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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Richard P. Baldwin

Abbrev:
Baldwin, R.P.
Other Names:
Address:
Department of Chemistry, University of Louisville, Louisville, KY 40292
Phone:
(502) 852-5892
Fax:
(502) 852-8149

Citations 14

"Chemically Modified Electrodes In Liquid Chromatography [and Flow Injection Analysis] Detection: A Review"
Talanta 1991 Volume 38, Issue 1 Pages 1-16
Richard P. Baldwin*, Karsten N. Thomsen,

Abstract: Recent trends in the use of chemically modified electrodes are reviewed, with 96 references. Specific application areas are identified as those involving: (i) permselective coatings; (ii) immobilized electron transfer mediators to catalyse slow reactions; (iii) enzyme modifiers to provide biological surface activity; and (iv) ion-exchange coatings for electrochemical detection of non-electroactive anions and cations.
LC Electrode Ion exchange Catalysis Review

"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

"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.

"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

"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

"Constant Potential Amperometric Detection Of Underivatized Amino-acids And Peptides At A Copper Electrode"
Anal. Chem. 1991 Volume 63, Issue 17 Pages 1702-1707
Peifang Luo, Fuzhen Zhang, and Richard P. Baldwin

Abstract: Electrochemical detection of amino-acids and peptides at a Cu electrode was evaluated as a means of detection of such compounds in flow injection analysis and HPLC. The optimum conditions for amperometric detection were an operating potential of +0.55 V vs. Ag - AgCl in 0.15 M NaOH as electrolyte. Detection limits for amino-acids were 1 to 50 pmol.
Amino Acids Peptides Amperometry HPLC Electrochemical analysis Electrode Potentiometry

"Amperometric Detection Of Non-electroactive Cations In Flow Systems At A Cupric Hexacyanoferrate Electrode"
Anal. Chem. 1989 Volume 61, Issue 23 Pages 2594-2598
Karsten N. Thomsen and Richard P. Baldwin

Abstract: A vitreous carbon electrode coated with an electro-deposited film of Cu3[Fe(CN)6]2 was evaluated as a sensor for non-electroactive cations in flow injection analysis and ion chromatography. The activity of the electrode in the flow system was similar to that seen for static solution in that reduction of the film was selectively enhanced by K+ and NH4+. Consequently, these ions could be detected indirectly as cathode peaks. HPLC detection limits of 0.5 µM, corresponding to 10 pmol injected, were obtained for both ions at an applied potential of +0.45 V vs. Ag - AgCl. Coating the electrode with a supporting overlayer of Nafion improved the stability and reproducibility; coefficient of variation were 1 to 5% over several hours.
Potassium Ammonium Electrode HPIC Amperometry Detection limit Nafion membrane

"Electrocatalysis And Detection Of Amino-sugars, Alditols And Acidic Sugars At A Copper-containing Chemically Modified Electrode"
Anal. Chem. 1989 Volume 61, Issue 20 Pages 2258-2263
Sunil V. Prabhu and Richard P. Baldwin

Abstract: The use of the electrode described previously (Anal. Abstr., 1990, 52, 4J112) for the oxidative detection of simple sugars has been extended. Cyclic voltammetric scans for the compounds showed a broad oxidation in the region of +0.4 to +0.6 V vs. Ag - AgCl. When used in flow injection analysis and LC, detection limits were in the pmol to nmol range. With flow injection the coefficient of variation (n = 60) for 10 µM-gluconic acid was 4.9% and in the analysis of a tobacco leaf extract by LC, the standard deviation, e.g., for 3.7% of glucose was 0.2%.
Gluconic acid Leaves Electrode Voltammetry Detection limit Catalysis

"Constant-potential Amperometric Detection Of Carbohydrates At A Copper-based Chemically Modified Electrode"
Anal. Chem. 1989 Volume 61, Issue 8 Pages 852-856
Sunil V. Prabhu and Richard P. Baldwin

Abstract: A chemically modified electrode was prepared by coating a vitreous-carbon electrode with a Cu(II) layer, which decreased the overpotential for carbohydrate oxidation compared to that at unmodified carbon electrodes. The electrode was used for constant potential amperometric detection of reducing and non-reducing sugars separated by HPLC on a column (15 cm x 4 mm) of Dionex HPIC-AS6. The Cu layer catalyzed the sugar oxidation in basic solution when a potential sufficiently positive to generate Cu(III) was applied. In flow injection analysis and HPLC, electrode response was stable for >5 h (signal loss 10%). With anion-exchange chromatography in 0.15 M NaOH, mono- and disaccharides were separated and detected in sub ng amounts at an applied potential of +0.48 V vs. Ag - AgCl.
Carbohydrates Electrode Amperometry

"Catalytic Reduction Of Myoglobin And Haemoglobin At Chemically Modified Electrodes Containing Methylene Blue"
Anal. Chem. 1988 Volume 60, Issue 20 Pages 2263-2268
Jiannong Ye and Richard P. Baldwin

Abstract: Electrodes that respond electrocatalytically to myoglobin(I) and haemoglobin(II) were prepared by immersing the polished end surface of spectroscopic-grade graphite rods (5-mm diameter) for 60 s in a stirred 0.01% solution of methylene blue(III) in 0.1 M phosphate buffer of pH 5.3, then rinsing the rods with water. Cyclic voltammetric studies showed that the presence of I or II caused an increase in the reduction current and a decrease in the oxidation current of III. The electrodes were stable for several hours, and could be regenerated by polishing and re-immersion in the III solution. The electrodes could be used as detectors in flow injection analysis or reversed-phase HPLC (details given) by operation at -0.12 V vs. Ag - AgCl, and gave detection limits of 10 and 20 pmol injected for I and II, respectively; response was rectilinear over 2 to 3 orders of magnitude.
Myoglobin Hemoglobin HPLC Electrode Detector

