Cathodic stripping voltammetry of the peptide felypressin in trace amounts

Felypressin, a peptide containing eight amino acids including cystine, is studied by cathodic stripping voltammetry (c.s.v.) at a mercury drop electrode at pH 4.6 in the concentration interval 5 × 10^?9-7 × 10^?7 M. Excess of copper(II) ions is required to obtain the c.s.v. activity. The stripping peak potential is ?0.55 to ?0.70 V vs. SCE depending on the excess of copper(II). The accumulated product is adsorbed both in its oxidized and reduced state. Interference from c.s.v.-active substances which desorb in the reduced state can be eliminated by applying a repetitive cyclic scan and evaluating the second or third scan. Lypressin and somatostatin, two other cystine-containing peptides, are also c.s.v.-active.