The oxidation of ascorbate at poly(aniline)–poly(vinylsulfonate) composite coated electrodes

Abstract

Poly(aniline)–poly(vinylsulfonate) composite coated glassy carbon electrodes are shown to be good electrocatalytic surfaces for the oxidation of ascorbate at 0.1 V s. SCE and pH 7. The observed currents are both reproducible and repeatable thus enabling a detailed study of the kinetics of the reaction. For ascorbate concentrations up to 5 mmol dm⁻³ the current is mass transport limited at the rotating disc electrode. At higher concentrations (above 40 mmol dm⁻³) the current becomes independent of ascorbate concentration. The current is independent of polymer film thickness at all ascorbate concentrations. The currents for ascorbate oxidation as a function of concentration, electrode rotation speed, film thickness and electrode potential are analysed in terms of a model in which the ascorbate forms a reactive complex at the surface of the polymer film and then undergoes oxidation within this complex. This kinetic scheme is similar to that already demonstrated for the oxidation of NADH at polymer coated electrodes of this type. Finally it is shown that NAD⁺ reversibly inhibits the oxidation of ascorbate suggesting that ascorbate oxidation occurs at the same sites on the polymer surface as NADH oxidation.