Comparison and Application of Gas Chromatography–Mass Spectrometry and Gas Chromatography–Tandem Mass Spectrometry for the Determination of Sterane and Terpane Compounds in Petroleum Geological Samples

Sterane and terpane compounds are key biomarkers in petroleum geochemistry to identify organic matter sources, depositional environments, and thermal evolution. The reliability of their analysis directly affects the accuracy of oil-source correlation and maturity assessment. This study addresses the limitations of conventional GC-MS, including co-eluting peak interference and limited quantitative accuracy in complex matrices. Source rocks and crude oils from the Huagang Formation in the Xihu sag were analyzed to compare GC-MS and GC-MS/MS in characterizing sterane and terpane parameters and their diagnostic significance. Using single ion monitoring (SIM) and selected reaction monitoring (SRM) to obtain parameters, sterane triangular plots and ratio parameters were employed for comprehensive evaluation. Results showed consistent identification of organic matter sources, indicating mixed-source input dominated by lower aquatic organisms. The average differences in heterocyclic sterane parameters measurements including C₂₉-20S/(20S + 20R), C₂₉-αββ/(ααα + αββ), and C₂₇-αββ/(ααα + αββ) were all less than 0.05, with overall trends consistent across both methods. Notably, GC-MS/MS yielded C₂₉-20S/(20S + 20R) values closer to the evolutionary endpoint (~0.55), which aligned better with the measured vitrinite reflectance (R_o) values (0.84%–1.40%). For terpane parameters, GC-MS/MS showed an average Ts/Tm value approximately 0.18–0.28 higher than GC-MS, and a lower Ga/C₃₀H value by approximately 0.11–0.12, yet both methods maintained consistency in depositional environment identification and maturity trends. In conclusion, while GC-MS remains valuable for routine sterane and terpane analysis, GC-MS/MS offers higher accuracy in maturity assessment for high maturity or complex matrix samples by enhancing selectivity and resolution, providing more reliable technical support for fine-scale geochemical analysis of sterane and terpane compounds.