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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Akira Fujishima

Abbrev:
Fujishima, A.
Other Names:
Address:
Department of Applied Chemistry, School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Phone:
+81-3-3812-2111
Fax:
+81-3-3812-6227

Citations 12

"Tyrosinase-modified Boron-doped Diamond Electrodes For The Determination Of Phenol Derivatives"
J. Electroanal. Chem. 2002 Volume 523, Issue 1-2 Pages 86-92
Hideo Notsu, Tetsu Tatsuma and Akira Fujishima

Abstract: Highly boron-doped diamond (BDD) electrodes were modified covalently with tyrosinase for the determination of estrogenic phenol derivatives, BDD was anodically polarized for the introduction of hydroxyl groups onto its surface, then treated with (3-aminopropyl)triethoxysilane and finally coated with a tyrosinase film cross-linked with glutaraldehyde. The modified electrodes responded amperometrically to phenol derivatives including estrogenic derivatives, bisphenol-A and 17β-estradiol. at -0.3 V versus Ag/AgCl. Interference from direct reduction of oxygen at the electrode surface was almost negligible because the overpotential for the oxygen reduction at BDD was greater than those for most conventional electrode materials. The electrodes were applied to a flow injection system. and the lower detection limit for bisphenol-A was 10 (6) M. The stability and proper sampling interval were also studied. (C) 2002 Elsevier Science Ltd. All rights reserved.

"Electrochemical Detection Of Tricyclic Antidepressant Drugs By HPLC Using Highly Boron-doped Diamond Electrodes"
J. Electroanal. Chem. 2002 Volume 521, Issue 1-2 Pages 117-126
T. A. Ivandini, B. V. Sarada, C. Terashima, T. N. Rao, D. A. Tryk, H. Ishiguro, Y. Kubota and A. Fujishima

Abstract: Boron-doped diamond (BDD) electrodes have been examined for the electrochemical detection of six tricyclic antidepressant drugs (TCAs): iniipramine, desipramine, clomipramine, amitriptyline, nortriptyline, and doxepin. Cyclic voltammetry, flow injection analysis (FIA) and HPLC with electrochemical detection have been used to study the oxidation reactions and to detect the TCAs. At diamond electrodes, well-defined and highly reproducible voltammograms were obtained for all six drugs with a signal to background (S/B) ratio about 2-4 times greater than those at glassy carbon electrodes. Diamond is the first electrode material to show well-defined voltammograms for nortriptyline due to its wide potential window. In the FIA-mode, at an operation potential of 0.85 V versus Ag AgCl, diamond exhibited a background current of 7 nA with rapid stabilization (15 min) conversely to the case of GC, which appeared to stabilize after I h, but again increased thereafter. The analytical peaks of HPLC for the TCAs were well resolved. Linear calibration curves were linear over the ranges from 0.05 to 100 muM. The limits of detection (S/N = 3) were 3 nM for iniipramine and desipramine, 0.5 nM for clomiprarnine, 163 nM amitriptyline, 1080 nM for nortriptyline and 92 nM for doxepin. The electrodes have shown reproducible results over several days of analysis. This method has been applied for the determination of imipramine and desipramme in plasma samples. The BDD surface was reproducible with no adsorption of blood components during plasma analysis. This work shows the promising use of diamond as an amperometric detector in HPLC, especially for TCA analysis. (C) 2002 Published by Elsevier Science B.V.

"Surface Carbonyl Groups On Oxidized Diamond Electrodes"
J. Electroanal. Chem. 2000 Volume 492, Issue 1 Pages 31-37
Hideo Notsu, Ichizo Yagi, Tetsu Tatsuma, Donald A. Tryk and Akira Fujishima

Abstract: Oxygen-containing functional groups can be introduced onto the surface of polycrystalline boron-doped diamond electrodes by either anodic polarization or oxygen plasma treatment. Of these, the carbonyl groups are of particular interest and can be studied specifically by means of specific chemical modification with dinitrophenylhydrazine (DNPH). The modification of the surface carbonyl groups with DNPH retards the Fe2+/3+ redox reaction, which is known to be catalyzed by carbonyl groups. Anodic polarization generated a larger number of carbonyl groups per unit area that were reactive with DNPH than that generated by oxygen plasma treatment. The molar ratio of the DNPH-reactive carbonyl groups to the total of all types of oxygen atoms could be as high as 5% for electrochemically oxidized diamond surfaces. This value is reasonable in view of steric limitations. The total number of carbonyl groups per unit area introduced by oxygen plasma treatment was probably larger than that introduced by anodic polarization, but the number that can react with DNPH is lower due to disordering by energetic oxygen ions.

