SELECTIVE DETECTION IN RB 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 similar to + 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.