Cathodic stripping voltammetry of selenocystine,cystine, and cysteine in dilute aqueous acid

Selenocystine, cystine, and cysteine can be determined by cathodic stripping voltammetry (c.s.v.) in 0.1 M HClO₄ or 0.1 M H₂SO₄. The amino acids are accumulated at potentials more positive than —0.35 V, —0.20 V, and —0.10 V vs. s.c.e., respectively, and the stripping peak potentials are —0.45 V, —0.38 V and —0.15 V, respectively. Limiting coverage of the mercury electrode surface is observed for cysteine and selenocystine, but not for cystine. The detection limit for selenocystine is 5 × 10^-10 M in the presence of 100-fold amounts of cystine and cysteine. The detection limits for cystine and cysteine are 1 × 10^-5 M and 1 × 10^-9 M, respectively.