New internal standards for basic amino acid analyses

Abstract

Eight derivatives of cysteine and penicillamine with 2- and 4-vinyl-pyridine, p-nitrobenzyl bromide, and p-nitrostyrene were evaluated as potential internal standards for the short and long (physiological) basic columns in amino acid analysis by ion-exchange chromatography. S-β-(4-pyridylethyl)-dl-penicillamine (4-PEP) was found to have an advantage over the previously proposed S-β-(4-pyridylethyl)-l-cysteine (4-PEC) since the elution position of 4-PEP on the short basic column is insensitive to minor changes in pH of the eluting citrate buffer. 4-PEP was found to be stable to acid hydrolysis as used for proteins and its recovery from protein hydrolysates was unaffected by the presence of starch during hydrolysis. However, an extra 14 min is required to elute 4-PEP on the short column. Of the eight compounds studied, six appcar suitable as internal standards on the physiological (long) column. These elute in widely differing positions between histidine and arginine, thus offering a choice of internal standards for special analysis on the basic long column. © 1973.