University of North Florida
Browse the Citations
-OR-

Contact Info

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

View Stuart Chalk's profile on LinkedIn

Derivatization

Classification: Chemical Process -> Derivatization

Citations 30

"A Simple Method For The Speciation Of Organotin Compounds In Water Samples Using Ethylation And GC-QFAAS"
Microchim. Acta 2001 Volume 136, Issue 3-4 Pages 137-141
Nikolaos S. Thomaidis, Freddy C. Adams, Themistokles D. Lekkas

Abstract: A simple method for the extraction of organotin compounds from water samples was developed in which both the instrumental parameters and the extraction/derivatization step were optimized. Organotin compounds (butyl-, phenyl- and octyl-) in tap water samples were ethylated with the addition of 2.5 mL of 0.4% w/v NaBEt4 at pH 5.00 and subsequently extracted two times, for 10 min, with 3 and 2 ml of hexane. The combined extracts were analyzed with on-column capillary GC-QFAAS. The recoveries were quantitative for di- and tri- alkyltin compounds, whereas between 67 and 86% of the monoalkyltin compounds were recovered. The detection limits obtained ranged from 110 pg for monobutyltin to 500 pg for triphenyltin, as sensitivities were found to be compound dependent. The preparation of ethylated standards was also optimized. It was found that two subsequent extractions, with 1.0 and 0.5 mi of hexane were necessary for the quantitative recovery of the ethylated organotin compounds.

"A Sensitive And Rapid Assay For 4-aminophenol In Paracetamol Drug And Tablet Formulation, By Flow Injection Analysis With Spectrophotometric Detection"
Talanta 2002 Volume 58, Issue 6 Pages 1301-1310
M. S. Bloomfield

Abstract: 4-Aminophenol (4AP) is the primary degradation product of paracetamol which is limited at a low level (50 ppm or 0.005% w/w) in the drug substance by the European, United States, British and German Pharmacopoeias, employing a manual colorimetric limit test. The 4AP limit is widened to 1000 ppm or 0.1% w/w for the tablet product monographs, which quote the use of a less sensitive automated HPLC method. The lower drug substance specification limit is applied to our products, (50 ppm, equivalent to 25 µg 4AP in a tablet containing 500 mg paracetamol) and the pharmacopoeial HPLC assay was not suitable at this low level due to matrix interference. For routine analysis a rapid, automated assay was required. This paper presents a highly sensitive, precise and automated method employing the technique of Flow Injection (FI) analysis to quantitatively assay low levels of this degradant. A solution of the drug substance, or an extract of the tablets, containing 4AP and paracetamol is injected into a solvent carrier stream and merged on-line with alkaline sodium nitroprusside reagent, to form a specific blue derivative which is detected spectrophotometrically at 710 nm. Standard HPLC equipment is used throughout. The procedure is fully quantitative and has been optimized for sensitivity and robustness using a multivariate experimental design (multi-level Central Composite response surface) model. The method has been fully validated and is linear down to 0.01 µg mL-1. The approach should be applicable to a range of paracetamol products. (C) 2002 Elsevier Science B.V. All rights reserved.

"Enhanced Chemiluminescent Determination Of Chloramphenicol And Related Nitro Compounds By On-line Photochemical Reaction"
Analyst 2000 Volume 125, Issue 7 Pages 1313-1319
V. David, R. M. Marín Sa&eagrave;z, J. V. García Mateo and J. Martínez Calatayud

Abstract: The viability of tandem photochemical reaction-chemiluminescence detection was studied for a heterogeneous family of nitro compounds using chloramphenicol as a test substance. The on-line chemical photodegradation of chloramphenicol was performed in a flow injection assembly by using a photoreactor consisting of a 725 cm x 0.5 mm id piece of PTFE tubing coiled around an 8 W low-pressure mercury lamp. Photodegraded chloramphenicol was detected by oxidizing photo-fragments from the parent compound and their subsequent reaction with a luminol-Co(II) system. The calibration graph was linear up to 3 x 10^-5 mol L-1 chloramphenicol, the limit of detection was 3 x 10^-9 mol L-1, the relative standard deviation was 1.8% for 2 x 10^-6 mol L-1 of the drug and the sample throughput was 60 h-1. The proposed method was used to determine chloramphenicol in pharmaceutical formulations and its application to other related nitro compounds was studied.

