Simultaneous determination of compound‐specific isotopic compositions of acyclic isoprenoids and n‐alkanes in light crude oil

Abstract

Stable carbon and hydrogen isotope ratios of individual n‐alkanes and acyclic isoprenoids are important tools in petroleum geochemistry. However, the analysis requires baseline separation and peak profiles using gas chromatography–isotope ratio mass spectrometry to obtain accurate compound‐specific isotope data. Time‐consuming isolation or purification is typically conducted to separate the compounds to avoid co‐elution with other compounds or matrices in crude oils. We developed a simple gas chromatography separation method to simultaneously measure the compound‐specific carbon or hydrogen isotope compositions of n‐alkanes and acyclic isoprenoids. It was achieved by direct injection of the whole crude condensate and light oil or the saturated fractions of different types of crude oils using a 60 m DB‐17ms column. This method simplifies the pre‐treatment of compound‐specific isotope analysis, saves manpower and time, and reduces the use of organic solvents to be more environmentally friendly.