Deuteration as an aid to the high-temperature gas chromatography—mass spectrometry of steryl fatty acyl esters

Abstract

A method is presented for reducing degradative losses of steryl fatty acyl esters bearing polyunsaturated fatty acyl moieties during high-temperature gas chromatography (GC) and combined high-temperature GC—mass spectrometry (MS). The method employs selective deuteration of the double bonds in the fatty acyl moiety using a homogeneous catalyst (Wilkinson's catalyst). The Δ 5 double bond, which occurs in the most commonly occurring plant and animal sterols, is not deuterated under the conditions described. In addition to improving GC behaviour, the method has the advantage of preserving structure information by labelling each double bond present in the original unsaturated fatty acyl moiety. The carbon number and degree of unsaturation of the labelled fatty acyl moiety are readily revealed by combined GC—MS employing negative-ion ammonia chemical ionisation. Two applications of the method are demonstrated in the analysis of steryl fatty acyl esters isolated from a rape seed oil and ovary tissue of the marine prawn Penaeus monodon.