"Selective Flow Injection Biamperometric Determination Of Sulfur-containing Amino Acids And Structurally Related Compounds"
Anal. Chim. Acta 2001 Volume 438, Issue 1-2 Pages 281-289
M. Catalá Icardo, O. Armenta Estrela, M. Sajewicz, J. V. García Mateo and J. Martínez Calatayud

Abstract: A simple and selective flow injection method for the determination of cysteine and methionine is proposed. The method is based on the reaction of the amino acid with chloramine-T and the subsequent reaction of thr excess of chloramine-Tr with an acidic solution of iodide producing a stoichiometric amount of tri-iodide (diminution of the flow injection analysis (FIA) peak) which is determined biamperometrically using two platinum electrodes polarized at 100 mV. The calibration graph is linens up to 10 µg mL-1 of cysteine and 30 µg mL-1 of methioninc; the limit of detection is 0.06 and 0.1 µg mL-1: the repeatability (also as percent of a series of 70 continuous FIA peaks of 5 µg mL-1 of cysteine or 15 µg mL-1 of methionine) is 1.1 and 0.7 for cysteine and methionine, respectively. The sample throughput is 220 h-1 in both cases. A large study on the influence of foreign substances is performed especially focused on the rest of L-amino acids. The method is applied to the determination of cysteine, methionine and N-acetyl-cysteine, penicillamine and cystine as structurally related compounds in pharmaceutical and veterinary samples. Finally, the proteins methionine enkephalin and oxytocin are determined on the basis of their contents in both amino acids.

"Coupling Pervaporation To AAS For Inorganic And Organic Mercury Determination. A New Approach To Speciation Of Hg In Environmental Samples"
Fresenius J. Anal. Chem. 2001 Volume 371, Issue 8 Pages 1124-1129
Consuelo Fernandez-Rivas, Riansares Muñoz-Olivas, Carmen Camara

Abstract: The design and development of a new approach for Hg speciation in environmental samples is described in detail. This method, consisting of the coupling of pervaporation and atomic absorption spectrometry, is based on a membrane phenomenon that combines the evaporation of volatile analytes and their diffusion through a polymeric membrane. It is proposed here as an alternative to gas chromatography for speciation of inorganic and organic Hg compounds, as the latter compounds are volatile and can be separated by applying the principles mentioned above. The interest of this method lies in its easy handling, low cost, and rapidity for the analysis of liquid and solid samples. This method has been applied to Hg speciation in a compost sample provided by a waste water treatment plant.

"Electrochemical Analysis Of D-penicillamine Using A Boron-doped Diamond Thin Film Electrode Applied To Flow Injection System"
Talanta 2002 Volume 58, Issue 6 Pages 1213-1219
Nattakarn Wangfuengkanagul and Orawon Chailapakul

Abstract: The electroanalysis of D-penicillamine in 0.1 phosphate buffer (pH 7) was studied at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry as a function of concentration of analyte and pH of analyte solution. Comparison experiments were performing using a glassy carbon (GC) electrode. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, but the GC electrode provided only an ill-defined response. The BDD electrode provided a linear dynamic range from 0.5 to 10 mM and a detection limit of 25 muM (S/B : 3) in voltammetric measurement. It was also found that the peak potentials were decreased when the pH of the analyte solution was increased. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. The flow injection analysis results at the diamond electrode indicated a linear dynamic range from 0.5 to 50 muM and a detection limit of 10 nM (S/N approximate to 4). The proposed method was applied to determine D-penicillamine in dosage form (capsules), the results obtained in the recovery study (255±2.50 mg per tablet) were comparable to those labeled (250 mg per tablet). (C) 2002 Elsevier Science B.V. All rights reserved.

"Photochemical Reactivity Of Sulfamethoxazole And Other Sulfa Compounds With Photodiode Array Detection"
Microchem. J. 2002 Volume 72, Issue 2 Pages 147-154
Abdulqawi Numan, Jennifer L. Villemure, Krystal K. Lockett and Neil D. Danielson

Abstract: The photochemical activities of six sulfa compounds [sulfacetamide (CET), sulfadiazine (DIA), sulfaguanidine (GUA), sulfamerazine (MER), sulfamethoxazole (SMX), and sulfamethizole (MET)] under different experimental conditions such as photolysis time, solvent and buffer pH are investigated by photodiode array (PDA) spectrophotometry. With no photolysis, the sulfa drugs CET and DIA show no absorbance at 332 nm and the other compounds only modest absorbance. Upon photolysis for 4 min, absorbance enhancements at 332 nm of three to four times for GUA and MET and 12-15 times for SMX and MER are observed. For CET and DIA after photolysis, the (absorbance) 1/mg is now approximately 0.01-0.02 units. Although two pH optima of approximately 3-4 and 7 are noted, the optimum solvent for photolysis is ethanol without pH adjustment. For flow injection (171) with on-line photolysis and PDA detection, a mobile phase of 100% ethanol with a step flow rate from 0.1 to 1 ml/min is used providing a 4-min reaction time. The FI detection limit for SMX with photolysis at 330 nm is 1 mg/l. The relative standard deviation data (n=4) of seven individual points in a calibration curve from 5 to 150 mg/l are 0-4%. The recovery of SMX from pharmaceutical tablets is 99.7% indicating no interference from trimethoprim which is not photochentically active. (C) 2002 Elsevier Science B.V. All rights reserved.

