CONSTANT POTENTIAL AMPEROMETRIC DETECTION OF UNDERIVATIZED AMINO-ACIDS AND PEPTIDES AT A COPPER ELECTRODE

Direct detection of underivatized amino acids and peptides can be carried out via oxidation at copper electrodes. Two different oxidation processes are possible, depending on the applied potential and the prevailing solution conditions. The first, which occurs optimally in neutral or slightly basic solution at approximately 0.0 V vs Ag/AgCl, is related to complexation reaction between the amino acid analyte and Cu(II) from the passivated electrode surface. The second mechanism, which occurs optimally under strong alkaline conditions in the +0.4-0.8-V range, appears to involve the electrocatalytic oxidation of the amino acid species. Of the two, the latter process was the more attractive for constant potential amperometric detection in flow injection and liquid chromatography applications as it allowed detection down to the 1-10 pmol levels for most amino acids and simple peptides. Furthermore, the Cu electrode response was comparatively long-lived, with single-electrode surfaces typically showing analytically useful activity for periods as long as 2 weeks.