"Electroanalytical Study Of Sulfa Drugs At Diamond Electrodes And Their Determination By HPLC With Amperometric Detection"
J. Electroanal. Chem. 2000 Volume 491, Issue 1-2 Pages 175-181
Tata N. Rao, B. V. Sarada, D. A. Tryk and A. Fujishima

Abstract: Conductive boron-doped diamond thin film electrodes were examined for the electroanalysis of three sulfa drugs, sulfadiazine, sulfamerazine and sulfamethazine. Cyclic voltammetry, flow injection analysis and liquid chromatography with electrochemical detection were used to study the oxidation reactions. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for all three drugs with a signal to background (S/B) ratio of a factor of ten greater than that obtained at two types of freshly polished glassy carbon (GC) electrodes. Diamond exhibited a highly reproducible amperometric response, with a peak variation of similar to 5%, even at a concentration of 100 nM. A detection limit of 50 nM and a linear dynamic range of three orders of magnitude were obtained. No fouling of the electrode was observed within the experimental period of several hours. A rapid stabilization of the background current is achieved, within 10 min after the application of the operating potential under flow conditions, unlike the case of GC electrodes, which requires more than 30 min for reasonable stabilization. We have demonstrated the application of the diamond electrode for the simple and sensitive amperometric detection of the sulfa drugs in a standard mixture after their separation with reverse-phase HPLC to produce chromatograms with a flat baseline and high reproducibility, even at concentrations as low as 100 nM.

"Gradient Liquid Chromatography Of Leucine-enkephalin Peptide And Its Metabolites With Electrochemical Detection Using Highly Boron-doped Diamond Electrode"
J. Chromatogr. B 2003 Volume 791, Issue 1-2 Pages 63-72
T. A. Ivandini, B. V. Sarada, C. Terashima, T. N. Rao, D. A Tryk, H. Ishiguro, Y. Kubota and A. Fujishima

Abstract: Boron-doped diamond thin film (BDD) electrodes have been used to study the oxidation reactions and to detect leucine-enkephalinamide (LEA) and its metabolites, tyrosine (T), tyrosyl-alanine (TA), tyrosyl-alanine-glycine (TAG) and leucine-enkephalin (LE) using cyclic voltammetry (CV), flow-injection analysis (FIA), and gradient liquid chromatography (LC) with amperometric detection. At diamond electrodes, well-defined and highly reproducible cyclic voltammograms were obtained with signal-to-background (S/B) ratios 5-10 times higher than those observed for glassy carbon (GC) electrodes. The analytical peaks of LC for LEA and its metabolites were well resolved. No deactivation of BDD electrodes was found after several experiments with standard as well as plasma samples, indicating high stability of the electrode. Calibration curves were linear over a wide range from 0.06 to 30 µM with regression coefficients of 0.999 for all compounds. The limits of detection obtained based on a signal-to-noise ratio of 3:1 were 3, 2.2, 2.7, 20 and 11 nM for T, TA, TAG, LE and LEA, respectively. These values were at least one order lower than those obtained at GC electrodes, which has given limits of detection of 22.88, 20.64, 89.57, 116.04 and 75.67 for T, TA, TAG, LE and LEA, respectively. Application of this method to real samples was demonstrated and validated using rabbit serum samples. This work shows the promising use of conducting diamond as an amperometric detector in gradient LC, especially for the analysis of enkephalinamide and its metabolites.

"Metal-modified Diamond Electrode As An Electrochemical Detector For Glucose"
Chem. Lett. 2001 Volume 30, Issue 2 Pages 144-145
Ryuji Uchikado, Tata N. Rao, Donald A. Tryk and Akira Fujishima

Abstract: Nickel- and copper-modified diamond electrodes were fabricated in view of their application for carbohydrate detection. Both electrodes produced well-defined and reproducible voltammograms for I mM glucose in alkaline media. These electrodes exhibited excellent electrochemical stability with low background current for at least one week in a flow injection analysis system, indicating good adherence of the metal clusters to diamond. These results indicate the promising use of nickel-and copper-modified diamond electrodes for the detection of carbohydrates and amino acids.

"Electrochemical Detection Of Serotonin Using Conductive Diamond Electrodes"
Chem. Lett. 1999 Volume 28, Issue 11 Pages 1213-1214
Bulusu V. Sarada, Tata N. Rao, Donald A. Tryk, and Akira Fujishima

Abstract: The electrochemical detection of serotonin with highly B-doped diamond thin film electrodes was studied using flow injection analysis (FIA) with amperometric detection. The voltammetric behavior of diamond indicated low background current and a low tendency to adsorb the oxidative products on the electrode surface, in comparison to the glassy C electrode. An experimental amperometric detection limit of 10 nM (0.2 pmol) was obtained for the FIA technique, demonstrating that diamond is a stable and sensitive electrode for serotonin determination.