"Sensitive Determination Of Captopril By Flow Injection Analysis With Chemiluminescence Detection Based On The Enhancement Of The Luminol Reaction"
Anal. Chim. Acta 2002 Volume 463, Issue 2 Pages 249-255
Anastasios Economou, Demetrius G. Themelis, Georgios Theodoridis and Paraskevas D. Tzanavaras

Abstract: This work reports a novel flow injection (FI) method for the determination of captopril, 1-[(2S)-3-mercapto-2-methyl-propionyl]-L-proline (CPL), based on the enhancement CPL affords on the chemiluminescence (CL) reaction between luminol and hydrogen peroxide. For this purpose alkaline luminol and hydrogen peroxide solutions were mixed online, the sample containing CPL was injected into an aqueous carrier stream. mixed with the luminol-hydrogen peroxide stream and pumped into a glass flow cell positioned in front of a photomultiplier tube (PMT). The increase in the CL intensity was recorded in the form of FI peaks, the height of which was related to the CPL mass concentration in the sample. Different chemical and instrumental parameters affecting the CL response were investigated. Under the selected conditions, the log-log calibration curve was linear in the range 5-5000 µg L-1 of CPL, the limit of detection was 2 µg L-1 (at the 3s level), the RSD, s(tau) was 3.1% at the 100 µg L-1 level (n = 8) and the sampling rate was 180 injections h-1. The method was applied to the determination of CPL in pharmaceutical formulations with recoveries in the range 100±3%. (C) 2002 Elsevier Science B.V. All rights reserved.

"Integrated Analytical Pervaporation-gas-phase Absorptiometry: Theoretical Aspects And Applications"
Anal. Chim. Acta 2001 Volume 434, Issue 1 Pages 81-93
J. Galbán, I. Sanz-Vicente, J. R. Castillo and M. D. Luque de Castro

Abstract: A new pervaporator is designed in which analytical pervaporation is integrated with gas-phase absorptiometry in order to monitor the mass transfer through a hydrophobic membrane in a continuous mode. From the recording obtained, the theoretical principles which govern the steps involved in pervaporation (namely, evaporation of the volatile species into the air-gap over the liquid sample surface, diffusion through the membrane and acceptance of the diffused species in a gas phase, then recovery of the baseline by removal of the remaining analyte in the opposite direction to pervaporation) were established and expressed by the corresponding equations. Finally, a method for the determination of ammonia in the gas phase was developed in order to demonstrate the usefulness of the integrated approach and then applied to the determination of ammonia nitrogen in fertilisers.

"Electrochemical Control Of Solid Phase Micro-extraction Using Unique Conducting Polymer Coated Fibers"
Anal. Commun. 1999 Volume 36, Issue 5 Pages 203-205
Thompson P. Gbatu, Ozcan Ceylan, Karen L. Sutton, Judith F. Rubinson, Ahmed Galal, Joseph A. Caruso and Harry B. Mark Jr

Abstract: The use of a solid phase micro-extraction (SPME) method with poly(3-methylthiophene) coated platinum micro-fiber electrodes to extract arsenate ions from aqueous solutions without derivatization is described. The fibers were fabricated by cycling the working electrode between -0.20 and +1.7 V (vs. Ag/AgCl) in an acetonitrile solution containing 50 mM 3-methylthiophene monomer and 75 mM tetrabutylammonium tetrafluoroborate (TBATFB) electrolyte. All electrochemical procedures (extraction and expulsion) were conducted in a three-electrode system. After fabrication, the conducting polymer film was immersed in the sample solution and converted to its oxidized, positively charged form by applying a constant potential of +1.2 V with respect to Ag/AgCl reference electrode. Arsenate ions migrated into the film to maintain electroneutrality. Upon subsequent reversal of the potential to -0.60 V vs. Ag/AgCl, the polymer film was converted to its reduced, neutral form and the arsenate ions were expelled into a smaller volume (200 µL) Of de-ionized water for analysis using flow injection with inductively coupled plasma mass spectrometric (ICP-MS) detection.

