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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Hari Gunasingham

Abbrev:
Gunasingham, H.
Other Names:
Address:
Department of Chemistry, National University of Singapore, Kent Ridge Crescent, 0511, Singapore
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Citations 15

"Analytical Applications Of The Wall-jet Detector"
Trends Anal. Chem. 1988 Volume 7, Issue 6 Pages 217-221
Hari Gunasingham

Abstract: The wall-jet detector offers a number of advantages in applications to continuous-flow analysis such as in liquid chromatography and flow injection analysis. Among the advantages is the ability to use a simple detector design and the fact that the solution volume in the detector is not constrained. However, high sensitivity and resolution can be achieved.
Electrode Review

"Cyclic Voltammetry Of Some Quinones And Nitroaromatic Compounds Using A Mercury Film Wall-jet Detector And Flow Injection Analysis"
J. Singapore Natl. Acad. Sci. 1987 Volume 16, Issue 1 Pages 80-86
Ang, K. P.; Gunasingham, H.; Tay, B. T. (SFS)

Abstract: A technique combining flow injection analysis and cyclic voltammetry (CV) to study electrochemical reactions is described. The technique was used to study the redox behavior of a number of nitro and quinone compounds at a bare glassy carbon electrode (GCE) and a preplated Hg film electrode (MFE). The MFE can be automatically renewed under computer control, thus minimizing surface contamination. It also offers a number of benefits over the bare GCE which include more well-defined CV curves, more reversible behavior, and a wider cathodic range. The CV of 1-nitroanthraquinone using this equipment is described for the first time. (SFS)
Quinones Nitro compounds Voltammetry Electrode Electrode

"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

"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

"Clinical Evaluation Of Amperometric Enzyme Electrodes In Continuous-flow Analysis For Glucose In Undiluted Whole Blood"
Clin. Chem. 1990 Volume 36, Issue 9 Pages 1657-1661
H Gunasingham, CH Tan and TC Aw

Abstract: We have evaluated the carbon-paste enzyme/wall-jet electrode in continuous-flow analysis for glucose in undiluted whole blood. Responses of the electrode to protein-based and aqueous samples under wall-jet configuration are described. Imprecision in the flow injection mode was less than 2% for glucose values in the usual analytical range (1-25 mmol/L). The dynamic range for glucose was from 0.03 to 45 mmol/L, with about 100% recovery of added substrate. The performance of the electrode (y) in flow injection and steady-state modes was compared with a colorimetric method (x; Kodak Ektachem XR700), yielding linear-regression equations of y = 1.152x + 0.295 and y = 0.979x + 0.500, respectively. Among the anticoagulants, blood preservatives, and interfering substances investigated, only ascorbic acid gave a significant positive bias. The electrode exhibited good stability for analyzes of undiluted whole-blood samples.
Glucose Whole Amperometry Electrode Electrode Electrode Clinical analysis Interferences Method comparison

"Electrochemically Modulated Optrode For Glucose"
Biosens. Bioelectron. 1992 Volume 7, Issue 5 Pages 353-359
Hari Gunasingham and Chin-Huat Tan

Abstract: One of the problems with fiber-optic sensors is the difficulty of finding reversible indicator reagents. This is a particular problem for fiber-optic glucose sensors. The development of an electrochemically modulated fiber-optic probe or optrode has been proposed as a convenient solution. Here the indicator reagent is regenerated electrochemically. In this work a design is proposed that offers considerable advantages in practical applications. In particular, it can be used in the same way as conventional optrodes. The optimization of working parameters and the application of the optrode to flow analysis under steady-state and flow injection conditions is described.
Glucose Optrode Sensor Sensor Optical fiber Optimization

"Fiber-optic Glucose Sensor With Electrochemical Generation Of Indicator Reagent"
Anal. Chem. 1990 Volume 62, Issue 7 Pages 755-759
Hari Gunasingham, Chin Huat Tan, and Jimmy K. L. Seow

Abstract: The prep. is described of a reversible enzyme-based optical-fiber sensor, involving the electrochemical regeneration of the optically active redox mediator tetrathiafulvalene as the indicator. The performance of the sensor as a thin-layer cell configuration was evaluated in flow injection and steady-state analyzes giving a rectilinear calibration graph for ~12 and 3 mM, respectively, and a detection limit of 0.2 mM glucose. Potential interfering species such as O and organic species had no significant effect on detector response. The response was compared with an amperometric detector.
Glucose Amperometry Sensor Enzyme Electrochemical reagent generation Redox Calibration Detection limit Interferences Optical fiber

"Automated Mercury Film Electrode For Flow Injection Analysis And High Performance Liquid Chromatography Detection"
Anal. Chem. 1986 Volume 58, Issue 7 Pages 1578-1580
Hari Gunasingham, B. T. Tay, and K. P. Ang

