A technique described later which gave a complete baseline separation of Dimethylaminoazobenzene sulfonyl (DABS)-amino acids employed a LiChrosorb RP-18 column operated at 50°C in conjunction with a complex gradient based on dimethylformamide, acetonitrile, and phosphate or acetate buffer. G. Winkler et al. attempted to optimize the chromatographic conditions so as to obtain complete separation of DABS-amino acids at room temperature. The DABS-C1 method requires no postcolumn derivatization apparatus and the same instrument can be used for peptide isolation. Moreover, DABS-amino acids are stable compounds and unusual amino acid derivatives can be recovered for further study. The most critical parameter was pH. Optimum pH conditions had to be ascertained for each special column, and also for each new column from the same manufacturer. J. Y. Chang et al. demonstrated in 1981 that amino acids labeled with dimethylaminoazoben-zenesulfonyl chloride could be separated using a Zorbax octadecylsilane column and detected in the visible region.