DETERMINATION OF AMINO-ACIDS AND PEPTIDES BY CAPILLARY ELECTROPHORESIS AND ELECTROCHEMICAL DETECTION AT A COPPER ELECTRODE

Electrooxidation of amino acids and peptides at Cu electrodes has been shown to provide an attractive method for detection and quantitation of these compounds after separation by capillary electrophoresis (CE). As has been previously seen in analogous liquid chromatography applications, the use of Cu electrodes permitted the direct detection of amino acid species in CE at constant applied potential and without derivatization. Strongly alkaline media, typically 50-100 mM NaOH, were required for the electrode process to proceed optimally; but such media were found to be suitable for useful CE separations. The electrode used was a 127-mu m-diameter Cu disk operated in a wall-jet configuration. The detection limits so obtained varied from 1 to 10 fmol for most amino acids to a few hundred femtomoles for those containing hydrophobic sidechains. The electrodes could be used continuously for periods of at least 3-4 weeks with no apparent loss of response. Practical applications demonstrated included the determination of amino acids in human urine, of the dipeptide aspartame in diet soft drinks, and of pentapeptide products of a solid-phase synthesis procedure.