ELECTROCHEMICAL STUDY OF ISOPOLYOXOMETALLATES AND HETEROPOLYOXOMETALLATES FILM MODIFIED MICROELECTRODES .1. PRETREATMENT AND MODIFICATION OF THE MO80-26(4-) MODIFIED CARBON-FIBER MICROELECTRODE

In this paper the preparation of isopoly- and heteropolyoxometallates (IPA and HPA) thin film modified carbon fiber (CF) microelectrodes and the factor that influences the modification of IPA and HPA films are described. IPA and HPA film modified CF microelectrodes can all be prepared by cyclic potential scan and simple dip coating. The modified electrodes prepared are very stable and reversible in acidic solution with monolayer characteristics. The electrochemical pretreatment of CF microelectrodes plays an important role in the modification of IPA and HPA film. The absorption of IPA and HPA film on electrode surfaces has been discussed on the basis of surface conditions of the CF microelectrode and the structure of IPA and HPA.

ELECTROLYTE EFFECTS ON THE ELECTROCHEMICAL POLYMERIZATION OF N-BENZYLANILINE

The electrochemical behaviour of N-benzylaniline polymerization is determined by the nature of the electrolyte. The voltammograms for a poly-N-benzylaniline modified Pt electrode prepared in 1 M HCl (abbreviated to PBAn(HCl)), and 1 M H2SO4 (PBAn(H2SO4)) tested in 1 M hydrochloric, sulfuric, and perchloric acid were almost superimposable. The polymer film electrode prepared in 1 M HClO4 (abbreviated to PBAn(HClO4)) is electroinactive, and exhibits only charging behaviour in 1 M HClO4 solution and can be activated in hydrochloric or other acid electrolytes with a smaller anion. These interesting phenomena are explained in terms of the anions catalyzing the loss of benzyl groups.

ELECTROCHEMICAL STUDY OF CHOLINE DERIVATIVES TRANSFER ACROSS THE LIQUID LIQUID INTERFACE

Transfer behaviors across the water/nitrobenzene interface were studied for five choline derivatives by chronopotentiometry with linear current scanning, cyclic voltammetry and differential pulse voltammetry. The irreversible hydrolysis reactions coupled to the phase transfer of ions across the water/nitrobenzene interface were observed. The Gibbs energies of the transfer of choline derivatives show the effects of an additive constitution on hydrophobic property of the medicine.

COBALT PORPHYRIN NAFION FILM ON CARBON MICROARRAY ELECTRODE TO MONITOR OXYGEN FOR ENZYME ANALYSIS OF GLUCOSE

A microcarbon array electrode was modified by the placement of a Nafion film containing cobalt tetramethylpyridyl phorphyrin on its surface. This electrode was applied to the analysis of solution glucose when it was further modified by the immobilization of glucose oxidase on the outermost surface of the Nafion by the cross-linking of serum albumin with glutaraldehyde. The concomitant decrease in the concentration of oxygen, as it was consumed in the enzymatic reaction of glucose with glucose oxidase, was determined by either cyclic voltammetry or a double potential step method at the porphyrin-Nafion catalytic electrode. Glucose could be determined in the range of 0.01-4 mM rapidly, without interference from substances such as ascorbate or other saccharides.

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.

AN ELECTROCHEMICAL MICROSENSOR FOR CHLORIDE

The potential-response of a microdisk electrode made with a chloride-doped polypyrrole (PPY) film on a carbon fibre (CF) has been examined. The effect of the polymerization conditions on the response characteristics is discussed. The optimum conditions for preparing the electrode are: cycling potential from +0.8 to +1.0 V in 0.1-0.2M pyrrole (Py) containing 0.1M LiCl, electropolymerization time 15-20 min. The electrode gives a Nernstian response of 56-58 mV/pCl and a detection limit of 3.6 x 10(-5)M chloride. It has the advantages of low resistance, short conditioning time and fast response. It has been used satisfactorily for detection of chloride in serum.

ELECTROCHEMICAL INVESTIGATION OF LIQUID/LIQUID SYSTEMS USING VARIOUS ORGANIC SOLVENTS

The potential windows of the system water/pure solvent (W/P) and water/solvent mixtures(W/S) have been investigated by cyclic voltammetry with solvents whose dielectric constants lie between 5.87 and 34.82. In the presence of LiCI in the aqueous phase and tetrabutytammoniumtetraphenylborate(TBATPB) in the organic phase, the systems water/allyl iso-thiocyanate (W/AIT) and water/nitrobensene (W/NB) show a same wide epotential window. thermodynamic parameters of ion transfer W/AIT interface were determined. In systems of W/P and V/S the influence solvent effect on the standard gibbs energies of transfer of was discussed.

ELECTROCHEMICAL-BEHAVIOR OF HETEROPOLY PHOSPHOMOLYBDOVANADATE ANIONS AT THE LIQUID LIQUID INTERFACE

Electrochemical transfer behavier of the V~vMo_(11)-V_5~vMo_7 heteropolyanions at the water/nitrobenzene interface has been investigated by using cyclic voltammetry. The effect of the solution acidity on the transfer behavior and the stable pH range of heteropolyanions were observed. Mixed melybdovanadate anions are more stable than 12-molybdophosphoric acid, however, the stability of the former decreases with increasing number of vanadium atoms. The main transfer species within the "potential window" has t...

INVESTIGATION OF ELECTROCHEMICAL-BEHAVIOR OF ARS ON GC ELECTRODE BY SPECTROELECTROCHEMISTRY WITH LOPTLC

The electrochemical behavior of Alizarin Red S(ARS) on GC electrode has been studied in acidic condition by spectroelectrochemistry with LOPTLC. It was found that there are three electrochemical reactions and followed by a chemical reaction of ARS in the potential range of 1.00——0.60V. The mechanism of electrode reactions has been studied and suggested based on the informations obtained from electrochemical and insitu spectroelectrochemical experiments.