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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Greg M. Swain

Abbrev:
Swain, G.M.
Other Names:
Address:
Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322 USA
Phone:
435-797-1626
Fax:
435-797-3390

Citations 6

"Electro-oxidation And Amperometric Detection Of Chlorinated Phenols At Boron-Doped Diamond Electrodes: A Comparison Of Microcrystalline And Nanocrystalline Thin Films"
Environ. Sci. Technol. 2004 Volume 38, Issue 13 Pages 3674-3682
Grace W. Muna, Natasha Tasheva and Greg M. Swain

Abstract: We report on the electro-oxidation and amperometric detection of phenol and chlorinated phenols, the latter coupled with flow injection analysis (FIA) and high performance liquid chromatography (HPLC), using boron-doped microcrystalline and nanocrystalline diamond thin-film electrodes. The low background current, good response without extensive pretreatment, and low susceptibility to fouling are properties that make diamond an attractive new electrode for monitoring this class of pollutants. Cyclic voltammetric studies were performed to evaluate the redox response of phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, and pentachlorophenol (PCP) in phosphate buffer, pH 3.5, as a function of the potential scan rate and cycle number. The diamond electrode performance for the amperometric detection of these contaminants in FIA-EC and HPLC-EC was evaluated in terms of the linear dynamic range, limit of quantitation, sensitivity, response precision, and response stability. Both diamond types yielded low mass limits of quantitation of 100-1000 pg for all the phenolic compounds in FIA-EC, except PCP which was 3 ng, and 100-600 pg for all the compounds in HPLC-EC. In all cases, the S/N was 3 or greater. Both electrode types also exhibited good sensitivity, excellent response reproducibility (av 2.7% for FIA-EC and av 4.2% for HPLC-EC), and superb response stability for all the analytes. The electrodes could be used from days to weeks in the measurement with only a periodic soak in distilled 2-propanol required to maintain optimum performance. Both types of diamond outperformed glassy carbon, which exhibited short-lived responsiveness as a consequence of fouling by reaction products and potential-dependent changes in the electrode's physiochemical properties. The use of the HPLC-EC assay for the determination of 2-chlorophenol in a contaminated soil sample is also demonstrated.

"Diamond Optically Transparent Electrodes: Demonstration Of Concept With Ferri-ferrocyanide And Methyl Viologen"
Anal. Chem. 2001 Volume 73, Issue 5 Pages 908-914
Jerzy K. Zak, James E. Butler, and Greg M. Swain

Abstract: A new type of optically transparent electrode is reported on-an electrically conductive diamond thin film. The electrode was free-standing (0.38 mm thick and 8 mm in diameter), mechanically polished to a 7 nm rms roughness over a 10 m linear distance, boron-doped (0.05% B/C in the reactant gas mixture), and mounted in a thin-layer transmission cell. The electrode has a short-wavelength cutoff of ~225 nm, which is the indirect band gap of the material, and transmits light out to at least 1000 nm. In theory, the electrode has an optical window from 225 nm well out into the far-infrared, except for the boron acceptor band and the intrinsic multiphonon absorptions. The electrode was used to electrooxidize ferrocyanide to ferricyanide, and the absorbance change associated with the formation of the oxidized product (max = 420 nm) was spectroscopically monitored. The electrode was also used to electroreduce methyl viologen (MV2+) to the cation radical (MV+) and the neutral (MV0). The depletion of MV2+ (max = 257 nm) and formation of MV+ (max = 398 and 605 nm) were spectroscopically monitored.
Selectivity

"Voltammetric And Amperometric Investigations Of Azide Oxidation At The Basal Plane Of Highly Oriented Pyrolytic Graphite"
Anal. Chem. 1999 Volume 71, Issue 20 Pages 4603-4608
Jishou Xu and Greg M. Swain

Abstract: The electrochemical oxidation of dissolved azide anion was studied at the basal plane of highly oriented pyrolytic graphite. Cyclic and linear sweep voltammetry and differential pulse voltammetry were employed to study the oxidation reaction mechanism in neutral pH as a function of the potential sweep rate, analyte concentration, and electrolyte composition and in the presence of adsorbed anthraquinone-2,6-disulfonate (2,6-AQDS). The linear dynamic range in the differential pulse voltammetric measurements was 4 orders of magnitude and the estimated limit of detection (SNR = 3) was ~2.3 x 10^-7 M (9.7 ppb). The electron-transfer kinetics for azide oxidation appear rapid at this surface, and the voltammetric features are independent of the fraction of exposed edge plane, the presence of surface oxides, the electrolyte composition, and the adsorption of 2,6-AQDS. The reaction proceeds by an EC(dim) mechanism. Amperometric detection results for flow injection analysis (FIA) and ion chromatography are also presented. A linear dynamic range of nearly 5 orders of magnitude, an estimated detection limit (SNR = 3) of 3.7 nM (0.16 ppb or 74 fmol injected), and a response variability of 2% or less were observed in the FIA measurements.

