STANDARDIZATION OF CATION-EXCHANGE CLEANUP PRIOR TO GAS-CHROMATOGRAPHY OF AMINO-ACIDS

The optimum conditions for the cation-exchange clean-up of amino acids, present in protein hydrolysates, prior to their gas chromatographic determination were investigated. The results of exchaustive study monitoring the amounts of amino acids as N,O(S)-trifluoroacetyl isobutyl esters, revealed that the recovery of amino acids from the column was affected appreciably by either the particle size or the divinylbenzene content of the resins. Quantitative recovery and reproducible determination of amino acids require (i) a 50-fold excess of resin (calculated as equivalent capacity relative to the amino acids present) and (ii) sufficient amounts of eluates: the volumes both of distilled water and of 7 M ammonia solution must be about six times the volume of the wet resin applied. Under optimum conditions the recoveries of alanine, glycine, threonine, serine, valine, leucine (isoleucine), proline, hydroxyproline, methionine, aspartic acid, phenylalanine, ornithine, glutamic acid, tyrosine, lysine, arginine and cystine, were quantitative, both without and after hydrolysis, and that of tryptophan was ca. 85%.