"Derivatization Of Organometal(loid) Species By Sodium Borohydride - Problems And Solutions"
J. Chromatogr. A 2001 Volume 938, Issue 1-2 Pages 225-236
U. M. Grüter, M. Hitzke, J. Kresimon and A. V. Hirner

Abstract: Like other derivatization techniques, hydride generation is a chemical reaction that produces side-reactions leading to analytical problems. Demethylation of dimethylarsinic acid was observed to be dependent upon the pH level of the hydride generation reaction mixture. If the reaction mixture was acidic, then in addition to (CH3)(2)AsH, the monomethyl arsenic hydride [(CH3)AsH2] could be detected. Demethylation and also the formation of an unidentified arsenic species were noted when trimethyl arsonic oxide was used as derivatization educt. All of these effects depend on the pH level of the hydride generation mixture. We observed significant levels of organometal(loid) species of elements such as Ge, As, Sn, Sb, Hg and Bi in blank hydride generation mixtures. The organometal(loid) contamination was irreproducible even during 1 day using a single solution of sodium borohydride in deionized water. We concluded that the organometal(loid) contamination arises directly from the derivatization agent, sodium borohydride, itself. Use of helium purging and various adsorptive materials to decontaminate the sodium borohydride solution prior to analysis did not result in a significant decrease in organometal(loid) contamination levels. Use of a palladium-cluster stabilised with 1,10-phenanthrolin as alternative hydride generation derivatization agent was not found to be suitable, since reaction yields were poor and transmethylation reactions were noted. (C) 2001 Elsevier Science B.V. All rights reserved.

"Liquid-phase Microextraction Combined With Flow Injection Tandem Mass Spectrometry - Rapid Screening Of Amphetamines From Biological Matrices"
J. Sep. Sci. 2001 Volume 24, Issue 7 Pages 615-622
Trine Grønhaug Halvorsen, Stig Pedersen-Bjergaard, J. Léon E. Reubsaet, Knut E. Rasmussen

Abstract: Liquid-phase microextraction based on polypropylene hollow fibers was combined with flow injection tandem mass spectrometry for rapid screening of drugs in biological matrices. Amphetamine and analogues were utilised as model compounds. These drugs were extracted from 0.5 mL samples of whole blood or urine. The samples were made alkaline with 0.5 mL of 1 M NaOH and the urine samples were diluted with 3 mL water to reduce the salt concentration. The uncharged analytes were then extracted through a hollow fiber impregnated with dihexyl ether into 25 µL of 0.01 M HCl inside the hollow fiber. Parallel extraction of 20-30 samples was performed for 15 min. After extraction 20 µL of the extract was injected directly into the flow injection tandem mass spectrometry system. Atmospheric pressure ionisation operated in positive mode was used as ion spray. All analytes were detected simultaneously after 0.1 min, utilising a combination of selected ion monitoring mass spectrometry and selected reaction monitoring tandem mass spectrometry. Limits of detection (S/N = 5) varied between the compounds and were estimated to be 2-100 ng/mL in urine and 0.4-14 ng/mL in whole blood. Comparison of injection of pure acceptor solution with urine and whole blood extracts demonstrated the efficient sample clean-up by LPME. Ion suppression due to matrix effects was not seen, rendering LPME-FIA-APCI-MS-MS a promising alternative for rapid screening of drugs in biological matrices.

"Flow Injection Amperometry For The Determination Of Iodate In Iodized Table Salt"
Anal. Chim. Acta 2001 Volume 438, Issue 1-2 Pages 299-304
Jaroon Jakmunee and Kate Grudpan

Abstract: A very simple flow injection amperometric system for determination of iodate has been developed. Cyclic voltammetry was used to study reactions of iodate, iodide and iodine on a glassy carbon electrode. A single line manifold of the dow system consists of a pulse-free reagent propulsion using a simple Mariotte bottle, a home-made injection valve, and a cross flow electrochemical cell with a potentiostat for control a potential of glassy carbon working electrode at +200 mV versus Ag/AgCl electrode. Using a solution of 1.0% w/v NaCl, 0.02% w/v KI and 0.1 M HCl as a reagent and a flow rate of 2 ml/min, a linear calibration up to 25 mg/l IO3- with a detection limit of 0.5 mg/l IO3- was obtained. Relative standard deviation for 10 injections of 10 mg/l IO3- solution was 1.7%. A sample throughput of 35 injections per hour was achieved. The system was successfully applied for determination of iodate in iodized table salts, validating by the AOAC titrimetric method.

