Showing papers by "Andrew Doherty published in 1995"

Electrocatalytic oxidation of ascorbic acid at [osmium(2,2′-bipyridyl)2-(poly-4-vinylpyridine)10Cl]Cl modified electrodes; implications for the development of biosensors based on osmium-containing redox relays

Abstract: The oxidation of ascorbic acid at electrodes modified with the redox polymer [Os(bipy)2(PVP)10Cl]Cl (where bipy = 2,2′-bipyridyl and PVP = poly-4-vinylpyridine) has been studied. The reaction proceeds electrocatalytically at 0.250 V versus SCE by mediation via the OsII/OsIII redox couple immobilized in the polymer film. The reaction is negative first order with respect to proton concentration and positive first order with respect to ascorbic acid concentration. At pH3.0, limiting currents are diffusionally controlled and the kinetic regime may be classified as an Sk″ mechanism. The second order rate constant for the surface electrocatalytic reaction k″ at pH 4.5 is 7.8 ± 0.4 × 10–4dm3mol–1 cm s–1, while at pH 7.0 k″ is 9.1 ± 0.6 × 10–4 dm3 mol–1 cm s–1. At pH ⩽2.0 ascorbic acid permeates the polymer film and reacts at the mediator sites within the polymer film giving an Lk mechanism, while at potentials >0.4 V versus SCE the reaction proceeds both at the underlying electrode and with the OsIII mediator sites within the polymer film. The modified electrode has been characterized as an electrochemical sensor for ascorbic acid in flow injection systems.

The effect of the nature of the polymer backbone on the stability and the analytical response of polymer‐modified electrodes

Abstract: The synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)(2)(PS)(7.5)(DMAP)(2.5)Cl]Cl, where bipy = 2, 2'-bipyridyl, PS = polystyrene, and DMAP = poly[4-(N-methyl-N-p-vinylbenzylamino) pyridine], are described. The charge transport properties of electrodes modified with the redox material are investigated using cyclic voltammetry and chronoamperometry. The modified electrode behaves as an efficient electrocatalyst for the outer-sphere reduction of Fe-III, with the cross-exchange reaction occurring at the surface of the polymer (Sk'') at concentrations less than 1.0 x 10(-3) mol dm(-3) Fe-III, with a change over to the St(e) kinetic regime at higher substrate concentrations. Direct agreement was observed between the kinetic behavior at rotating disk electrodes and in thin-layer flow cells. Application of the modified electrodes for the determination of iron in pharmaceutical formulations and the long term stability of the electrodes are investigated. The results obtained are compared with those reported for the analogous metallopolymer [Os(bipy)(2)(PVP)(10)Cl]Cl, where PVP is poly-4-vinylpyridine.