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

Thin films of the redox polymer, [Ru(bpy)(2)PVP10] (ClO4)(2), deposited on electrode surfaces are effective mediators for the oxidation of oxalate, bp y is 2,2'-bipyridyl and PVP is poly-4-vinylpyridine. The effects of systema tically Varying the electrode rotation rate, the film thickness and the ele ctrode potential, on the modified electrode rate constant reveal that the c atalytic current is limited by the kinetics of the cross-reaction and that the reaction takes place throughout the layer (Lk mechanism). The rate cons tant for the cross-reaction of the Ru3+ centres with oxalate is 3.1 x 10(2) M-1 s(-1). Diffusion of the analyte through the layer is relatively unimpe ded and a value of 3.3 x 10(-6) cm(2) s(-1) is observed for the diffusion c oefficient. In sulphuric acid electrolyte, charge transport through the fil m is a diffusion Like process and the charge transport diffusion coefficien t, D-CT, as measured by both cyclic voltammetry and chronoamperometry is 2 x 10(-11) cm(2) s(-1). This charge transport rate is independent of the con centration of sulphuric acid as supporting electrolyte indicating an open p orous layer structure in this medium. The application of the layers for amp erometric detection of oxalate is demonstrated using a flow injection analy sis system. A linear response range extending from 2 x 10(-5) to 6 x 10(-3) M was obtained with a detection limit of 0.35 ppm. The precision of the re sponse of the system is evaluated (1.53% RDS for 10 repeated injections), a s is the response time (9.8 s for 98% of the maximum response). The possibi lity of using the layers for simultaneous detection of current and electrog enerated chemiluminescence is considered. (C) 1999 Elsevier Science B.V. Al l rights reserved.