue 3 Pages 229-234
Joseph Wang*, Jawad Mahmoud, Javad Zadeii

Abstract: Simultaneous measurements of trace metals, based on adsorptive stripping voltammetry of their chelates with dihydroxyazo dyes, are demonstrated. Variables affecting the resolution between neighboring chelate peaks, including the ligand and its concentration, pH, adsorption time and potential, concentration ratio, and scan rate, are assessed. Adequate resolution is demonstrated for more than 10 pairs of metals, present at the ppb level. Possible changes in peak heights, associated with competition for the complexing ligand and/or coadsorption effects, are explored. Different concentration ratios of the mixture components can be tolerated. Applicability to seawater analysis is illustrated.
Uranium Titanium Aluminum Iron Molybdenum Vanadium Thorium-232 Nickel Cobalt Manganese Copper Gallium Zinc Tin Water Voltammetry

"Glucose Enzyme Electrode Preparation By The Codeposition Of Platinum And Glucose Oxidase Onto Glassy Carbon"
Electroanalysis 1989 Volume 1, Issue 3 Pages 223-227
Hari Gunasingham*, Chee-Beng Tan

Abstract: A glucose enzyme electrode was fabricated by the simultaneous electrodeposition of enxyme and platinum particles onto a glassy carbon substrate. The electrode combines the electrocatalytic activity of platinum and the stability of glassy carbon. The application of the electrode in flow-injection detection of glucose is shown. A wide linear range and good precision is possible.
Platinum Enzyme, glucose oxidase Electrode Electrode Immobilized enzyme

"Pulsed Amperometric Detection Based On Direct And Indirect Anodic Reactions: A Review"
Electroanalysis 1989 Volume 1, Issue 3 Pages 189-197
Deborab S. Austin-Harrison, Dennis C. Johnson*

Abstract: Pulsed amperometric detection (PAD) is applicable for the quantitative detection of numerous organic compounds that adsorb at noble metal electrodes but cannot be detected satisfactorily by conventional amperometry at constant (dc) applied potential. A multistep waveform is applied in PAD with chrono-amperometric detection based on faradaic signals, which frequently are produced by surface-controlled reactions. We briefly review applications of PAD for liquid chromatography and present a unified explanation of the various modes of anodic response.

"Computerized Potentiometric Stripping Analysis Using Asyst Software: Application To Lead Determination In Wines And Vinegars"
Electroanalysis 1989 Volume 1, Issue 2 Pages 177-180
Saverio Mannino*, Giuseppe Fregapane, Mariagrazia Bianco

Abstract: A computerized system for potentiometric stripping analysis made of commercially available components with corresponding software is described. Application to the determination of lead in wines and vinegars is also reported.
Lead Wine Food Potentiometric stripping analysis Computer

"Electroanalytical Method For Estimation Of Fish Freshness Using A Flow Injection System With Some Immobilized Enzyme Reactors"
Electroanalysis 1989 Volume 1, Issue 2 Pages 173-176
Toshio Yao*, Yoshihiro Matsumoto

Abstract: The method involves determination of (a) hypoxanthine (I) plus inosine (II) and (b) the sum of I, II, IMP and AMP; the ratio of the two peak currents is used in calculating a freshness index. The two-channel flow injection system incorporates reactors containing (i) AMP deaminase, (ii) alkaline phosphatase, and (iii) purine-nucleoside phosphorylase - xanthine oxidase, respectively, immobilized on LiChrosorb NH2 (details given). These catalyse (i) conversion of AMP into IMP plus NH3, (ii) conversion of the endogenous and enzymatically formed IMP into II plus phosphate, and (iii) reaction of II with phosphate to form I and oxidation of I to uric acid plus H2O2. The H2O2 is detected with a peroxidase - bovine serum albumin membrane electrode. The carrier solution is 50 mM glycine buffer of pH 7.0 containing 3 mM MgCl2, and Fe(CN)64- is used as mediator in the indicator reaction. Fifteen samples can be analyzed in 1 h.
Hypoxanthine Inosine Marine Electrode Reactor Immobilized enzyme Buffer

