ELECTROCATALYSIS AT A MICRODISK ELECTRODE MODIFIED WITH A REDOX SPECIES

The current equation of the electrocatalytic reaction at a microdisk electrode modified with redox species has been described and verified experimentally. There exists a linear relationship between plateau limiting current and the radius of the microdisk electrode for a catalytic process. The influence of the dimensions of the microdisk electrode on catalytic efficiency is discussed. The polyvinylferrocene (PVFc)-modified microdisk electrode prepared by the coating method was taken as a typical example, on which the electrocatalytic oxidation of ascorbic acid could be studied. The catalytic reaction rate constants were determined as an average value of 1.5 X 10(-7) cm3/mol s by this method, and are consistent with those obtained at a conventional electrode.

ANODIC-OXIDATION OF HYDRAZINE ON GLASSY-CARBON MODIFIED BY MACROCYCLIC TRANSITION-METAL COMPLEXES .1. COBALT PROTOPORPHYRIN DIMETHYL ESTER MODIFIED ELECTRODE

The electrocatalytic oxidation of hydrazine (N2H4) on a glassy carbon electrode (GC) modified by monolayer and polymer films of cobalt protoporphyrin dimethyl ester (CoPP) has been studied. Both the monolayer and polymer films of CoPP are very active to the anodic oxidation of N2H4. The activity of CoPP for the anodic oxidation of N2H4 is dependent on the pH of the solution, and the thickness of polymerized CoPP film. The oxidation kinetics were examined by methods of cyclic voltammetry, rotating disc electrodes and steady-state polarization measurement.

DIRECT ELECTRON-TRANSFER REACTION OF HEMEPROTEINS PROMOTED BY METHYLENE-BLUE MODIFIED ELECTRODE

The heterogeneous electron transfer reaction of hemeproteins including hemoglobin, myoglobin and cytochrome C at Pt mesh electrode adsorbed methylene blue has been investigated. Thin-layer spectroelectrochemical technique was used for observing the electron transfer processes of three kinds of proteins, and the corresponding electrode rate constants were measured.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CARBOXYLIC-ACIDS AND PHENOLIC-ACIDS WITH A COPPER-BASED CHEMICALLY-MODIFIED ELECTRODE

A copper-based chemically-modified electrode has been constructed and characterized by various experimental parameters in flow-through amperometric detection of carboxylic acids and phenolic acids. Novel hydrodynamic voltamperograms were first obtained in flow-through amperometric detection with the Cu-based CME and subsequently negative and positive peaks were observed in a single chromatogram. This unique and flexible potential dependence could be of great benefit in chromatographic speciation and quantification. These observations suggest that the detector response was governed by the complexation reaction of copper ions with the solutes.

A GLASSY-CARBON ELECTRODE MODIFIED BY DISPERSED ALPHA-ALUMINA AS AN ENHANCED ELECTROCHEMICAL DETECTOR IN LIQUID-CHROMATOGRAPHY FOR CYSTEINE AND GLUTATHIONE

The dispersion of alumina particles on a glassy-carbon surface serving as a modified electrode significantly enhances the amperometric detection of cysteine and glutathione following liquid chromatography. With an applied potential of 0.8 V vs. SCE, the detection limits were 1.2 ng for cysteine and 8 ng for glutathione and the electrode response was linear up to 600 ng for cysteine and 1.8-mu-g for glutathione. The modified electrode displayed high sensitivity and stability and was easy and inexpensive to prepare.

FLOW-INJECTION ANALYSIS OF MYOGLOBIN AND HEMOGLOBIN AT TOLUIDINE BLUE CHEMICALLY MODIFIED ELECTRODE

Electrodeposition of the phenothiazine mediator titrant toluidine blue onto a glassy carbon substrate at an appropriate potential was used to construct a toluidine blue chemically modified electrode (CME) exhibiting electrocatalytic reduction for myoglobin and hemoglobin. The CME catalyzed the hemoprotein electroreduction at the reduction potential of the mediator molecule. When the CME as used as a detector for flow injection analysis at a constant applied potential of -0.30 V vs. a saturated calomel electrode, it gave detection limits of 20 and 50 ng (1.2 and 0.78 pmol) injected myoglobin and hemoglobin, respectively, with a dynamic linear concentration range over 2 orders of magnitude. After a brief equilibration period, the CME retained nearly 90% of its initial myoglobin response over 8 hours of continuous exposure to the flow-through system.

THE USE OF CHEMICALLY MODIFIED ELECTRODES FOR LIQUID-CHROMATOGRAPHY AND FLOW-INJECTION ANALYSIS

The use of chemically modified electrodes (CMEs) for liquid chromatography and flow-injection analysis is reviewed. Electrochemical detection with CMEs based on electrocatalysis, permselectivity, ion flow in redox films, and ion transfer across the water-solidified nitrobenzene interface is discussed in terms of improving the stability, selectivity, and scope of electrochemical detectors, and the detection of electroinactive substances. More than 90 references are included.

ELECTROCATALYSIS OF POLYPYRROLE-METHYLENE BLUE FILM MODIFIED ELECTRODE FOR DIRECT REDOX REACTION OF CYTOCHROME-C

The electron transfer process of hemeproteins on the electrode surface is considered a promising subject in the area of bioelectrochemistry. Electrochemists believe that electron transfer between electroactive proteins and electrode surface might be expected to simulate the electron transfer between proteins. This research provides information about the electron transfer mechanism in biological system. Cytochrome c is a typical electron transferring protein,

THE ELECTROCATALYTIC OXIDATION OF ASCORBIC-ACID ON PRUSSIAN BLUE FILM MODIFIED ELECTRODES

The kinetics of prussian blue (PB) film itself during the redox process and of the catalytic oxidation of ascorbic acid (AH_2) on it have been studied in detail. The charge transfer diffusion coefficient D_(ct) in PB film is determined as 2.62×10~(-10)cm~2·s~(-1), using potential-step chronoamperometry, chronocoulometry and constant-current chronopotentialmetry, respectively. The rate constant of the cross-exchange reaction between AH_2 in solution and the active centers in PB film is measured in rotating d...

THE REVERSIBLE ELECTRON-TRANSFER REACTION OF MYOGLOBIN AT BRILLIANT CRESYL BLUE MODIFIED PLATINUM GAUZE ELECTRODE

The electrochemical behavior of myoglobin at a Brilliant Cresyl Blue (BCB) modified platinum gauze electrode and spiral pt wire in the BCB solution in optically transparent thin layer cell base been investigated by using cyclic potential-absorbance method and double potential step chronoabsorptometry. The results reveal a reversible electron transfer resection of myoglobin. Exhaustive reductive and oxidative electrolyses are achieved at the modified platinum surface in 20 and 100s respectively. The formal h...