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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D. Brynn Hibbert

Abbrev:
Hibbert, D.B.
Other Names:
Address:
School of Chemistry, University of New South Wales Sydney, NSW 2052 Australia
Phone:
NA
Fax:
+61-2-9385-4713

Citations 10

"Flow Injection Potentiometry For Enzymatic Assay Of Cholesterol With A Tungsten Electrode Sensor"
Talanta 1999 Volume 49, Issue 3 Pages 639-649
Manihar Situmorang, Peter W. Alexander and D. Brynn Hibbert

Abstract: Flow injection potentiometry (FIP) for the enzymatic determination of cholesterol is reported. The assay utilises a combination of three enzymes: cholesterol esterase (CE), cholesterol oxidase (COD) and peroxidase (POD). The method is developed by the use of a tungsten wire electrode as a sensor vs. Ag/AgCl in conjunction with a redox mediator ferrocyanide. CE converts esterified cholesterol to free cholesterol, which is then oxidized by COD with hydrogen peroxide as product. Ferrocyanide is converted to ferricyanide by hydrogen peroxide, catalyzed by POD, and the tungsten electrode responds to the ratio of ferricyanide to ferrocyanide. Flow injection potentiometry gave well-defined peaks for cholesterol samples with a fast response (30 s). Linear calibration was obtained from 0.05 to 3.0 mM cholesterol, with a slope of 60.2 mV/decade change in cholesterol concentration, and detection limit 0.01 mM cholesterol (S/N = 3). Repeatability was 3% (CV). Interferences from commonly found species were shown to be negligible. The sensor cell is simple to construct, and it was free from surface contamination problems over long periods of use. The application of the sensor for the determination of serum cholesterol was demonstrated.

"Amperometric Detection Of Amines Using Cobalt Electrodes After Separation By Ion-moderated Partition Chromatography"
Talanta 1997 Volume 44, Issue 2 Pages 239-248
A. Hidayata, D. B. Hibberta,* and P. W. Alexanderb

Abstract: Amines were separated by HPLC on an Aminex HPX-72-0 column (30 cm x 7.8 mm i.d.) with 75 mM NaOH as mobile phase (0.75 ml/min) and amperometric detection at 0.4 V vs. Ag/AgCl using a Co working electrode. Results were compared with those obtained using a Cu electrode. FIA experiments were also performed using 75 mM NaOH as carrier (0.75 ml/min). The addition of organic modifier did not improve the results. The RSD n = 10) was 1.3% for 12 nmol methylamine. The electrode response was stable for 3-4 days. Separation of six amines was achieved using the HPLC method with retention time RSD of Calibration graphs were linear for 30 (for benzylamine) to 300 (methylamine) times the limit of detection (6.3 and 0.5 nmol, respectively).
Amines, alkyl Amines, aromatic Amperometry Electrode Method comparison

"Simultaneous Amperometric And Potentiometric Detection Of Sugars, Polyols And Carboxylic Acids In Flow Systems Using Copper Wire Electrodes"
J. Chromatogr. A 1997 Volume 766, Issue 1-2 Pages 27-33
Z. -L Chen and D. B Hibbert*

Abstract: The use of polished Cu wire electrodes (3 cm x 0.5 mm o.d.) for electrochemical detection was evaluated by cyclic voltammetry and FIA with amperometric and potentiometric detection. Sugars and polyols were amperometrically detected at 0.5 V vs. Ag/AgCl in 100 mM NaOH; calibration graphs were linear from 1-1000 µM and detection limits were 2 pmol glycerol, 5 pmol fructose and glucose and 80 pmol ethanol. Carboxylic acids were potentiometrically detected in aqueous solution; calibration graphs were linear from 0.01-1 mM and detection limits were 10 pmol citric acid and 50 pmol acetic acid. The RSD (n = 5) were 2-3% for all analytes. The electrodes were then used in the analysis of a portion (10 µL) of a mixed solution of the analytes by ion-exclusion chromatography on a Bio-RAD HPX-87H column (dimensions not given) at 30°C with water of pH 5.5 as mobile phase (0.5 ml/min). The eluate was initially detected by potentiometry then merged with a flow (0.5 ml/min) of 100 mM NaOH solution prior to amperometric detection (chromatogram shown).
Carboxylic acids Polyols Sugars Glycerol Fructose Glucose Ethanol Citric acid Acetic acid Amperometry HPIC Potentiometry Electrode Column

"A Portable Fill-and-Flow Channel Biosensor With An Electrode To Predict The Effect Of Interferences"
Electroanalysis 2004 Volume 16, Issue 15 Pages 1221-1226
Min Zhao, Ian S. Harding, D. Brynn Hibbert*, J. Justin Gooding

