Mediated electron transfer for electroanalysis: transport and kinetics in tin films of [Ru (bpy)2PVP10] (ClO4)2

Abstract

Thin films of the redox polymer, [Ru(bpy)2PVP10] (ClO4)2, deposited on electrode surfaces are effective mediators for the oxidation of oxalate, bpy is 2,2′-bipyridyl and PVP is poly-4-vinylpyridine. The effects of systematically varying the electrode rotation rate, the film thickness and the electrode potential, on the modified electrode rate constant reveal that the catalytic current is limited by the kinetics of the cross-reaction and that the reaction takes place throughout the layer (Lk mechanism). The rate constant for the cross-reaction of the Ru3+ centres with oxalate is 3.1×102M−1s−1. Diffusion of the analyte through the layer is relatively unimpeded and a value of 3.3×10−6cm2s−1 is observed for the diffusion coefficient. In sulphuric acid electrolyte, charge transport through the film is a diffusion like process and the charge transport diffusion coefficient, DCT, as measured by both cyclic voltammetry and chronoamperometry is 2×10−11cm2s−1. This charge transport rate is independent of the concentration of sulphuric acid as supporting electrolyte indicating an open porous layer structure in this medium. The application of the layers for amperometric detection of oxalate is demonstrated using a flow injection analysis system. A linear response range extending from 2×10−5 to 6×10−3M was obtained with a detection limit of 0.35ppm. The precision of the response of the system is evaluated (1.53% RDS for 10 repeated injections), as is the response time (9.8s for 98% of the maximum response). The possibility of using the layers for simultaneous detection of current and electrogenerated chemiluminescence is considered.