Biomedical subjects

C Terashima

Publications and source records attributed to C Terashima.

6 recordsLinked to original sources

PubMed2003

Gradient liquid chromatography of leucine-enkephalin peptide and its metabolites with electrochemical detection using highly boron-doped diamond electrode.

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 microM 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.

Boron↗

PubMed2003

Direct electrochemical oxidation of disulfides at anodically pretreated boron-doped diamond electrodes.

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.

Journal Article↗

PubMed2002

Electrochemical detection of carbamate pesticides at conductive diamond electrodes.

Conductive boron-doped diamond thin-film electrodes were used for the electrochemical detection of selected N-methylcarbamate pesticides (carbaryl, carbofuran, methyl 2-benzimidazolecarbamate, bendiocarb) after liquid chromatographic separation. Two kinds of detection methods were adopted in this study. In the first method, a direct detection of underivatized pesticides was carried out at an operating potential of 1.45 V versus Ag/AgCl, which resulted in the detection limits of 5-20 ng/mL (or 5-20 ppb) with S/N = 2 due to the low background current and wide potential window of the diamond electrode. In the second method, the detection limits were improved by subjecting the pesticide samples to alkaline hydrolysis in a separate step prior to injection. The phenolic derivatives obtained by alkaline hydrolysis oxidize at a relatively lower potential (0.9 V vs Ag/AgCl), which increases the sensitivity drastically. The advantage of the diamond electrode for the detection of phenolic derivatives is that it offers excellent stability in comparison to other electrodes. This method gives the detection limits of 0.6-1 ng/mL (or 0.6-1 ppb), which are well below the maximum residue levels allowed for carbaryl, carbofuran, and bendiocarb. While the lowest detection limits (LOD) obtained by the direct detection of pesticides are comparable to the those reported by the well-established HPLC-fluorescence, the LODs of the alkaline hydrolysis method are found to be even lower than the reported limits. On-line reactivation of the diamond electrode surface was shown to be possible by an anodic treatment of the electrode at approximately 3 V for 30 min in case of electrode fouling, which may occur after a prolonged use. Such a treatment damages the glassy carbon (GC) and metal electrodes, while the diamond electrode remains stable. These results suggest that the diamond electrode is superior to the other previously used electrodes such as GC and Kelgraf type for highly sensitive and stable detection of carbamate pesticides.

Carbamates↗

PubMed2002

Electrochemical oxidation of chlorophenols at a boron-doped diamond electrode and their determination by high-performance liquid chromatography with amperometric detection.

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 microM. By coupling with the column-switching technique, which enabled on-line preconcentration (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.

Boron↗

PubMed2002

The electrochemical oxidation of homocysteine at boron-doped diamond electrodes with application to HPLC amperometric detection.

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.

Boron↗

PubMed2001

New micro-flow pumping system for liquid chromatography.

This paper deals with the development of practical approaches to a new liquid-delivery system for capillary liquid chromatography. Under different chromatographic conditions, the factors affecting liquid-delivery performance are theoretically described, and the new liquid-delivery system without any splitter is evaluated with its flow-rate accuracy and precision using a variety of solvents. The experimental results demonstrate that the liquid-delivery system is capable of generating accurate, reproducible and conditions-independent micro- and nano-flows.

Chromatography, High Pressure Liquid↗