Voltammetry of dihydroxyphenylalanine ( l-DOPA) using a Nafion-coated carbon fibre ultramicroelectrode array

Fabrication of the graphite based polymer composite electrodes and their application to the stripping analysis is described. The electrode was prepared by filling and extruding the styrene-acrylonitrile copolymer (SA) with graphite powder, which shows significant improvement in signal to noise ratio in comparison with a conventional glassy carbon electrode especially at the anodic potential range. It is demonstrated that the electrodes are well suited for the determination of trace manganese in aqueous solution by cathodic stripping voltammetry (CSV). This method involves a preelectrolysis step whereby the trace Mn(II) was anodically oxidized to Mn(IV) on an electrode surface in an acetate ammonium buffer (pH 9), followed by cathodic stripping technique with a square-wave voltammetric mode. The peak response was characterized with respect to pH, preelectrolysis potential, preelectrolysis time, possible interference, supporting electrolytes, etc. Under the optimal conditions, the stripping peak height linearly increased with the concentration of manganese in the range of 0.2–10 µg/L. The sensitivity and the resolution of the proposed method are obviously better than that of results obtained with the conventional glassy carbon electrode.

Electro-oxidation of herbicide halosulfuron methyl on glassy carbon electrode and applications

A square-wave anodic stripping voltammetry (SWASV) for the determination of trace amounts of hexavalent chromium Cr(VI) at a graphite/styrene-acrylonitrile (Graphite-SAN) copolymer composite electrode is described. This method involves a preconcentration step whereby the trace Cr(VI) was cathodically reduced to Cr(III) on an electrode surface in an acetate buffer (pH 5), followed by an anodic stripping technique with a square-wave voltammetric mode. It has been shown that the analytical sensitivity is significantly improved at the Graphite-SAN copolymer composite electrode in comparison with the conventional glassy carbon electrode, due to the strong interaction between Cr(III) and the nitrile end group of the SAN copolymer. The SWASV response was characterized with respect to the pH, deposition potential, possible interferences, etc. Under the optimal conditions, the stripping peak height linearly increased with the concentration of Cr(VI) in a range from 0 to 150 ng mL-1 with a correlation coefficient of 0.997, and a detection limit of 4.2 ng mL-1 was achieved based on signal-to-noise ratio of about 3. The Graphite-SAN composite electrode exhibited some interesting advantages, such as high mechanical rigid, easy surface renewable, higher sensitivity and better peak resolution in comparison with the results at conventional glassy carbon electrodes. They have been applied to the determination of Cr(VI) in real water samples with satisfactory recoveries.

Dissolution of partially immersed nickel during in situ oxidation in molten carbonate: cyclic, stripping and square wave voltammetry measurements

Preparation and characterization of a multi-cylinder microelectrode coupled with a conventional glassy carbon electrode and its application to the detection of dopamine

Determination of lorazepam in human urine by adsorptive stripping voltammetry

Synergistic effect of ninhydrin and iodide ions during electrodeposition of zinc at steel electrodes

Electrochemical oxidation behavior of hydrochlorothiazide on a glassy carbon electrode and its voltammetric determination in pharmaceutical formulations and biological fluids

The focus of the present work is to develop and optimize an electrochemical laccase-based biosensor for the determination of 3,4-dihydroxyphenyl-alanine, also known as L-DOPA. The biosensor was assembled on a conventional glassy carbon electrode, the surface of which was covered with laccase enzyme retained under a thin Nafion™ membrane. The enzymes used for this purpose were isolated and purified from the white-rot basidiomycetes (Trametes sp.) Trametes pubescens and Trametes versicolor. Although biochemically similar, the two enzymes demonstrated some differences in their affinity not only using 3,4-dihydroxyphenyl-L-alanine as enzyme substrate, but also when catecholamines such as dopamine and L-epinephrine were used. A range of electrochemical techniques were used for the study, such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Experiments were performed using buffers with different pH and applying various substrate concentrations. Activity and sensitivity of the two alternative laccase – based biosensors were compared by means of chronoamperometry. The biosensor produced on the basis of Trametes pubescens laccase, operating in citrate buffer with pH 4 proved to be more suitable than the one based on laccase purified from Trametes versicolor for biosensing L-DOPA.