"Efficient Isolation Of The Rare Diarrhoeic Shellfish Toxin, Dinophysistoxin-2, From Marine Phytoplankton"
Toxicon 1999 Volume 37, Issue 2 Pages 343-357
Kevin J. James, Alan G. Bishop, Brendan M. Healy, Cilian Roden, Ian R. Sherlock, Marian Twohig, Rosa Draisci, Luigi Giannetti and Luca Lucentini

Abstract: The rare diarrhoeic shellfish poisoning (DSP) toxin, dinophysistoxin-2 (DTX-2), which is an okadaic acid (OA) isomer, has been isolated from a marine phytoplankton biomass that consisted mainly of Dinophysis acuta. Using a large double plankton net (length 5.9 m), bulk phytoplankton samples were collected off the south-west coast of Ireland and extracted with methanol and chloroform. Liquid chromatography coupled with ionspray mass spectrometry and tandem mass spectrometry (LC-MS, LC-MS-MS) showed the sample contained DTX-2 and OA, at a concentration of 80 pg/cell and 60 pg/cell, respectively. Flash chromatography using silica, sephadex LH20 and C-18-silica, followed by preparative reversed-phase LC, separated DTX-2 from OA. The efficiency of the separation procedures was substantially improved by the use of a bioscreen to detect DSP toxins in eluate fractions and the application of a new derivatization procedure for the chromatographic elucidation of toxin profiles with fluorimetric detection (LC-FLD). Thus, 1/1000th aliquots of eluate fractions were assayed using protein phosphatase-2A for the presence of inhibitory compounds. Positive fractions were further analyzed for DSP toxins by LC-FLD following derivatization using the hydrazine reagent, luminarine-3. The identity and purity of the free isolated DTX-2 was confirmed using flow injection analysis (FIA) and liquid chromatography (FIA-MS. LC-MS and LG-MS-MS).

"Tin Compounds And Major Trace Metal Elements In Organotin-poisoned Patients Urine And Blood Measured By Gas Chromatography-flame Photometric Detector And Inductively Coupled Plasma-mass Spectrometry"
Bull. Environ. Contam. Toxicol. 2000 Volume 65, Issue 3 Pages 277-284
Jiang Gui-bin, Zhou Qun-fang, He Bin

Abstract: During 1999 New Year's Days, more than 1000 people in southeast China's Jiangxi province, Longnan and Dingnan county, were poisoned by misusing organotin contaminated industrial lard as cooking oil, among them, hundreds people were hospitalized and three people died from it In this paper, we analyzed urine and blood samples from the patients in this incident The trace levels of inorganic and organotih compounds were determined by a simple and sensitive method which was based on the conversion of tin species into corresponding pentylated compounds and subsequent analyzed by capillary GC-FPD Total tin and 11 major trace metal elements were measured by ICP-MS To our knowledge, this is the first time to found methyltin species in human urine and blood

"Online Solid-phase Extraction Liquid Chromatography-continuous Flow Frit Fast Atom Bombardment Mass Spectrometric And Tandem Mass Spectrometric Determination Of Hydrolysis Products Of Nerve Agents Alkyl Methylphosphonic Acids By P-bromophenacyl Derivatization"
J. Chromatogr. A 1999 Volume 833, Issue 2 Pages 169-179
M. Katagi, M. Tatsuno, M. Nishikawa and H. Tsuchihashi

Abstract: For proof of the presence of chemical warfare agents sarin, soman and VX, a rapid, accurate and sensitive method which allows us to determine their hydrolysis products ethyl methylphosphonic acid, isopropyl methylphosphonic acid and pinacolyl methyl phosphonic acid was explored by using continuous flow frit fast atom bombardment (FAB) LC-MS and LC-MS-MS. After derivatization of analytes with p-bromophenacyl bromide, LC-MS-MS analyzes for screening were performed by a flow injection method. The three alkyl methylphosphonic acids (AMPAs) were eluted within 5 min, and the detection limits for the three AMPAs ranged from 1 to 5 ng/ml. For confirmation of the screening results, LC-MS-MS analysis with chromatographic separation was conducted by using a narrow bore column. The three AMPAs were all eluted with excellent separation within 25 min, and the detection limits ranged from 1 to 20 ng/ml. Quantitative measurement was performed by LC-MS in selected ion monitoring (SIM) mode with chromatogaphic separation. Linear calibration curves were obtained for the three AMPAs and the detection limits ranged from 0.5 to 3 ng/ml. The relative standard deviation for peak area ranged from 3.4 to 6.0% at 50 ng/ml for the three AMPAs.

