Gas chromatography of various N(O,S) acyl alkyl esters of amino acids

Abstract

The chromatographic behaviour of various N(O,S) acyl alkyl esters of amino acids was compared. Shorter retention times were found for the propanol esters than for the corresponding butanol esters, and esters containing a secondary alcohol were eluted more quickly than those containing a primary alcohol. The trifluoroacetyl derivatives were eluted before the heptafluorobutyryl (HFB) derivatives on three different stationary phases; however, on Carbowax 20M the HFB-amino acid esters were eluted first. Differences in retention times caused by variation of the ester or the acyl group are greater with the derivatives of the small amino acids. More “compressed” chromatograms are obtained using butanol instead of propanol or the 1-instead of the 2-alcohol for esterification and heptafluorobutyric instead of trifluoroacetic anhydride for acylation. The influence of the trifluoroacetylation time on the relative molar responses does not vary significantly between the various esters tested. Methionine esters and the monoacyl derivative of the tryptophan esters are less stable to acylation when esterified with a primary alcohol.