Selective silylation usingtert-butyldimethylsilyl reagents: Their use in the quantification of fatty acids

Abstract

The modification of alcoholic and phenolic compounds as their tert-butyldimethylsilyl ether derivatives has found wide use in the separation of complex mixtures by gas chromatography and in their quantification by gas chromatography mass spectrometry with selected ion monitoring. In comparison, the formation and use of the tert-butyldimethylsilyl ester derivatives has received little attention. This paper examines some of the factors involved in the esterification of fatty acids using a number of tert-butyldimethylsilyl reagents, delineating optimum conditions for derivative formation. In addition, using hydroxy fatty acids, differences in the selectivity of silylation between these tert-butyldimethylsilyl reagents and their trimethylsilyl analogues are demonstrated, which are manifested in the discrimination between silyl ester and silyl ether formation. The application and limitation of these techniques is discussed with reference to the quantification, by gas chromatography mass spectrometry selected ion monitoring of unsaturated fatty acids and hydroxy fatty acids as their tert-butyldimethylsilyl derivatives. The measurement of arachidonic acid obtained from human skin, where sample size is often limited, is illustrated using a stable isotope dilution assay. These results are compared to those obtained using the methyl ester.