Glucose oxidation at bismuth-modified platinum electrodes

Abstract

The oxidation of glucose has been investigated at bismuth-modified polycrystalline platinum electrodes in 0.2 M NaOH containing 1–2 μM Bi(III) species by cyclic voltammetry and photoelectron spectroscopy using monochromatized AlKα excitation (XPS). The study aims to provide a foundation for the use of Bi-modified Pt electrodes for constant-potential amperometric detection of carbohydrates after anion-exchange chromatography. Bi-modified electrodes can be operated over hours in glucose solution without loss of sensitivity, while bismuth electrodes are completely inactive for glucose oxidation and Pt electrodes experience self-poisoning. Detection can be made in the double-layer region where Bi is confined to the Pt surface as an underpotential deposited (upd) layer and in the platinum oxide region where oxidized Bi species are retained as specifically adsorbed ions. Their existence could be verified by XPS. The binding energy (BE) shift of this signal indicates that the Bi species are present in an unusual oxidation state corresponding to a formal oxidation number +2. During continuous potentiostatic operation of a Bi-modified Pt electrode in glucose solution a new component in the Bi4f spectrum develops which is assigned to Bi species partially complexed by glucose or its reaction products. This makes a complex oxidation mechanism more likely than that described by the `third body model'. Different oxidation pathways can be assumed in both potential regions. In the platinum oxide region the detection is less critically dependent on the potential than in the double layer region. Electrodes transferred several times between glucose-containing and glucose-free 0.2 M NaOH+Bi(III) did not show the formation of an inhibiting layer.