Abstract: Microprocessor control was used in conjunction with a mercury-film wall-jet electrode to enable the reproducible control of formation of a fresh film surface, stripping and analysis. The application of the cited electrode for reductive detection in flow injection analysis and HPLC was studied. The mean coefficient of variation for the HPLC determination of nitro- and quinone compounds with this electrode as detector was 3% for injections in the range of 3.2 to 40 µg of analyte.
Nitro compounds Quinone Electrode Polarography

"Mercury(II) Acetate-Nafion Modified Electrode For Anodic-stripping Voltammetry Of Lead And Copper With Flow Injection Analysis"
Anal. Chim. Acta 1994 Volume 291, Issue 1-2 Pages 81-87
Ruelito R. Dalangin and Hari Gunasingham*

Abstract: Ethanolic solution of mercury(II) acetate and Nafion perfluorosulfonate resin were mixed and used to coat the polished vitreous carbon electrode surface. The modified electrode was used in the flow injection determination of trace metals using a wall-jet detector. The wall-jet cell was filled with supporting electrolyte at ~1.2 ml/min and once all three electrodes were submerged, the pump was switched off and a potential of -1.0 V was applied for 5 min. The electrolyte flow was started up again at ~1.5 ml/min and the potentials were held at 0.0 V for 2 min. Sample was delivered to the cell for 45 s and a hold time of 15 s was observed before stripping the metals in stationary solution at 20 mV/s. The effects of Hg loading, Nafion loading, pH, flow rate, electrode-inlet distance and the presence of organic surfactants was studied (discussed). The method was applied to the determination of Pb2+ (0.07-2.8 µg/ml) and Cu2+ (0.5-2.3 µg/ml) in industrial effluents; detection limits were 5 and 4 ng/ml, respectively. RSD for the determination of 0.483 µM-Pb and 1.57 µM-Cu were 7.16 and 8.10%, respectively.
Lead(2+) Copper(II) Water Voltammetry Electrode

"Comparative Study Of First-generation, Second-generation And Third-generation Amperometric Glucose Enzyme Electrodes In Continuous-flow Analysis Of Undiluted Whole-blood"
Anal. Chim. Acta 1990 Volume 234, Issue 2 Pages 321-330
Hari Gunasingham and Chin-Huat Tan, Tar-Choon Aw

Abstract: First-, second- and third-generation amperometric glucose enzyme electrodes were compared under flow injection and steady-state conditions for the monitoring of undiluted whole blood. Measurements were made in a large volume wall-jet cell (illustrated) with a four-way manual injection value, a sample loop of 25 µL or 200 µL for flow injection and steady-state modes, respectively, and a graphite counter electrode vs. Ag - AgCl. Use of first-generation electrodes, based on H2O2 detection at a Pt electrode, was limited by their instability. Second-generation electrodes in which re-oxidation of glucose oxidase occurs by a mediator are more suitable for blood analysis however the choice of mediator is important. With regard to the rectilinearity and stability, tetrathiafulvalene achieves better results than dimethyl ferrocene. Third-generatin electrodes based on tetrathiafulvaleine - teracyanoquinodimethane where direct oxidation of glucose oxidase occurs, were also useful, but display lower stability and a smaller dynamic range than second-generation devices. The calibration graphs for first, second and third-generation electrodes were rectilinear up to 10, 35 and 25 mM for steady-state analysis and 25, 80 and 60 mM for flow injection analysis, respectively.
Glucose Whole Amperometry Electrode Electrode Electrode Enzyme Calibration Apparatus Detector

"Conducting Organic Salt Amperometric Glucose Sensor In Continuous-flow Monitoring Using A Wall-jet Cell"
Anal. Chim. Acta 1990 Volume 229, Issue 1 Pages 83-91
Hari Gunasingham and Chin-Huat Tan

Abstract: A paste was prepared by mixing tetrathiafulvalene - 7,7,8,8-tetracyanoquinodimethane complex salt with 10% of Nujol (with or without added graphite) and packed into the well of an electrode consisting of a PTFE holder and a graphite disc. The paste was successively covered with glucose oxidase, bovine serum albumin - glutaraldehyde (4:1) and a 0.03 µm-pore polycarbonate membrane. The electrode was used with a large-volume wall-jet cell, a graphite counter-electrode and Ag - AgCl reference electrode in an automated system for (i) flow injection or (ii) steady-state analysis. At 0.2 V a rectilinear response was observed for up to 60 mM glucose (I) by method (i) or 30 mM by method (ii). Results obtained by method (ii) were more consistent than those by method (i). For determination of 5.5 to 11 mM I in whole blood at 0.15 V and 0.5 mL min-1, results by method (ii) were lower than those by method (i) and were in better agreement with results obtained with use of a Haemo-glutotest 20-800R (Boehringer Mannheim) test strip.
Glucose Whole Amperometry Electrode Electrode Sensor Complexation Method comparison

