Hongding Xu

Application of the sol-gel technique to polyoxometalates: towards a new chemically modified electrode

Abstract A novel chemically-modified electrode containing 12-molybdophosphoric acid was achieved on the surface of platinum electrode by sol-gel technique. The electrochemical behavior of the modified electrode was characterized by cyclic voltammetry in detail. The film electrode obtained was very stable and exhibited electrocatalytic response for reduction of bromate, chlorate and hydrogen peroxide. Hydrogen peroxide was determined amperometrically at the modified electrode in the concentration range of 3×10 −2 to 2×10 −5 M and a detection limit of 7×10 −6 M (signal-to-noise ratio 3).

Electrochemical determination of iodide on a vanadium oxide-polypropylene carbonate coated glassy carbon electrode.

A vanadium oxide-modified glassy carbon electrode was simply and conveniently fabricated by casting vanadium tri(isoproxide) oxide (VO(OC(3)H(7))(3)) and poly(propylene carbonate) (PPC) onto the glassy carbon electrode surface. The electrochemical properties of iodide at the VO(OC(3)H(7))(3)-PPC film-modified glassy carbon electrode were investigated by cyclic voltammetry, and an anodic peak was observed at approximately +0.71V (vs. SCE). Based on this, a sensitive and convenient electrochemical method was proposed for the determination of iodide. Flow injection amperometry (FIA) exhibited a good linear relationship with the concentration of iodide in the range of 5x10(-7)molL(-1) and 1x10(-3)molL(-1), and the detection limit was 1x10(-7)molL(-1). Quantitative recovery of iodide in synthetic samples has been obtained and the interferences from different cations and anions have been studied. The method has been successfully applied to the determination of iodide in dry edible seaweed. The concentrations of iodide measured by this method are in good agreement with those obtained by spectrophotometric method.

Voltammetric determination of 5-hydroxydole-3-acetic acid in human gastric juice

A method for the determination of the major serotonin metabolite--5-hydroxyindole-3-acetic acid (5-HIAA) in human gastric juice by cyclic voltammetry was described. The measurement conditions were investigated. The potential window was chosen from +0.1 to +0.9 V, the supporting electrolyte was 0.025 M PBS solution (pH 2.0). The method allowed determination in the concentration range from 2.0 x 10(-7) to 2.0 x 10(-5) M and a detection limit of 80 nM. When samples of gastric juice were analyzed with the method, we obtained the mean content of 5-HIAA in the gastric juice. Meanwhile, interference from other ions and substances were examined. The experimental results indicate that the method for the determination of gastric juice samples is successful.

The Electrochemical Behavior of UO22+ Incorporated in Thin Sol-Gel Film on the Glassy Carbon Electrode and the Determination of Cupferron

A novel kind of electrode for determination of ammonium nitrophenylhydroxyamine (Cupferron) was developed via an easy and effective immobilization method using an acid-catalyzed sol-gel technique. The electrode comprised uranyl nitrate (UO2(NO3)2) immobilized by the thin silica sol-gel film on a glassy carbon electrode (GCE). The UO2(NO3)2 retained its good preconcentration characteristic when being doped by the sol-gel film. Cupferron was determined by the direct reduction at the silica sol-gel immobilized UO2(NO3)2 electrode. Moreover its electrochemical behavior was also investigated. The determination conditions for Cupferron were optimized. The UO22+ film electrode still retained high stability after three months. The experimental results show that this method for Cupferron determination possessed good reproducibility and applicability.