"Detection Of Ascorbic Acid In An Ethanol–Water Mixed Solution On A Conductive Diamond Electrode"
Bull. Chem. Soc. Jpn. 2003 Volume 76, Issue 5 Pages 927-933
Masaharu Komatsu and Akira Fujishima

Abstract: Conductive boron-doped diamond thin-film electrodes have been shown to be highly suitable as electrochemical detectors in flow injection analysis (FIA) due to the lack of electrode deactivation due to fouling and the ability to withstand highly positive electrochemical potentials. In the present work, a diamond electrode was applied to the detection of ascorbic acid (AA) in an alcohol-water mixed solution. During FIA of AA in an ethanol (EtOH)-water solution including 0.1 M NaClO4, the interference from EtOH oxidation that would have been observed with a Pt electrode was avoided, and the amperometric response for AA was observed with the use of a conductive diamond as the electrode material. Moreover, The detection limit for AA that could be observed was lower than that for a glassy carbon electrode, because diamond exhibits a lower background current, smaller background noise, and smaller injection noise. These findings suggest that the diamond electrode may be applied in the detection of other redox-active impurities and added substances in alcohol or alcohol-water solutions, such as chlorophyll, nicotinamide, caffeine, riboflavin, and dl-α-tocopherol.
Ascorbic acid Electrode Interferences

"Direct Electrochemical Oxidation Of Disulfides At Anodically Pretreated Boron-Doped Diamond Electrodes"
Anal. Chem. 2003 Volume 75, Issue 7 Pages 1564-1572
C. Terashima, Tata N. Rao, B. V. Sarada, Y. Kubota and A. Fujishima

Abstract: Anodically oxidized diamond electrodes have been used to oxidize disulfides, thiols, and methionine in aqueous acidic media and tested for amperometric detection of these compounds after chromatographic separation. Cyclic voltammetric signals for 1 mM glutathione disulfide (GSSG) were observed at 1.39 and 1.84 V vs SCE, the values being less positive than those of its as-deposited counterpart as well as glassy carbon electrode. The voltammetric and chronocoulometric results have indicated the high stability of the electrode with negligible adsorption. A positive shift in the peak potential with increasing pH indicated the attractive electrostatic interaction between the anodically oxidized diamond surface and the positively charged GSSG in acidic media that promoted its analytical performance. The results of the electrolysis experiments of disulfides and thiols showed that the oxidation reaction mechanism of glutathione (GSH) and GSSG involves oxygen transfer. Following separation by liquid chromatography (LC), the determination of both GSH and GSSG in rat whole blood was achieved at a constant potential (1.50 V vs Ag/AgCl), and the limits of detection for GSH and GSSG were found to be 1.4 nM (0.028 pmol) and 1.9 nM (0.037 pmol) with a linear calibration range up to 0.25 mM. These detection limits were much lower than those reported for the amperometry using Bi-PbO2 electrodes and LC-mass spectrometry, and the LC method using diamond electrodes were comparable with enzymatic assay in real sample analysis. The high response stability and reproducibility together with the possibility of regeneration of the electrode surface by on-line anodic treatment at 3 V for 30 min further support the applicability of anodically pretreated diamond for amperometric detection of disulfides.

"Electrochemical Oxidation Of Chlorophenols At A Boron-doped Diamond Electrode And Their Determination By High-performance Liquid Chromatography With Amperometric Detection"
Anal. Chem. 2002 Volume 74, Issue 4 Pages 895-902
C. Terashima, Tata N. Rao, B. V. Sarada, D. A. Tryk, and A. Fujishima