"Determination Of Formaldehyde In Liquid, Solid And Semisolid Pharmaceuticals And Cosmetics By Flow Injection-pervaporation"
Analyst 1999 Volume 124, Issue 7 Pages 1119-1121
L. Gámiz-Gracia and M. D. Luque de Castro

Abstract: A spectrophotometric method is proposed for the determination of formaldehyde in liquid, solid and semisolid cosmetic and pharmaceutical samples, employing, for the first time in this field, the coupling of a continuous flow configuration to a pervaporation unit. The method is based on the reaction of the analyte with pararosaniline in acidic medium and subsequent formation of a colored product (alkylsulfonic acid chromophore) with sodium sulfite, which was monitored spectrophotometrically. The method was applied to samples in which the formaldehyde content is regulated by law.

"Pervaporation: A Useful Tool In Food Analysis"
Food Chem. 2000 Volume 68, Issue 4 Pages 387-394
J. Amador-Hernández and M. D. Luque de Castro

Abstract: An overview of applications of analytical pervaporation in food analysis is presented. Various designs of both the analytical pervaporation module and the continuous manifolds utilised are discussed in order to show the versatility of this non-chromatographic continuous separation technique for different challenges encountered in the automation of the overall analytical processes. Examples of the on-line analysis of liquid, semi-solid and solid samples in food and beverage industries are detailed. Finally, the potential of pervaporation as an alternative to commonly used gas-liquid separation techniques is also discussed.

"Determination Of Selenium In Nutritional Supplements And Shampoos By Flow Injection-hydride Generation-atomic Fluorescence Spectrometry"
Talanta 1999 Volume 50, Issue 4 Pages 875-880
L. Gámiz-Gracia and M. D. Luque de Castro

Abstract: A method for the determination of Se in pharmaceutical samples (nutritional supplements and shampoos) is proposed. The method involves two steps: (1) digestion of the samples and reduction of all forms of Se to Se-IV, which is complete in only 10 min by the use of a focused microwave digestor; and (2) continuous derivatization (hydride formation) and spectrometry detection by atomic fluorescence. The method can be applied over a wide range of concentrations (0.3-1300 ng mL-1 of Se) with good repeatability (RSD values lower than 4.6%). The method has been applied successfully to a reference material, and two different types of pharmaceuticals (namely, five different nutritional supplements-with Se present as sodium selenite and Se-methionine-and two shampoos, with selenium sulfide), in agreements with the certified and nominal values, respectively. Yields ranged between 86.5 and 104.8%, and good precision (RSD values lower than 4.2%) were obtained in all instances.

"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.

"Analysis Of Amino Acids And Organometallic Compounds By Particle Beam-hollow Cathode Glow Discharge Atomic Emission Spectrometry"
J. Anal. At. Spectrom. 2000 Volume 15, Issue 1 Pages 43-48
Melissa A. Dempster and R. Kenneth Marcus

Abstract: An evaluation of the particle beam-hollow cathode glow discharge atomic emission spectroscopy (PB-HC-AES) system as an element-specific detector for liquid chromatography is described for aromatic amino acids and organomercury and organolead compounds. A high-efficiency thermoconcentric nebulizer is used to introduce analyte particles into a heated hollow cathode glow discharge source for subsequent vaporization, atomization and excitation. Emission responses for hydrogen and nitrogen of amino acids in flow injection mode using 200 µL injection volumes indicate detection limits of 0.13 and 3.6 ppm elemental H and N, respectively, with RSD < 10% for triplicate injections over a concentration range of 10^-3-10^-2 M. Analysis of the response of hydrogen and nitrogen emission signal intensities to differences in amino acid stoichiometries indicates the potential of the PB-HC-AES system for the determination of empirical formulas based on H I/N I intensity ratios. Detection limits for metals and non-metals in organomercury compounds as determined through flow injection of 200 µL sample volumes fall in the sub ppm range. Liquid chromatographic separations of both amino acids and organolead compounds demonstrate the feasibility of the PB-HC-AES system as a detector for liquid chromatography. Retention times for 20 µL injections of the selected component mixtures as determined by C I emission for amino acids and Pb I emission for organolead compounds correlate well with the corresponding UV absorbance results.