"Electrochemical Oxidation Of Polyamines At Diamond Thin-film Electrodes"
Anal. Chem. 1999 Volume 71, Issue 6 Pages 1188-1195
Miles D. Koppang, Małgorzata Witek, John Blau, and Greg M. Swain

Abstract: The oxidation of five polyamines (ethylenediamine, putrescine, cadaverine, spermine, and spermidine) was studied at polycrystalline, boron-doped, diamond thin-film electrodes using cyclic voltammetry and flow injection analysis (FIA) with amperometric detection. Cyclic voltammetry of the polyamines was conducted in pH 10 carbonate buffer. Well-resolved oxidation waves with respect to the background signal were observed, and the current-potential curves exhibited a scan rate dependence characteristic of slow desorption kinetics of the polyamine oxidation product. E1/2s of ~+0.88 V vs. Ag/AgCl were measured for all five polyamines. A mechanism is proposed whereby the polyamine oxidation occurs by oxygen transfer from reactive OH radicals. These radicals are produced during the initial stage of oxygen evolution at the nondiamond carbon impurity sites. These sites are believed to be located primarily at the grain boundaries, isolated from one another by the diamond microcrystallites, although the impurities could also exist as extended defects within the lattice. Stabilization of the polyamine prior to oxidation is achieved through adsorption/complexation of the amine functionality with surface boron dopant atoms, also clustered at the grain boundaries. In general, the FIA results demonstrated that the diamond can be used to effectively detect all five polyamines with a concentration. limit of quantitation of ~1 µM (S/N ≥ 3) and a linear dynamic range from 10^-3 to 10^-6 M (r2 > 0.97). These detector figures of merit were achieved at constant potential without prior derivatization. Lower quality rather than higher quality diamond films are needed for this assay, and the requisite film properties can be introduced by judicious choice of the deposition conditions.

"Aliphatic Polyamine Oxidation Response Variability And Stability At Boron-doped Diamond Thin-film Electrodes As Studied By Flow-injection Analysis"
Anal. Chim. Acta 2001 Volume 440, Issue 2 Pages 119-129
Małgorzata A. Witek and Greg M. Swain

Abstract: Previously it was shown that four different aliphatic polyamines can be quantitatively electrooxidized. at boron-doped diamond thin film electrodes without derivatization or the use of pulsed voltammetric waveforms [Anal. Chem. 71 (1999) 1188; Anal. Chem. 69 (1997) 4041]. The flow injection analysis (FIA-EC) investigation (amperometric detection mode) of cadaverine (CAD), putrescine (PUT), spermine (SPM) and spermidine (SPMD), reported previously [Anal. Chem. 71 (1999) 1188], are updated herein with particular emphasis on the electrode response variability and stability. Most of the measurements were made with a film deposited from a 0.50% methane-to-hydrogen (C/H) volumetric ratio. In general, films deposited with C/H ratios near this value tend to possess the requisite physicochemical properties to support anodic oxygen transfer reactions. The electrode performance was evaluated in terms of the linear dynamic range, limit of quantitation, response variability and response stability. A linear dynamic range from 1.0 muM to 1.0 mM and a limit of quantitation of 1.0 muM or 20 pmol injected (S/N greater than or equal to 3) were found for CAD, PUT, and SPMD. For SPM, a linear dynamic range from 0.32 muM to 1.0 mM and a limit of quantitation of 0.32 muM or 6.4 pmol were observed. The response variability, as low as 2-4%, was observed which is vastly improved over previous results. The improvement was achieved by introducing a 3-6 min delay period between injections. The long-term response stability was good with no evidence for any progressive response attenuation or complete fouling by the reaction product, even though a solid deposit was observed to accumulate on the electrode surface with extended use. The deposit appears to partially reduce the active electrochemical area for polyamine oxidation and to decrease the overpotential for water discharge. Preliminary chromatographic results demonstrated the possibility of separating and detecting the polyamines by a simple reverse-phase scheme at constant applied potential.

"Polycrystalline Diamond Electrodes: Basic Properties And Applications As Amperometric Detectors In Flow Injection Analysis And Liquid Chromatography"
Anal. Chim. Acta 1999 Volume 397, Issue 1-3 Pages 145-161
Michael C. Granger, Jishou Xu, Jerzy W. Strojek and Greg M. Swain

Abstract: Diamond films, fabricated by chemical vapor deposition, provide electrochemists with an entirely new type of carbon electrode that meets the requirements of activity, conductivity, and stability for a wide range of applications. In this manuscript, the basic electrochemical properties of high quality diamond thin-films (3-6 µm thick) are highlighted. The films are polycrystalline, hydrogen terminated and doped with boron (ca. 10(19)-10(20) cm(-3)). Some preliminary results using diamond in amperometric detection schemes, coupled with flow injection analysis and liquid chromatography, are presented for azide and nitrite, chlorpromazine, ascorbic acid and catecholamines. The use of diamond for the voltammetric detection of trace metal ions is also illustrated. The detector figures of merit (e.g., dynamic range, sensitivity, detection limit, response variability and response stability) for diamond are compared with freshly polished glassy carbon. Diamond exhibits as good or superior detector performance for each of these analytes. For example, the detection limit (S/N=3) for chlorpromazine at diamond is 4 nM or 26 pg, and the response variability is 0.3%, while for glassy carbon the detection limit(S/N=3) is 40 nM or 260 pg, and the response variability is 1%. The properties of diamond electrochemical interfaces are far from being fully understood, but the results reported herein portend the favorable possibilities for applications of diamond in electroanalysis.