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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Soo Beng Khoo

Abbrev:
Khoo, S.B.
Other Names:
Soobeng Khoo
Address:
Department of Chemistry, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
Phone:
+65-874-2919
Fax:
+65-779-1691

Citations 8

"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.

"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.

"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

"Differential Pulse Voltammetric Determination Of Trace Te(IV) At A Poly(3,3-diaminobenzidine) Film Modified Gold Electrode In Flow Systems"
Anal. Chim. Acta 2002 Volume 453, Issue 2 Pages 209-220
Soo Beng Khoo and Ruidong Ye

Abstract: Electropolymerization of 3,3-diaminobenzidine on a gold surface gave an adherent, stable film of poly(3,3-diaminobenzidine) (PDAB). This polymer film retained the complexational functionalities of its monomer, demonstrating pre-concentration abilities for several ions, including Se(IV) and Te(IV). In particular, in this work, continuous flow and flow injection methods were developed for the sensitive and selective determination of Te(IV). The optimized method for the continuous flow mode had a detection limit of 5.6 x 10^-9 mol L-1 for 10 min pre-concentration. Typical relative standard deviations for six consecutive determinations were 1.82 and 2.56% for Te(IV) concentrations of 1.0 x 10^-6 and 5.0 x 10^-8 mol l-1, respectively (10 min pre-concentration). The method was applied to the determination of Te(IV) in real samples.

"Electrocatalytic Oxidation Of H2O2 At An Oxycobalt Film-modified Glassy-carbon Electrode For Fermentation Monitoring"
Anal. Chim. Acta 1997 Volume 351, Issue 1-3 Pages 133-142
Soo Beng Khooa,*, M. G. S. Yapc, b, Yu Liang Huangb and Sixuan Guoa

Abstract: Glassy carbon electrodes coated with thin oxymetallic films of Co(II), Fe(II), Ni(II), Pb(II), Ce(III), Cr(III), Tl(I) and Mn(II) were investigated for the presence of electrocatalytic effect towards H2O2 oxidation. Of these, Co(II), Ni(II), Pb(II), Ce(III) and Mn(II) were found to exhibit such an effect in alkaline medium, with Co(II) showing the strongest effect. Further studies with the Co(II) modified glassy carbon electrode as amperometric detector, in the wall-jet configuration, for flow injection analysis (FIA) demonstrated that only a low operating potential of +0.175 V (vs. Ag/AgCl, saturated KCl) was needed for good sensitivity. For flow injection analysis, linearity of H2O2 calibration was found from 5.00 x 10^-8 to 0.10 M and the detection limit was 5.0 x 10^-9 M (S/N=3). The electrode showed good stability (at least two weeks operation) and can be usefully applied to glucose determination in the fermentation broths without interferences. 30 References
Glucose Hydrogen peroxide Fermentation broth Electrode Electrode Interferences Sensitivity Process monitoring

"Characterization And Application Of An Online Flow Injection Analysis/wall-jet Electrode System For Glucose Monitoring During Fermentation"
Anal. Chim. Acta 1995 Volume 317, Issue 1-3 Pages 223-232
Yu Liang Huanga, Titus J. Foellmera, Koon Chye Anga, Soo Beng Khoob,* and Miranda G. S. Yapa

