Oxidation at a sol-gel composite electrode doped with a dirhodium-substituted polyoxometalate for amperometric detection of peptides separated by HPLC.

Oxidation of a variety of compounds, including methionine (Met), using a complex formed between dirhodium(II) acetate and the lacunary form of phosphotungstic acid as the catalyst is effective over a wide range of conditions, including pH 2-10. Thus, amperometric detection at a composite in which this complex is immobilized in a sol-gel material does not place restrictions on selection of conditions for separations by reverse-phase HPLC. A demonstration of this point is shown by a study of Met, Met-Phe, Phe-Met, Met-Met, and Gly-Met-Gly (Phe, phenylalanine; Gly, glycine). Using a 0.05 M phosphate buffer at pH 6.7, a C18 column, and a flow rate of 1 ml min(-1), capacity factors for Met, Gly-Met-Gly, Met-Met, and Phe-Met were 1.4, 2.1, 5.6, and 34, respectively. Phe-Met and Met-Phe co-eluted.