Structural characterization of steranes and hopanes in petroleum by ion mobility mass spectrometry

The structural characterization of hydrocarbon biomarkers with high molecular weight still remains a challenge even using the ultrahigh resolution mass spectrometry (UHRMS). In this work, a homologue series identification strategy was proposed based on the "sequentiality" of crude oil, where "sequentiality" revealed a compositional continuum of the naturally existing components in crude oil. With the steady increase of mass to charge ratio (m/ z), the collision cross-section (CCS) value was measured by trapped ion mobility mass spectrometry (TIMS-MS) and showed a linear relationship with m/z. The structure of C20-C34 steranes and C27-C38 hopanes was determined using linear correlation. The accuracy of molecular formula was confirmed by UHRMS, and the structural determination was verified by MS/MS. The identification of sterane series and hopane series demonstrated the application of the homologue series identification strategy in the structural determination of hydrocarbon biomarkers with high molecular weight. Compared with gas chromatography-mass spectrometry (GC-MS) within the GC-able reach, the new analytical strategy showed better qualitative results and comparable quantitative results, which made it promising to explore novel hydrocarbon biomarkers in crude oil.