Preparation and characterization of fullerene-doped low-temperature glassy carbon

Films of vertically aligned multi-walled carbon nanotubes (MWCNT) were selectively synthesized on silicon dioxide substrate by catalytic chemical vapor deposition using either benzene or acetonitrile as carbon source and ferrocene (1% w/w) as catalyst. The MWCNT were extensively characterized by using scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy. In order to examine the prospective application of the fabricated MWCNT films for the detection of electro-active compounds in organic solvent media, electrochemical studies of the oxidation of cobaltocene (CoCp2) to cobaltocenium cation (CoCp 2 + ) (Cp = cyclopentadienyl anion) in acetonitrile were performed on these films. For this purpose, cyclic voltammetry and electrochemical impedance spectroscopy were employed. The electrochemical parameters for the CoCp 2 +/0 couple in acetonitrile were derived and compared with those obtained using a conventional glassy carbon electrode. The results demonstrate that the synthesized MWCNT films are promising electrode materials for the electrochemical detection of electro-active species in organic solvents. The MWCNT film formed upon decay of benzene has higher capacitance, less Warburg impedance, and less charge transfer resistance, and consequently it provides faster electron transfer kinetics.

A rapid electrochemical procedure for the determination of dipyrone was successfully developed at a carbon nanotube modified graphite-epoxy resin composite (GrEC) electrode. The composite electrode was used as support on which multi-walled carbon nanotubes (MWCNT) were immobilised by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide together with N-hydroxysuccinimide (EDC-NHS) in a chitosan (Chit) matrix. The electrochemical behaviour of dipyrone at this electrode in different buffer electrolytes with pH values between 5.0 and 8.0 was explored using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy, and comparison with a conventional glassy carbon electrode was made. Dipyrone was best determined by differential pulse voltammetry with a low limit of detection of 1.4 microM. Application to commercial samples was demonstrated.

Electrochemical processes, which underlie the use of conductive diamond electrodes for the simultaneous detection of two or more metal ions in solution by anodic stripping voltammetry (ASV), have been investigated. The model analyte system studied contains the two metal species, Ag+(aq) and Pb2+(aq), and the experimental techniques employed include cyclic and square wave voltammetries, along with X-ray photoelectron spectroscopy and secondary electron microscopy. Although the bulk metallic forms of Ag and Pb are immiscible, several interactions in the system between the two metal species present are observed, which significantly influence the electrodeposition and electrodissolution processes which underlie ASV. The subsequent nucleation and growth of a given metal on the electrode surface is enhanced by the presence of the second metal on the surface. The encapsulation of one metal by the other, within the metal particulates that form on the electrode surface, significantly reduces the stripping yield at the potentials characteristic of the individual metals. The stripping potentials are also influenced by bonding interactions between deposited Ag and Pb, which broaden the characteristic stripping peaks in cyclic voltammetry, as well as producing underpotential deposition and stripping. Given these interactions, the extent to which ASV at diamond electrodes can be used to determine the solution concentrations of Ag+(aq) and Pb2+(aq) is considered.

Trace measurements of rhodium by adsorptive stripping voltammetry

The voltammetric behaviors of 1-(3-Fluoro-benzenesulfonyl)-5-{3-[5-(3-methoxy-phenyl)-2-methyl-2H-[1,2,4]triazol-3-yl]-phenyl}-1H-indole (5b) have been investigated in Britton- Robinson (B-R) buffer pH 7.0 using differential pulse voltammetry (DPV), anodic stripping voltammetry (ASV) and cyclic voltammetry (CV) on a glassy carbon electrode νs Ag/AgCl reference electrode. The preliminary observation for 5b was investigated using DPV technique in B-R buffer pH 7, a broad differential pulse voltammetric oxidation wave at E a = 0.65V was observed. The voltammetric oxidation process has been shown to be irreversible and the diffusion is controlled with adsorption characteristics. The developed anodic stripping voltammetric (ASV) was used to study some optimized experimental conditions such as accumulation time, accumulation potential, scan rate, frequency, pulse amplitude, other working electrodes and convection rate. A calibration curve for 5b was studied from 2×10 -6 to 3×10 -5 M (correlation coefficient = 0.994, n=8) under optimum conditions and the detection limit was 8×10 -8 M. The used anodic stripping voltammetric method shows a good reproducibility (n=8) for 5b with relative standard deviation RSD% was 0.54% and a good stability. An accuracy of the developed ASV was evaluated via the mean recovery of 97%±1.0. Some interference, usually present in pharmaceutical compounds, has been also evaluated. The analytical applications of the developed ASV technique were carried out for a direct determination of 5b in medical preparations and biological fluids.