Application of a Low-Cost Adsorbent in the Chromatographic Separation and Enrichment of Biomarkers for GC-C-IRMS Analysis

Organic geochemistry relies on biomarkers, such as hopanes and steranes, to assess origin, thermal maturity, and oil–source rock correlation. However, the isolation and enrichment of these compounds using conventional chromatography – typically based on commercial silica and alumina – have limitations in selectivity and resolution that can compromise subsequent GC-C-IRMS analyses. In this context, novel mineral stationary phases represent a promising strategy to improve the separation of saturated biomarkers. Structural, polarizability, and conformational differences among these compounds lead to distinct degrees of interaction with mineral surfaces, favoring fractionation through selective adsorption. In this study, modified aluminosilicate was evaluated as a stationary phase for the separation and enrichment of saturated petroleum biomarkers, using a hexane/ethyl acetate elution gradient. Because of its availability, chemical stability, and surface properties, the performance of this material was compared with that of conventional adsorbents. Three oil samples (A, B, and C) provided by CENPES/PETROBRAS, with distinct origins and degrees of biodegradation, were subjected to deasphalting and chromatographic fractionation using the solid stationary phase under an elution gradient. Molecular characterization of the oils revealed a complex geochemical signature, ranging from lacustrine (freshwater to saline) to marine depositional environments. The consistent occurrence of dinosteranes derivatives evidenced dinoflagellate contributions under eutrophic conditions, indicating marine influence even in predominantly lacustrine samples. Regarding biodegradation levels, the samples were classified on the Peters and Moldowan scale as PM0 (Oil B), PM3 (Oil A), and PM5 (Oil C).The biodegradation ranks for oil samples were attributed as pristine to moderate based on the low abundance of 25-norhopane and preserved molecular parameters of terpanes and steranes.Chromatographic fractionation using the alternative stationary phase enabled the selective separation and enrichment of saturated biomarkers, including tricyclic terpanes, hopanes, and low-abundance compounds such as dinosteranes and gammacerane. These results demonstrate the potential of this natural solid adsorbent as a low-cost, easily prepared stationary phase with reduced solvent consumption, providing a viable alternative for the pre-fractionation of oils across varying biodegradation levels prior to subsequent isotopic analyses by GC-C-IRMS.