The oxidation of ascorbate at poly(aniline)-poly(vinylsulfonate) compositecoated electrodes

Poly(aniline)-poly(vinylsulfonate) composite coated glassy carbon electrode s are shown to be good electrocatalytic surfaces for the oxidation of ascor bate at 0.1 V vs. SCE and pH 7. The observed currents are both reproducible and repeatable thus enabling a detailed study of the kinetics of the react ion. For ascorbate concentrations up to 5 mmol dm(-3) the current is mass t ransport limited at the rotating disc electrode. At higher concentrations ( above 40 mmol dm(-3)) the current becomes independent of ascorbate concentr ation. The current is independent of polymer film thickness at all ascorbat e concentrations. The currents for ascorbate oxidation as a function of con centration, electrode rotation speed, film thickness and electrode potentia l 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 wit hin this complex. This kinetic scheme is similar to that already demonstrat ed for the oxidation of NADH at polymer coated electrodes of this type. Fin ally it is shown that NAD(+) reversibly inhibits the oxidation of ascorbate suggesting that ascorbate oxidation occurs at the same sites on the polyme r surface as NADH oxidation.