Analysis of sterol esters by capillary gas chromatography‐electron impact and chemical lonization‐mass spectrometry

Abstract

Abstract Synthetic mixtures of C 40 to C 47 sterol esters in groups of 7 esters were effectively separated and analyzed by capillary gas chromatography‐mass spectrometry. Ammonia chemical ionization of all 20 sterol esters analyzed at a source block temperature of 120 C yielded (M+NH 4 ) + and (M+H‐RCO 2 H) + ions of high abundance or as base peak, thereby indirectly indicating the molecular weights of the ester and the sterol and acid moieties. Ammonia CI spectra of all esters containing a Δ 5 ‐sterol moiety exhibited in addition to the above 2 ions an M+NH 4 ‐RCO 2 H fragment. At a source block temperature of 150 C, M+H‐RCO 2 H fragment was the base peak for all esters, and there was little or no indication of an (M+NH 4 ) + adduct ion. Protonated molecules were not observed for any esters analyzed by methane or isobutane CI. Molecular ions of 3–14% intensity were obtained for only 3 of the esters analyzed by electron impact; they contained a Δ 7 ‐bond in the sterol nucleus, and the acid moiety was either saturated normal or branched chain or contained a single double bond. The base peak was a function of both the acid and sterol moieties of the sterol ester. The esters containing both saturated straight chain acid and saturated sterol moieties exhibited a base peak at m/z 215. The Δ 5 ‐sterol esters with saturated branched or straight chain acid moieties exhibited base peaks at M‐RCO 2 H. Other ions also were of diagnostic value.