LCEC OF UNDERIVATIZED POLYPEPTIDES AND PROTEINS AT COPPER ELECTRODES

Constant potential amperometric detection of underivatized polypeptides and proteins can be carried out at metallic copper electrodes. When coupled with liquid chromatography, this approach provides a sensitive and selective method of analysis for these compounds. Two different detection mechanisms can be employed: a neutral pH, low potential oxidation process attributed to enhanced dissolution of the electrode by peptide species capable of forming soluble Cu(II) complexes and a high pH, high potential electrocatalytic oxidation of the analytes. Of the two approaches, the latter process was found to be more attractive for LCEC applications as it was useful for a wider range of peptides and proteins and gave substantially larger currents and lower detection limits. The compounds exhibiting useful electrocatalytic response at the copper electrode ranged from oligopeptides such as enkephalins and bradykinin to very large proteins such as glucose oxidase (F.W. 160,000) and catalase (F.W. 240,000). The response was not dependent on the presence of tyrosine, tryptophan, or cysteine amino acid units and was shown to be compatible with both ion-exchange and reverse-phase separation schemes.