"Carbon Paste-tetrathiafulvalene Amperometric Enzyme Electrode Forthe Determination Of Glucose In Flowing Systems"
Analyst 1990 Volume 115, Issue 1 Pages 35-39
Hari Gunasingham and Chin-Huat Tan

Abstract: The development of a carbon paste-tetrathiafulvalene amperometric enzyme electrode for the determination of glucose in flowing streams is described. The enzyme electrode is operated in a flow-through detector based on the wall-jet configuration under flow injection (FI) and steady-state (SS) conditions. Under FI conditions, high precision (0.6%) and sample throughput (120 samples h-1) are possible. Moreover no pre-conditioning of the electrode is required. The flow system is suitable for the determination of glucose in whole blood without sample dilution. With proper orientation of the jet with respect to the enzyme electrode, high accuracy can be obtained under SS conditions. The electrode was prepared by placing a graphite disc (3 mm diameter x 2 mm thick) into a PTFE holder leaving a well 1 mm deep into which was packed carbon paste containing tetrathiafulvalene (20%) in Nujol. The polished paste surface was coated with glucose oxidase and dried, covered with 2.5 µL of bovine serum albumin (5%) and glutaraldehyde (2.5%) and a polycarbonate membrane. Glucose was determined directly in whole blood by flow injection and steady-state methods in a large volume wall-jet cell vs. Ag - AgCl using 25 or 250 µL samples, respectively. No electrode pre-conditioning was necessary. Flow injection gave high precision and sample throughput (120 samples h-1); high accuracy can be attained for steady-state conditions with careful jet orientation.
Glucose Whole Electrode Amperometry Enzyme Detector

"Platinum-dispersed Nafion-film-modified Glassy Carbon As An Electrocatalytic Surface For An Amperometric Glucose Enzyme Electrode"
Analyst 1989 Volume 114, Issue 6 Pages 695-698
Hari Gunasingham and Chee Beng Tan

Abstract: A Nafion film was coated on an electrochemically pre-treated vitreous-carbon electrode, and Pt particles were deposited on the film by potential cycling between +0.7 and -0.15 V. Glucose oxidase was subsequently immobilized on the electrode with use of bovine serum albumin and glutaraldehyde and covered with a polycarbonate membrane. The electrode was incorporated in a flow injection system containing a large-volume wall-jet detector with a Ag - AgCl reference electrode. The electrode exhibited better stability and selectivity than did a solid Pt electrode, and showed comparable sensitivity. The calibration graph was rectilinear up to 30 mM glucose. The electrode was applied to determine glucose in blood; results agreed with those obtained with a Boehringer Refolux monitor.
Glucose Blood Electrode Electrode Amperometry Apparatus Detector

"Platinum-dispersed Nafion-modified Glassy Carbon Electrode For The Determination Of Hydrogen Peroxide In A Flow Injection System"
Analyst 1988 Volume 113, Issue 4 Pages 617-620
Boon-Tat Tay, Kok-Peng Ang and Haritharan Gunasingham

Abstract: The cited electrode was prepared by electro-deposition of Pt particles into Nafion-coated vitreous carbon, by potential cycling between +0.7 and -0.15 V in acidic K2PtCl6 solution at a scan rate of 50 mV s-1. Compared with Pt, vitreous carbon and Pt-modified vitreous carbon electrodes, the Nafion - vitreous carbon system displayed increased stability. Linear-sweep voltammograms of 10 mM H2O2 in 0.1 M phosphate buffer (pH 7.4) at the various electrodes were obtained; at Pt loading levels 150 µg cm-2 the Pt - Nafion - vitreous carbon electrode showed a higher response than the Pt electrode. An application of the cited electrode to the flow injection analysis - electrochemical detection of H2O2 is described. Generally the rectilinear working range was from 1 µM to ~50 mM H2O2.
Hydrogen peroxide Electrode Voltammetry Apparatus

"Determination Of Glucose Using Flow Injection With A Carbon Fiber Based Enzyme Reactor"
Analyst 1987 Volume 112, Issue 10 Pages 1433-1435
K. P. Ang, H. Gunasingham, B. T. Tay, V. S. Herath, P. Y. T. Teo, P. C. Thiak, B. Kuah and K. L. Tan

Abstract: A reactor of immobilized glucose oxidase(I) covalently coupled to a bundle (~105) of carbon fibers by the method described by Bourdillon et al. (J. Am. Chem. Soc., 1980, 102, 423) is used with a wall-jet detector in the flow injection analysis of H2O2 produced by the enzymatic reaction of I with glucose. The working platinum electrode is operated at +0.7 V vs. silver - AgCl, the max. response being achieved at 1.45 mL min-1 with phosphate buffer at pH 7.4. The response increases with increase in temperature of the reactor. Response is rectilinear from 3 to 30 mM glucose. The coefficient of variation is 2% (n = 100).
Glucose Amperometry Electrode Electrode Carbon fiber Heated reaction Immobilized enzyme