FLOW-INJECTION ANALYSIS OF GLUCOSE AT AN AMPEROMETRIC GLUCOSE SENSOR-BASED ON ELECTROCHEMICAL CODEPOSITION OF PALLADIUM AND GLUCOSE-OXIDASE ON A GLASSY-CARBON ELECTRODE

A glassy carbon electrode (GCE) modified with palladium provides excellent electrocatalytic oxidation of hydrogen peroxide. When the electrolyte contains palladium chloride and glucose oxidase, the GCE can be modified by electrochemical codeposition at a given potential. The resulting modified surface was coated with a thin film of Nation to form a glucose sensor. Such a glucose sensor was successfully used in the flow-injection analysis of glucose with high stability and anti-poisoning ability. It gave a detection limit of 1 X 10(-7) M injected glucose, with a linear concentration range of 0.001-8 mM. There is no obvious interference from substances such as ascorbate and saccharides.

ELECTROCATALYSIS AND DETERMINATION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A MIXED-VALENT COBALT OXIDE CYANOCOBALTATE FILM ELECTRODE

A glassy carbon electrode coated with an electrodeposited film of mixed-valent cobalt oxide/cyanocobaltate (Co-O/CN-Co) enabled hydrazine compounds to be catalytically oxidized at the greatly reduced overpotential and in a wide operational pH range (pH 2.0-7.0). Electrocatalytic activity at the Co-O/CN-Co modified electrode was evaluated with respect to solution pH, film thickness, supporting electrolyte ions, potential scan rate, operating potential, concentration dependence and other variables. The Co-O/CN-Co film electrode was completely compatible with a conventional reversed-phase liquid chromatographic (RP-LC) system. Practical RP-LC amperometric detection (RP-LCEC) of hydrazines was performed. A dynamic linear response range over three orders of magnitude and a detection limit at the pmol level were readily obtained. The Co-O/CN-CO film electrode exhibited excellent electrocatalytic stability in the flowing streams.

ELECTROCHEMICAL CATALYSIS AT AN ULTRAMICROELECTRODE MODIFIED WITH REDOX SPECIES

General equations of the electrocatalytic reaction at an ultramicroelectrode modified with redox species have been described according to the Andrieux Saveant model. The electrocatalytic kinetic process has been discussed for the whole set of cases, ie (R), (R + S), (SR) (SR + E), (E), (R + E), (ER), (S), (ER + S) and (S + E) limiting situations. The effect of gamma on the catalytic steady state current shows that the higher the value of gamma, the lower the catalytic current. The kinetic process shifts rapidly from R to E with increasing values of gamma. It is favorable for catalysis only when gamma is very low. Therefore, the redox species modified ultramicroelectrode with thin film is utilized for electrocatalysis, and the larger the radius of ultramicroelectrode, the higher the catalytic efficiency.

MEASUREMENT OF CATALYTIC ACTIVITY VARIATION FOR H2O2 OXIDATION AT A COBALT PORPHYRIN COATED ELECTRODE

A rapid rotation-scan method was used for the electrocatalytic oxidation of H2O2 at a cobalt protoporphyrin modified pyrolytic graphite electrode (CoPP/PG). The rate constant of H2O2 oxidation at the CoPP/PG electrode at different potentials and in different pH solutions was measured. The variation of catalytic activity with reaction charges (Q) passed through the electrode was analyzed. This provided a convenient electrochemical method to study the passivation and poisoning of catalytic sites with time.

STUDY ON ELECTRODE PROCESS OF MYOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode was firstly reported in this paper. A quasi-reversible electrode processes of myoglobin with the formal heterogeneous electron transfer rate constant (k(sh)) of 1.73 x 10(-4) cm.s-1 at the polymerized azure A modified electrode have been achieved using in-situ UV-visible spectroelectrochemistry. The adsorption of myoglobin on the polymerized azure A film electrode surface was confirmed by XPS. With simultaneously studying of cyclic voltammetry and in-situ cyclic voltabsorptometry, the attribution of the voltammetry responses of myoglobin at the film electrode has been studied. The mechanism for the heterogeneous electron transfer of myoglobin at the polymerized azure A film modified electrode has been proposed as well.

ELECTROCHEMICAL STUDY OF ISOPOLY-OXOMETALLATE AND HETEROPOLY-OXOMETALLATE FILM MODIFIED MICROELECTRODES .2. ELECTROCHEMICAL-BEHAVIOR OF ISOPOLYMOLYBDIC ACID MONOLAYER MODIFIED CARBON-FIBER MICROELECTRODES

In this paper the electrochemical properties of isopolymolybdic anion thin film modified carbon fibre (CF) microelectrode prepared by simple dip coating have been described. The modified electrode shows three couples of surface redox waves between + 0.70 and - 0.1 V vs. sce in 2 M H2SO4 solution with good stability and reversibility. The pH of solution has a marked effect on the electrochemical behaviour and stability of the film, the stronger the acidity of electrolyte solution is, the better the stability and reversibility of isopolymolybdic anion film CF microelectrode will be. The scanning potential range strongly influences on the electrochemical behaviour of the film. The isopolymolybdic anion film prepared by the dip coating resulting a monolayer with estimated surface concentration (F) 2.8 x 10(-11) mol cm-2. From the half-peak widths and peak areas of the surface redox waves of the film electrode, the first three surface waves are corresponding to two-electron processes. The electron energy spectra show the products by six electrons reduction are a mixture of Mo(VI) and Mo(V) species. The electrochemical reaction of the isopolymolybdic anion monolayer can be expressed as Mo8O264- + mH+ + 2ne half arrow right over half arrow left [HmMo8-2n(VI)Mo2n(V)O26](4,2n-m)-n = 1, 2, 3; m = 2, 5, 7.