Abstract: A portable fill-and-flow channel biosensor with a predictor electrode is described. The predictor electrode, on the opposite channel wall and upstream of the detector electrode, allows direct evaluation of the current due to interfering species at the detector electrode. A model is developed which shows that the reaction at the upstream predictor electrode has no significant effect on the concentration distribution of the interfering species at the detector electrode. This enables a straightforward correction of the current at the detector electrode and a determination of the analyte concentration. The effect of interference from ascorbic acid in the detection of glucose in samples was efficiently removed by using such a concept. The recovery of glucose from samples containing ascorbic acid was 103% (s=12%, n=3). The approach was also applied to a biosensor for the determination of glucose in red wine samples containing polyphenolic interferents.
Glucose

"The Determination Of Ethanol In Wine By Voltammetry With An Internal Standard"
Electroanalysis 1997 Volume 9, Issue 7 Pages 544-548
Ji Jin Yu, Weiguang Huang, D. Brynn Hibbert*

Abstract: A rapid method for the electroanalysis of ethanol is presented that incorporates flow extraction at room temperature, with voltammetric detection and potassium ferrocyanide as internal standard. in 0.1 M NaOH electrolyte, ethanol was oxidized at a platinum comb-shaped working electrode at -300 mV (vs. a Ag/AgCl reference electrode) and K4Fe(CN)(6) was oxidized at +180 mV. The ratio of the anodic peak currents was Linear with ethanol concentration in the range of 0.1 to 8.0% (v./v.), and the detection limit (calculated as 3s background) was 0.012 % (v./v.) for Osteryoung square wave voltammetry (OSWV) and 0.023 %(v./v.) for cyclic voltammetry (CV). The average extraction efficiency of ethanol from aqueous solutions, at 20±1°C, was 8.5%. The repeatability was in the range of 2.5 to 3.3% RSD (n = 8), and accuracy was in the range of 95.2 to 104.7% for the determination of wine samples. Application to wines compared well with GC and HPLC methods and the nominal ethanol concentration determined by gravimetry. Analytical parameters in CV and OSWV are optimized, and the dependence of the extraction efficiency with temperature and nitrogen gas flow is presented. 20 References
Ethanol Wine Amperometry Voltammetry Electrode Sample preparation Extraction Optimization Method comparison

"Flow Injection, Amperometric Determination Of Ethanol In Wines After Solid-phase Extraction"
Electroanalysis 1997 Volume 9, Issue 7 Pages 541-543
Zuliang Chen, Ji Jin Yu, D. Brynn Hibbert*

Abstract: Wine (0.5 ml) was diluted with water (1 ml) and purified on a Super Clean LC-SAX anion exchange-cartridge by elution with 2 mL water. A portion of the eluate was injected into a stream (0.5 ml/min) of 0.1 M NaOH of a FIA system. Detection was effected with a Ni wire working electrode, a Ag/AgCl reference electrode and a Pt wire counter electrode. A potential of +0.6 V was applied to the working electrode. The detection limit was 1 µM-ethanol. The response was linear up to 1 mM. Recoveries ranged from 100.8-102.9%.
Ethanol Wine Amperometry Electrode Ion exchange Sample preparation Extraction

"Amperometric Flow Injection Analysis Of Organic Thiols And Proteins"
Electroanalysis 1996 Volume 8, Issue 5 Pages 468-472
Achmad Hidayat, D. Brynn Hibbert *, Peter W. Alexander

Abstract: Portions (10 µL) of standard L-cysteine (I) solution was injected into a carrier stream of 100 mM phosphate buffer of pH 3.1 containing 15 µM-Hg(II) [1.5 ml/min] of a flow injection system and detected at a W electrode at -0.24 V vs. Ag/AgCl with a Pt wire auxiliary electrode. The calibration graph was linear over the range 0.25-100 µM-I with a detection limit of 0.25 µM. Silver and iodate ions were observed to interfere. Thiourea (II), glutathione (III), DNA and albumin were similarly detected, and appropriate analytical data are briefly presented. I, II, reduced-III, DL-homocysteine, DL-penicillamine and 3-mercaptopropanoic acid were resolved by HPLC on a Zorbax ODS column (25 cm x 4.6 mm i.d.), aqueous 50 mM 3-chloroacetate/methanol (99:1) of pH 2.3 as mobile phase (0.3 ml/min) and post-column reaction with 50 mM phosphate buffer of pH 2.3 containing 15 µM-Hg(II) (1 ml/min) for amperometric detection as before.
Cysteine Thiols Amperometry HPLC Interferences