"Diamine Oxidase And Putrescine Oxidase Immobilized Reactors In Flow Injection Analysis: A Comparison In Substrate Specificity"
Talanta 1999 Volume 50, Issue 1 Pages 141-148
M. -A. Carsol and M. Mascini

Abstract: Enzyme reactors for the determination of biogenic amines have been developed using diamine oxidase (DAO) from porcine kidney and from lentil and putrescine oxidase (PUO) from microorganism (Micrococcus roseus). Determination is based on the electrochemical oxidation of enzymatically produced H2O2 at platinum electrode poised at 600 mV versus Ag/AgCl. The enzymes are immobilized on controlled pore glass beads activated by glutaraldehyde in a small reactor (diameter 5 mm, length 50 mm) and included in a flow injection analysis assembly. The reactor using DAO from porcine kidney as the biochemical component responds mainly to histamine (with a detection limit of 0.5 µM), and it can be used for the evaluation of fish spoilage. The PUO reactor shows a significant response only to putrescine. It is linear in the range 0.07-500 µM. The reactor using DAO from lentil is sensitive to several amines and it could be useful to evaluate a total value. The buffer used for both types of oxidase based sensors is phosphate 0.10 M pH 7.0 containing 0.10 M NaCl.

"Development Of Phosphine Reagents For The High-performance Liquid Chromatographic-fluorometric Determination Of Lipid Hydroperoxides"
J. Chromatogr. A 2000 Volume 881, Issue 1-2 Pages 159-170
Kazuaki Akasaka and Hiroshi Ohrui

Abstract: Phosphine reagents were designed and synthesized as a new type of fluorescent reagents for the determination of lipid hydroperoxides in foodstuff and biological materials. All phosphine reagents prepared had no fluorescence but their oxides, which were produced by the reaction of the phosphines with hydroperoxides, had strong fluorescence. Among the phosphine reagents prepared, diphenyl-1-pyrenylphosphine had the most suitable properties as a fluorescent reagent and was successfully applied to the determination of hydroperoxides by batch, how injection and HPLC post-column methods.

"Flow Injection-liquid Chromatography-cold Vapor Atomic Absorption Spectrometry For Rapid Determination Of Methyl And Inorganic Mercury"
Analyst 2000 Volume 125, Issue 6 Pages 1193-1197
Johanna Qvarnstr&ouml;m, Qiang Tu, Wolfgang Frech and Christian L&uuml;dke

Abstract: A previously described system for determining low concentrations of mercury species in environmental samples using flow injection high-performance liquid chromatography cold vapor atomic absorption spectrometry (FI-HPLC-CVAAS) has been further developed with respect to time of analysis, long term signal stability, memory effects, detection limits, and environmental friendliness. Methyl and inorganic mercury were determined without pre-treatment in brackish water and in digested biological certified reference materials, DOLT-2 and TORT-2. Results were compared with those obtained by gas chromatography microwave-induced plasma atomic emission spectroscopy (GC-MIP-AES) using either butylation with a Grignard reagent or ethylation with sodium tetraethylborate. With the FI-HPLC-CVAAS system, absolute detection limits are 1.7 pg and 3.4 pg for methyl and inorganic mercury, respectively. Mercury species in a sample can be determined at the 0.4 ng L-1 level within 5 min. For lower concentrations the time for analysis has to be increased.

"Rapid And Selective Determination Of Ammonium By Fluorimetric Flow Injection Analysis"
Fresenius J. Anal. Chem. 2000 Volume 366, Issue 8 Pages 825-829
H. Mana, U. Spohn

Abstract: Selective and sensitive procedures for the determination of ammonium in river water and diluted urine were developed by using flow injection analysis equipment. The methods are based on the derivatization of ammonia with o-phthaldehyde (OPA) and thioglycolate under alkaline conditions. The formed isoindole derivative is detected fluorimetrically at an excitation wavelength of 415 nm and an emission wavelength of 485 nm. The derivatization only takes 15 to 20 s at room temperature to achieve the maximum sensitivity. The optimized OPA reagent shows a surprisingly high selectivity for ammonium in the presence of many primary amines. With respect to the analysis of turbid and fluorescent sample solutions the selectivity can be improved by separating the ammonia through a microporous membrane from the OPA reagent. Without this separation step ammonia can be detected in the range between 0.05 and 100 µM with excellent linearity. After the insertion of an optimized membrane separation cell ammonia can be determined in the linear range between 0.2 µM and 20 mM.