"Carbon Paste Electrode Chemically Modified By Direct Admixing Of Tris-(4,7-diphenyl-1,10-phenanthroline)iron(II)"
Electroanalysis 1989 Volume 1, Issue 2 Pages 155-160
Christopher J. Hynes, Mojtaba Bonakdar, Horacio A. Mottola*

Abstract: The electrodes (radius 3 mm) were prepared by mixing tris-(4,7-diphenyl-1,10-phenanthroline)iron(II) perchlorate (I) with graphite and acetone and then adding light mineral oil. A typical paste contained 10% of I, 56% of graphite and 34% of oil. Cyclic voltammetry at the electrode with use of a BAS-100 electrochemical analyzer gave one stable Fe(III)-reduction peak at ~+1.0 V vs. Ag - AgCl and one oxidation peak at ~+1.2 V, which disappeared with successive cycling; both peaks were almost independent of pH in the range 1 to 5. The electrode (which has a low rate of loss of I by leaching) was applied in the determination of NO2 from its electrocatalytic oxidation of I in a continuous-flow system; typical coefficient of variation (n = 10) at 15 ppb (v/v) of NO2 in air were ~5%.
Nitrogen dioxide Environmental Electrode Electrode Voltammetry Apparatus Detector

"Flow Cell Based On Glucose Oxidase-modified Carbon-fibre Ultra-micro-electrode"
Electroanalysis 1989 Volume 1, Issue 2 Pages 151-154
Joseph Wang*, Ruiliang Li, Meng-Shan Lin

Abstract: Five 7 µm diameter carbon fibers were aspirated into the tip of a borosilicate-glass capillary tube (1.2 mm i.d.) and sealed with epoxy-resin; electrical contact was made by Hg and Cu wire. The electrode was modified by potentiostatic platinization (at -0.18 V vs. Ag - AgCl for 15 min) in 5 mL of solution containing hydrated H2PtCl6 (165 mg), glucose oxidase (7.5 mg) and Pb(NO3)2 (3 mg); the pH was adjusted to 3.5 with NaOH. After the co-deposition of glucose oxidase and Pt particles, the electrode was dipped for 1 h in 0.1 M phosphate buffer (pH 6.8) with stirring, and then inserted into one arm of a glass T-piece that formed the flow cell (constructional details given), with a PTFE tube as solution inlet in the other arm. The cell outlet was dipped into a downstream reservoir containing the reference and auxiliary (Pt wire) electrodes, and measurements were made 30 to 40 min after the working potential (+0.80 or +0.85 V) was applied. In flow injection analysis, the calibration graph for glucose was rectilinear from 0.1 to 1 mM, and the detection limit was 13 µM (230 ng in a 100 µL injection); the coefficient of variation (n = 40) was 3%. The electrode remained active over a 20-day period.
Glucose Electrode Electrode Electrode Flowcell Detector Apparatus

"Ion Transfer Across Water - Solidified Nitrobenzene Interface As Amperometric Flow Detector"
Electroanalysis 1989 Volume 1, Issue 1 Pages 75-80
Erkang Wang*, Huamin Ji

Abstract: A three-electrode thin-layer flow-through cell is described that incorporates nitrobenzene solidified by means of PVC and agar to act as the working electrode (area 7.07 mm2). The nitrobenzene phase contains also 50 mM tetrabutylammonium tetraphenylborate in order to make contact with a Ag - AgCl electrode (in aqueous solution solidified by agar containing 50 mM tetrabutylammonium chloride). Reference and auxiliary electrodes are positioned downstream of the working electrode. By using this detector, flow injection analysis was carried out to determine cations (choline, acetylcholine, tetramethylammonium, tetrabutylammonium and Cs+) and anions (ClO4-, IO4- and ReO4-). Calibration graphs were rectilinear over two orders of magnitude of concentration. (injection volume 20 µL), and detection limits ranged from 4 to 40 ng; coefficient of variation were 3.1% (n = 5, 7 or 12). The method was applied in detecting choline and acetylcholine separated on a C18 column.
Choline Acetylcholine Cesium Perchlorate Periodate Perrhenate HPLC Amperometry Electrode Apparatus Detector

