Selective detection in RP-HPLC of Tyr-, Trp-, and sulfur-containing peptides by pulsed amperometry at platinum

A technique for electrochemical detection of Trp-, Tyr-, and sulfur-containing peptides, using a two-step potential waveform at a platinum wall-jet electrode, has been developed. The detection is fully compatible with reversed-phase HPLC employing gradients of acetonitrile in water/trifluoroacetic acid. At approximately +1.2 V (first potential) versus Ag/AgCl, Trp-, Tyr-, and Cys-containing peptides are predominantly detected, while at +1.4 - 1.6 V, Met- and (Cys)2-containing peptides are additionally detected. The electrode surface is cleaned by the second potential (+2.0 V). the linearity is at least 2 orders of magnitude. The sensitivity is in the picomole range. By using postcolumn electrochemical conversion, the selectivity toward Met and Cys-containing peptides can be enhanced. Applications are shown for the determination of caseinomacropeptide (6.6 kDa) and a tryptic map of beta-casein.