Gel permeation chromatography for fractionation and isotope ratio analysis of steranes and triterpanes in oils

Gel permeation chromatography (GPC) was applied to concentrate steranes and triterpanes in oils and measure their compound-specific carbon isotope ratios (δ13C). Trace steranes and triterpanes were concentrated from n-alkane-rich Miocene Yabase marine oils by GPC. δ13C was determined by gas chromatography–combustion/isotope ratio–mass spectrometry (GC–C/IR–MS). The δ13C of cholestane from the Yabase oil ranges from −24.4 to −26.3‰. This is nearly consistent with that of the n-C18 to n-C20 alkanes, suggesting significant algal and zooplankton contribution. The δ13C of ethylcholestane from the Yabase oil is comparatively light, ranging from −26.7 to −30.8‰. It is similar to the δ13C of n-C27, n-C29, n-C31 alkanes and oleanane, suggesting a significant contribution of terrestrial higher plant material.