"A Tubular Graphite-epoxy Electrode Incorporating Horseradish Peroxidase As A Potentiometric Sensor For Hydrogen Peroxide"
Electroanalysis 1995 Volume 7, Issue 8 Pages 722-725
Zulfikar, D. Brynn Hibbert*, Peter W. Alexander

Abstract: A novel potentiometric peroxidase enzyme sensor based on a tubular graphite-epoxy design is reported for the determination of hydrogen peroxide in an FIA system. The sensor was formed from horseradish peroxidase (40 mg), graphite (240 mg) and epoxy (780 mg). Hydrogen peroxide, injected into pH 7,0.05 M phosphate buffer at 26°C, was determined with a linear slope of 45.6 mV/decade in the concentration range 7.5 x 10^-7 to 5.0 x 10^-5 M. Acceptable reproducibility of 1.2% relative standard deviation was obtained in the flow injection analysis. The advantages of this sensor are low cost, simple electronic circuit design and better selectivity than amperometric sensors and a detection limit comparable with other methods.

"Flow Injection Potentiometry By Poly(vinyl Chloride)-membrane Electrodes With Substituted Azacrown Ionophores For The Determination Of Lead(II) And Mercury(II) Ions"
Anal. Chim. Acta 1998 Volume 372, Issue 3 Pages 387-398
Xinhao Yang, D. Brynn Hibbert* and Peter W. Alexander

Abstract: A flow cell with a poly(vinyl chloride) (PVC) neutral-ionophore liq.-membrane ion-selective electrode was developed for flow injection potentiometry (FIP). The flow system was optimized and five substituted azacrown ethers: 7,16-dithenoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTODC), 7,16-di-(2-thiopheneacetyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTAODC), 7,16-dithenyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTDC), 1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TC) and 4,7,13,16-tetrathenoyl-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TTOTC) synthesized and studied as the ionophores in Pb2+ (DTAODC, TTOTC) and Hg2+ (DTDC, DTODC, TC, TTOTC) selective electrodes. The short contact times between analyte and ionophore in FIP allow the measurement of a strongly complexing ion such as Hg2+ that sats. the electrodes in batch anal., or in continuous-flow anal. that comes to a steady state. For the mercury-selective electrodes with ionophores with amide functional groups (TTOTC and DTODC) a carrier of 10 mM potassium nitrate increases the speed of response and recovery to baseline. The linear calibration range for a DTAODC lead-selective electrode was pPb = 2.0 to 5.0 with a slope of 32.5 mV decade-1 and for a TTOTC mercury-selective electrode, pHg = 3.0 to 5.5 with a slope of 28.4 mV decade-1. Highly reproducible measurements were obtained (relative standard deviation <2%) at a flow rate of 3.0 mL min-1 giving a typical throughput of 40 samples h-1 for Pb2+ and 30 samples h-1 for Hg2+.
Lead(2+) Mercury(II) Potentiometry Electrode Electrode Electrode Electrode Optimization Apparatus Detector

"Simultaneous Amperometric And Potentiometric Detection Of Inorganic Anions In Flow Systems Using Platinum And Silver/silver Chloride Electrodes"
Anal. Chim. Acta 1997 Volume 350, Issue 1-2 Pages 1-6
Z. Chen and D. B. Hibbert*

Abstract: Platinum and silver/silver chloride electrodes were evaluated for electrochemical detection (amperometry and potentiometry, respectively) of inorganic anions in flow systems. In flow injection analysis, a linear response over three decades and detection limit of 1 x 10^-7 M for I- and NO-2 were obtained at an applied potential of +0.9 V (vs. Ag/AgCl) in 30 mM phosphate buffer at pH 3.0 as carrier. A silver/silver chloride electrode responded potentiometrically to halides and pseudo-halides in this buffer with a detection limit of 1 x 10^-5 M. The detector, which included both detection systems, was coupled with ion chromatography. Following separation by anion-exchange chromatography with 40 mM phosphate buffer at pH 4.5 as eluent, Cl-, Br-, I-, SCN-, and S2O2-3 were determined potentiometrically with a detection limit of 1 x 10^-5 M, and, simultaneously, NO-2, Br-, I-, and SCN- were determined amperometrically with a detection limit of 1 x 10^-6 M. Ioninteraction chromatography with an eluent of 20 mM phosphate at pH 5.0 containing 5 mM tetrabutylammonium hydroxide separated and detected Br-, NO-2 and SCN-.
Iodide Nitrite Chloride Bromide Thiocyanate ion Sulfite Potentiometry Amperometry Electrode Electrode Simultaneous analysis Buffer