"Reversed Flow Injection Manifold For The Spectrophotometric Determination Of Captopril Based On Its Inhibitory Effect On The Co(II)-2,2 -dipyridyl-2-pyridylhydrazone Complex Formation"
Talanta 2002 Volume 57, Issue 3 Pages 575-581
Paraskevas D. Tzanavaras, Demetrius G. Themelis, Anastasios Economou and Georgios Theodoridis

Abstract: The present work reports a now, simple and rapid reversed flow injection (r-FI) method for the accurate and precise spectrophotometric determination of captopril (CPL) in pharmaceutical formulations. The method is based on the inhibitory effect of CPL on the complex formation of Co(II) with 2,2-dipyridyl-2-pyridylhydrazone (DPPH). The chemical and FI variables were studied and optimized. The calibration graph was linear in the range 0-250 mg L-1 CPL, at a sampling rate of 60 injections per hour. The method was found to be very precise [s(r) = 0.8% at 100.0 mg L-1 CPL (n = 12)] and the 3s detection limit (c(L) = 2.5 mg l-1) was quite satisfactory. Its application to commercially available pharmaceuticals produced excellent results, with a mean relative error of e(r) < 1.0%. (C) 2002 Elsevier Science B.V. All rights reserved.

"Detection Of Oxidative Species For 4-phenoxyphenol Derivatives During The Electrospray Ionization Process"
Rapid Commun. Mass Spectrom. 2000 Volume 14, Issue 9 Pages 756-764
Yunhui Wu, Hong Wang

Abstract: Analyses by flow Injection as well as liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) were performed with four 4-phenoxyphenol derivatives. When ambient temperature nitrogen gas was used to facilitate solvent evaporation, [M + H](+), [M + NH4](+), and [2M + NH4](+) ions were observed as the major ions. As the nitrogen gas temperature increased from ambient to 250 and 450°C, [M](+.), [M - 1](+) and [M + 15](+) ions were the predominant ions. Heat-induced oxidation was found to be the primary source for the formation of oxidative species. Aqueous solvents were found to be essential for the formation of the [M + 15](+) ions. The [M](+.) and [M + 15](+) ions were further characterized by tandem mass spectrometry. Based on the MS/MS data, it was proposed that the [M + 15](+) ions were the in-source generated 1,2-quinone ions. Copyright

"Electrochemical Oxidation Of Alkylphenols On ECR-sputtered Carbon Film Electrodes With Flat Sub-nanometer Surfaces"
J. Electrochem. Soc. 2002 Volume 149, Issue 12 Pages E479-E484
Tianyan You, Osamu Niwa, Masato Tomita, Toshihiro Ichino, and Shigeru Hirono

Abstract: We prepared a new carbon film electrode by the electron-cyclotron-resonance (ECR) plasma sputtering method. The film is amorphous-like and different from the glassy carbon (GC), highly oriented pyrolytic graphite and diamond films that have previously been studied for use as electrode materials. We used cyclic voltammetry (CV) and flow injection analysis (FIA) with amperometric detection to compare the electrochemical properties of an ECR-sputtered carbon (SC) film electrode with those of a GC electrode and carbon film deposited by thermal chemical vapor deposition (T-CVD). The ECR-SC film electrode exhibited better electrochemical properties than the GC and T-CVD carbon electrodes, namely, a lower background current, a wider working potential window, and better reproducibility. CV with the ECR-SC film electrode did not reveal any large reduction in rho-nonylphenol (NP) and other alkylphenol (AP) peaks. In contrast, we observed a clear reduction in the CV and FIA peaks when we measured NP with GC and T-CVD carbon electrodes, indicating that there was much less deactivation from the NP oxidation products on the ECR-SC electrode surfaces. The NP calibration curve at the ECR-SC electrode in a flow system showed a linear concentration range of 0.125-10 muM with a detection limit of 50 nM (S/N = 3). (C) 2002 The Electrochemical Society.

"Use Of Amino-carbonyl Reaction And Chemiluminescence Detection To The Flow Injection Determination Of Some Amino Acids"
Talanta 2001 Volume 54, Issue 1 Pages 107-113
J. Micha&#322;owski and A. Koj&#322;o

Abstract: Some amino acids were found to react with carbonyl functional groups of humic acid. Products of this reaction give strong chemiluminescence during their oxidation with N-bromosuccinimide (NBS) in alkaline solution. Humic acids from different sources produced similiar signal magnitude. This effect was employed to the flow injection determination of glycine and arginine in pharmaceutical formulations with considerable selectivity against different amino compounds. The proposed method is fast and simple. Detection limit is 0.20 and 0.25 mg L-1 for glycine and arginine respectively, and 115 samples per h can be determined.

"Flow Injection Analysis Of Some Nonapeptides Derivatized With 4-fluoro- 7-nitrobenzo-2,1,3-oxadiazole"
Biomed. Chromatogr. 1997 Volume 11, Issue 2 Pages 109-110
W. R. G. Baeyens*, G. Van der Weken, Y. Vanden Bossche, A. van Overbeke, K. Imai

Abstract: 3 References
Peptides Fluorescence