"Flow Injection Analysis Of Electroinactive Anions At A Polyaniline Electrode"
Anal. Chem. 1988 Volume 60, Issue 18 Pages 1979-1982
Jiannong Ye and Richard P. Baldwin

Abstract: The electrode was prepared by immersing a polished Pt electrode in stirred 1.0 M H2SO4 containing 0.1 M aniline and scanning three complete cycles between -0.2 and +1.1 V vs. a Ag - AgCl reference electrode at 20 mV s-1. Cyclic voltammetry (details given) in 0.2 M Na acetate buffer (pH 6.0) containing 0.1 M ClO4- or flow injection analysis of the same medium or one containing 0.2 M glycine, with detection at 0.2 or 0.5 V, respectively, gave best results for NO3-, Cl-, SO42-, Br-, NO2- and ClO4-, e.g., the calibration graph for flow injection analysis of NO3- was rectilinear over three orders of magnitude, and the detection limit was ~0.1 ppm with use of the glycine mobile phase.
Anions, electroinactive Electrode Electrode Voltammetry Indirect Interferences

"Phthalocyanine-containing Chemically Modified Electrodes For Electrochemical Detection In Liquid Chromatography/flow Injection Systems"
Anal. Chem. 1984 Volume 56, Issue 8 Pages 1514-1517
Kelvin M. Korfhage, K. Ravichandran, and Richard P. Baldwin

Abstract: In order to minimize overvoltage effects, carbon-paste electrodes were modified with cobalt phthalocyanine; their use was investigated as electrocatalytic sensors in the HPLC determination of hydrazine. Cyclic voltammograms are presented for modified and unmodified electrodes with a SCE as reference and a platinum-wire counter-electrode. The scan rate was 10 mV s-1. The HPLC system consisted of a Waters model M6000A pump, Rheodyne model 7125 injector with 20 µL sample loop and IBM model EC/230 amperometric detector and the column was replaced by a stainless-steel tube (5 ft x 0.01 in). A Bioanalytical Systems model TL-3 thin-layer carbon-paste electrode assembly was used at -0.1 V vs. a silver - AgCl electrode. The mobile phase was 0.20 M NaOH at 0.5 mL min-1. The detection limit was 6.4 pg (0.2 pmol) for hydrazine.
Hydrazine HPLC Electrode Voltammetry

"Comparison Of Metallic Electrodes For Constant-potential Amperometric Detection Of Carbohydrates, Amino Acids And Related Compounds In Flow Systems"
Anal. Chim. Acta 1991 Volume 244, Issue 2 Pages 169-178
Peifang Luo, Fuzhen Zhang and Richard P. Baldwin

Abstract: Constant-potential amperometric detection of carbohydrates, amino acids, and other aliphatic organic compounds is possible by means of their oxidation in alkaline solution at a variety of metal/metal oxide electrodes including Pt, Au, Cu, Ni, Ag and Co. The experimental conditions required for optimum detection and the analytical performance obtainable vary widely for different electrode materials and analytes. In this work, the cyclic voltammetric behavior exhibited by selected analytes (glucose, glycine, lactic acid, ethylamine and ethanol) at each of these electrodes was used to determine the optimum potentials suitable for flow detection so that the capabilities of the different metal electrodes could be evaluated and systematically compared. In general, the Cu electrode was found to provide superior detection capabilities in terms of its range of response, detection limits and especially stability. Despite the fact that Pt and Au are typically used only with a pulsed applied potential, both can provide long-lived constant-potential detection of carbohydrates and other analytes at low concentrations if the potentials ere carefully chosen and the electrodes are allowed to undergo an initial stabilization period.
Amino Acids Carbohydrates Amperometry LC Electrochemical analysis Electrode Electrode Electrode Potentiometry Catalysis Injection technique

"Voltammetric Determination Of Doxorubicin In Urine By Adsorptive Preconcentration And Flow Injection Analysis"
Anal. Chim. Acta 1985 Volume 176, Issue 1 Pages 105-112
Edward N. Chaney, Jr. and Richard P. Baldwin

Abstract: A flow injection system has been applied to the earlier manual procedure (Anal. Chem., 1982, 54, 2556). The sample (6 µL) is injected into a carrier stream (0.1 mL min-1) of 0.2 M acetate buffer (pH 4.5) and passed into a detector cell equipped with a thin-layer carbon-paste working electrode (area 0.071 cm2) and a silver - AgCl reference electrode. A potential of +0.3 V is applied to the carbon-paste electrode until a stable response is obtained. Then the potential is scanned from +0.3 to +0.7 V in the differential pulse mode at 2 or 5 mV s-1. The height of the oxidation peak at +0.57 V is rectilinearly related to concentration. in the range 1 to 1000 nM-I. In order to overcome variable matrix effects in urine samples, the method of standard additions is used for quantitation. The flow injection procedure gives better discrimination against adsorbable sample components (e.g., uric acid) than the manual technique.
Doxorubicin Urine Electrode Voltammetry Preconcentration Standard additions calibration