Abstract: Anodically pretreated. diamond electrodes have been used for the detection of chlorophenols (CPs) in environmental water samples after high-performance liquid chromatographic (HPLC separation. The anodization of as-deposited boron-doped polycrystalline diamond thin-film electrodes has enabled the stable determination of phenols over a wide concentration range. Prior to the HPLC analysis, a comparative study with ordinary glassy carbon, as-deposited diamond, and anodized diamond was made to examine the oxidative behavior of phenols by cyclic voltammety and flow injection analysis with amperometric detection. At anodized diamond electrodes, reproducible, well-defined cyclic voltammograms were obtained even at high CP concentration (5 mM), due to a low proclivity for adsorption of the oxidation products on the surface. In addition, after prolonged use, the partially deactivated diamond could be reactivated on line by applying a highly anodic potential (2.64 Vvs SCE) for 4 min, which enabled the destruction of the electrodeposited polymer deposits. Hydroxyl radicals produced by the high applied potential, in which oxygen evolution occurs, are believed to be responsible for the oxidation of the passivating layer on the surface. When coupled with flow injection analysis (FIA), anodized diamond exhibited excellent stability, with a response variability of 2.3% (n = 100), for the oxidation of a high concentration (5 mM) of chlorophenol. In contrast, glassy carbon exhibited a response variability of 39.1%. After 100 injections, the relative peak intensity, for diamond decreased by 10%, while a drastic decrease of 70% was observed for glassy carbon. The detection limit obtained in the FIA mode for 2,4-dichlorophenol was found to be 20 nM (S/N = 3), with a linear dynamic range up to 100 muM. By coupling with the column-switching technique, which enabled on-line pre-concentration (50 times), the, detection limit was lowered to 0.4 nM (S/N = 3). By use of this technique, anodized diamond electrodes were demonstrated for the analysis of CPs in drainwater that was condensed from the flue gas of waste incinerators.

"Electrochemical Oxidation Of Histamine And Serotonin At Highly Boron Doped Diamond Electrodes"
Anal. Chem. 2000 Volume 72, Issue 7 Pages 1632-1638
B. V. Sarada, Tata N. Rao, D. A. Tryk, and A. Fujishima

Abstract: The electrochemistry of histamine and serotonin in neutral aqueous media (pH 7.2) was investigated using polycrystalline, boron-doped diamond thin-film electrodes. Cyclic voltammetry, hydrodynamic voltammetry, and flow injection analysis (FIA) with amperometric detection were used to study the oxidation reactions. Comparison experiments were carried out using polished glassy carbon (GC) electrodes. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for histamine with a peak potential at 1.40 V vs SCE. The voltammetric signal-to-background ratios obtained at diamond were 1 order of magnitude higher than those obtained for GC electrodes at and above 100 M analyte concentrations. A linear dynamic range of 3-4 orders of magnitude and a detection limit of 1 M were observed in the voltammetric measurements. Well-defined sweep rate-dependent voltammograms were also obtained for 5-hydroxytryptamine (5-HT). The characteristics of the voltammogram indicated lack of adsorption of its oxidation products on the surface. No fouling or deactivation of the electrode was observed within the experimental time of several hours. A detection limit of 0.5 M (signal-to-noise ratio 13.8) for histamine was obtained by use of the FIA technique with a diamond electrode. A remarkably low detection limit (10 nM) was obtained for 5-HT on diamond by the same method. Diamond electrodes exhibited a linear dynamic range from 10 nM to 100 M for 5-HT determination and a range of 0.5-100 M for histamine determination. The FIA response was very reproducible from film to film, and the response variability was below 7% at the actual detection limits.

"The Electrochemical Oxidation Of Homocysteine At Boron-doped Diamond Electrodes With Application To HPLC Amperometric Detection"
Analyst 2002 Volume 127, Issue 9 Pages 1164-1168
O. Chailapakul, W. Siangproh, B. V. Sarada, C. Terashima, Tata N. Rao, D. A. Tryk and A. Fujishima

Abstract: The electrochemical oxidation of homocysteine was studied at as-deposited and anodized (oxidized) boron-doped diamond (BDD) thin film electrodes with cyclic voltammetry, flow injection analysis and high-pressure liquid chromatography with amperometric detection. At anodized boron-doped diamond electrodes, highly reproducible, well-defined cyclic voltammograms for homocysteine oxidation were obtained in acidic media, while as-deposited diamond did not provide a detectable signal. In alkaline media, however, the oxidation response was obtained both at as-deposited and anodized diamond electrodes. The potential sweep rate dependence of homocysteine oxidation (peak currents for 1 mM homocysteine linearly proportional to v(1/2), within the range of 0.01 to 0.3 V s-1) indicates that the oxidation involves a diffusing species, with negligible adsorption on the BDD surface at this concentration. In the flow system, BDD exhibited a highly reproducible amperometric response, with a peak variation less than 2%. An extremely low detection limit (1 nM) was obtained at 1.6 V vs. Ag/AgCl. In addition, the determination of homocysteine in a standard mixture with aminothiols and disulfide compounds by means of isocratic reverse-phase HPLC with amperometric detection at diamond electrodes has been investigated. The results showed excellent separation, with a detection limit of 1 pmol and a linear range of three orders of magnitude.