"Potentiometric Selectivity Study Of Crown Ethers Containing Four Ring Oxygen Atoms And Benzoxymethyl Or Carboxylic Acid Side Chains As Ionophores For Lithium And Potassium"
Electroanalysis 1989 Volume 1, Issue 1 Pages 63-67
Abdulrahman S. Attiyat, Gary D. Christian*, Richard A. Bartsch

Abstract: Five crown ethers with four ring oxygen atoms and different types of pendant groups were used to prepare ion-selective electrodes by coating a membrane containing the crown ether on the tip of a silver wire incorporated in a flow cell. A flow injection analysis study was conducted to determine the potentiometric selectivities of the crown ethers for lithium, sodium, potassium, magnesium, and calcium ions. It was found that crown ethers with neutral side arms show selectivities for lithium over other ions, while those of acidic side arms show selectivities for potassium over the other ions. The effect of the addition of trioctylphosphine oxide to the electrode matrix was also investigated. A comparison is made between the potentiometric selectivities of the crown ethers for certain metal ions and their selectivities in extracting the ions into an organic phase.

"Horse-radish-root-modified Carbon Paste Bioelectrode"
Electroanalysis 1989 Volume 1, Issue 1 Pages 43-48
Joseph Wang*, Meng Shan Lin

Abstract: The crushed root (0.11 g) was hand-mixed with 0.9 g of mineral oil (Aldrich) and then with 1.1 g of graphite powder. A portion of the paste was packed into the electrode cavity of a thin-layer detector, and the amperometric response (at -0.2 V vs. Ag - AgCl) to H2O2 (due to peroxidase activity) was evaluated in flow injection and continuous-flow systems with use of phosphate buffer media (pH 7.4) containing 1 mM o-phenylenediamine. The calibration graph was rectilinear up to 0.12 mM H2O2, the detection limit was 0.3 µM and the coefficient of variation (n = 15) at 1 mM was 1.4%. Response time was short (down to 11 s); oxidizable biological compounds did not interfere, but the response to riboflavine was similar to that to water. The electrode was also applied to the determination of glucose (in the presence of glucose oxidase) with a rectilinear response up to 60 µM, a detection limit of ~1.6 µM and a coefficient of variation (n = 20) at 80 µM of 2.6%.
Glucose Hydrogen peroxide Sensor Electrode Apparatus Detector Buffer Interferences

"Evaluation Of Ultra-thin Ring And Band Micro-electrodes As Amperometric Sensors In Electrochemical Flow Cells"
Electroanalysis 1989 Volume 1, Issue 1 Pages 23-33
John W. Bixler*, Michael Fifield, Jordan C. Poler, Alan M. Bond, Wolfgang Thormann

Abstract: The electrodes (0.1 to 0.5 µm thick), on 2- or 4-mm borosilicate- or soda-glass rod, were produced by sputtering, by firing Pt or Au paint, or from Au foil, and were mounted in the working electrode port of a Metrohm EA1096 thick-layer wall-jet flow-through cell. An array of three vapor-deposited Au band electrodes (each 0.1 µm x 0.5 mm), mounted parallel to the flow direction in a thin-layer channel cell, was also constructed. These ultra-thin sensors, together with a jet-centred carbon micro-disc, were characterized by cyclic voltammetry, and were evaluated in the amperometric flow injection mode (vs. a non-aqueous Ag - Ag+ electode) for temporal stability, calibration sensitivity, background signal and flow rate dependence of the analytical signal by injection of ferrocene in acetonitrile containing 0.1 to 10 mM tetramethylammonium perchlorate. The detection limit of 3 to 6 nM obtained with Au-paint ring electrodes on borosilicate glass was an order of magnitude lower than that of any of the other electrodes tested, and analytical signals from the Au-paint and -foil rings, the band array and the carbon micro-disc had the best temporal stability.
Amperometry Voltammetry Electrode Electrode Sensor Flowcell Calibration Sensitivity