ELECTROCHEMICAL STABILITY AND ELECTROCATALYSIS BEHAVIORS OF POLY(3-METHYLTHIOPHENE) THIN-FILM MODIFIED ELECTRODES

The Electrochemical stability of poly(3-methylthiophene) (PMT) thin film modified glassy carbon electrodes was investigated experimentally with successive cyclic voltammetry(CV) The effects of electrolyte solutions on the stability were studied. In the presence of small hydrated anions (less-than-or-equal-to 3.5nm) in the solution, the electroactivity of PMT films decreased with the characteristics of second order kinetics. In a solution with large hydrated anions (greater-than-or-equal-to 4 nm), PMT films have good stability. PMT/GO electrode can electrocatalyse the oxidation of Br- and Cl- anions, and loses its electroactivity rapidly. X-ray photoelectron spectra (XPS) have demonstrated that chlorine has bonded covalently onto the PMT structure after OV cycles in NaCl solutions.

ELECTROCATALYTIC OXIDATION AND FLOW DETECTION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A VITAMIN-B-12 ADSORBED GLASSY-CARBON ELECTRODE

A vitamin B-12 chemically modified electrode (CME) was constructed by adsorption of vitamin B-12 onto a glassy carbon surface. The electrode catalyzes the electrooxidation of hydrazine compounds over a wide pH range. The electrocatalytic behavior of hydrazines is elucidated with respect to the CME preparation conditions, solution pH, operating potential, mobile phase flow rate, and other variables. When applied to liquid chromatographic detection of the analytes, the vitamin B-12 CME yielded a linear response range over 2 orders of magnitude, and detection limits at the picomole level. The vitamin B-12 CME offers acceptable catalytic stability in both batch and flow systems.

A STUDY ABOUT PH CHEMICALLY MODIFIED ELECTRODES BASED ON AMINO-DERIVATIVES OF NAPHTHALENE

The electrochemical polymerization of amino-derivatives of naphthalene has been studied on the platinum wire electrodes. The effects of acidity of the modifying media and the potential scan rate on the cyclic voltammograms are verified. As potentiometric pH sensors, the electrodes prepared from 1-naphthylamine and 2,3-diaminonaphthalene showed performance characteristics superior to some other electrodes tested. The electrode modified with 1-naphthylamine in the optimum medium showed a nearly Nernstian response of 4.20-13.70 pH and a slope of -54.8 mV/pH, while the linear range of the electrode prepared by 2,3-diaminonaphthalene was 4.00-13.60 pH, with a slope of -52.4 mV/pH.

ELECTROCATALYTIC OXIDATION OF ASCORBIC ACID AT POLYANILINE FILM MODIFIED GLASSY CARBON ELECTRODES

A conducting polyaniline (PAn) film modified glassy carbon (GC) electrode was prepared by electrochemical polymerization. The electrochemical behavior of ascorbic acid (AH(2)) in aqueous solution at this PAn modified electrode was studied in detail. The experimental results show that PAn film modified electrode has good electrocatalytic activity on the oxidation of ascorbic acid in aqueous solution over a wide range of pH value, among which pH 4 is the optimum condition. The oxidation process of ascorbic acid at PAn film electrode can be regarded as an EC catalytic mechanism. The kinetic process of the catalytic reaction was investigated by rotating disk electrode (RDE) coated with PAn films. The rate constant of the catalytic reaction was evaluated. The catalytic peak currents are proportional to the concentrations tions of ascorbic acid in the range of 5 x 10(-2)-1 x 10(-6) mol . L-1. The PAn film elec trodes give very stable responce for the oxidation of ascorbic acid. The present investigation shows the posibility of using PAn film modified electrode for the determination of ascorbic acid.

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.

THE IMPEDANCE STUDY OF MODIFIED PEO POLYMER ELECTROLYTE

The ultra-thin modified PEO (polyethylene oxide)-LiClO4 polymer electrolyte film (50-mu-m) was obtained by solution-casting technique. Impedance spectra were taken on the cells consisting of above PEO film electrolyte and ion-blocking or nonblocking electrodes. The ambient conductivity as high as 1.33 X 10(-4)S cm-1 could be achieved for PEO electrolyte modified by the crosslinking. It was shown that the resistance at the interface between solid polymer electrolyte and lithium electrode is growing with increasing the storage time. At high temperature, as 96-degrees-C, the ionic transport is clearly controlled by diffusion.

ELECTRODEPOSITION OF PLATINUM PARTICLES ON GLASSY-CARBON MODIFIED WITH COBALT PORPHYRIN AND NAFION FILM AND THEIR ELECTROCATALYTIC REDUCTION OF DIOXYGEN

In this paper, five types of chemically modified electrode (CMEs) prepared with the deposition of platinum particles on various surfaces of glassy carbon (GC) modified with cobalt porphyrin and Nafion(R) solution are characterized using the electron scanning microscope (SEM). Their activities in the four-electron reduction of dioxygen to water on the basis of their electrochemical data from cyclic voltammetric and rotating ring-disk electrode (RRDE) experiments are examined and compared. Platinum particles dispersed on the GC surface adsorbed with the cobalt porphyrin exhibit the highest activity for the electrocatalytic reduction of dioxygen. However it is interesting that the cobalt ion is lost from the center of the porphyrin ring during the preparation of the cobalt porphyrin + Nafion mixture solution, while the porphyrin ring still remains in the Nafion film, as shown by EDX analysis. The incorporation of the porphyrin may change the structure of the Nafion film into a looser form, since the platinum particles dispersed in the film are more readily exposed, resulting in more favourable mass transfer and higher activity for the electrocatalytic reduction of dioxygen.

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.