Abstract: An online system for glucose monitoring during fermentation was developed. The system employed flow injection analysis coupled with a wall-jet electrode. Glucose was converted enzymatically in a tubular reactor packed with controlled pore glass beads containing immobilized glucose oxidase. The hydrogen peroxide produced was detected amperometrically. A filtration/sampling module operated by a peristaltic pump enabled sample withdrawal from the fermenter. The system was interfaced to a programmable language controller which was in turn linked to a microcomputer. The dual injection valve of the flow system was operated in a novel configuration to achieve sample dilution, by dispersion, and standardization simultaneously. The developed system was characterized for dilution factor, stability and linearity of response. After conditioning of the reactor, sample peak heights were found to have a precision of 1.07% (RSD, 25 determinations) when the glucose concentration was 1.32 g l-1. Under the conditions studied, linear response to glucose concentration from 0.062 to 4.0 g L-1 was obtained. Sample throughput was about 7 per hour. Interferences from the fermentation media were negligible after filtration through the sampling module and dilution. The online system was applied to glucose monitoring during E. coli fermentation. Good results were obtained as shown by the high cell density (OD6-00 nm = 168 in 9 h fermentation), constant specific growth rate (µ= 0.66) and lower acetate accumulation (less than 2 g L-1 when OD-600 nm was over 50). (18 References)
Glucose Fermentation broth Electrode Controlled pore glass Immobilized enzyme Interferences Apparatus Detector Computer Process monitoring

"Determination Of Trace Tin In Flow Systems At An Epoxy-carbon Powder-8-hydroxyquinoline Composite Electrode"
Analyst 2000 Volume 125, Issue 5 Pages 895-902
Soo Beng Khoo and Ruidong Ye

Abstract: An epoxy-carbon powder composite electrode bulk modified with 8-hydroxyquinoline was fabricated for the continuous flow and flow injection anodic differential pulse voltammetric determinations of Sn(II) after open circuit pre-concentration. Factors affecting Sn(II) determination were systematically investigated and an optimized procedure was developed. Under the optimized conditions for the continuous flow system with 10 min accumulation, the calibration plot was linear from 5.00 x 10^-9 to 1.00 x 10^-6 M and a detection limit of 4.6 x 10^-10 M (0.055 ppb, S/N = 3) was found. For six consecutive differential pulse stripping experiments each of Sn(II) concentrations of 5.00 x 10^-9, 5.00 x 10^-8 and 5.00 x 10^-7 M (10 min accumulations), relative standard deviations of 9.68, 7.45 and 3.38%, respectively, were obtained. For the flow injection mode, a detection limit of 5.4 ng (500 µl injection of 0.91 x 10^-8 M, S/N = 3) was achieved. Selected metal ions and other substances were investigated for interferences. The developed method was tested with a spiked United States Environmental Protection Agency water quality control sample (USEPA WP 386) and then applied to the determinations of tin in human hair, canned fruit juice and spiked sea-water samples.
Preconcentration

"Cathodic Stripping Voltammetric Determination Of Ultratrace Gold(III) At A Bulk Modified Epoxy-graphite Tube Composite Electrode In Flow Systems"
Analyst 1999 Volume 124, Issue 3 Pages 353-360
Ruidong Ye and Soo Beng Khoo

Abstract: An epoxy-impregnated graphite tube composite electrode bulk; modified with 2-mercaptobenzoxazole was fabricated and employed for the determination of gold. A differential-pulse cathodic stripping procedure in conjunction with either continuous flow or flow injection was developed. Both open and closed circuit accumulation of Au(III) were investigated. The addition of Rhodamine 6G to the accumulation medium enhanced the sensitivity. Factors influencing the analysis were optimized. For continuous flow, precisions were 6.33% [relative standard deviation, la = 6, 5.00 x 10^-8 M Au(III), accumulation 10 min, open circuit] and 7.06% [n = 6, 1.00 x 10^-9 M Au(III), accumulation 10 min, closed circuit]. The detection limits (S/N = 3) were 6.7 x 10^-9 and 1.9 x 10^-10 M Au(III) for Open and closed circuit accumulations, respectively, with 10 min accumulation. For flow injection under similar conditions, the detection limits were 3.1 x 10^-7 M Au(III) (open circuit, injection volume 500 µl, 30.5 ng injected) and 2.9 x 10^-9 hi (closed circuit, injection volume 500 µl, 0.29 ng injected). Selected metal ions and other inorganic and organic substances were examined for interferences. The developed method was applied to a certified water sample (US EPA WP 386), a sea-water sample and a pin-connector sample.