Molecular characterization of condensates altered by thermochemical sulfate reduction and evaporative fractionation using high-resolution mass spectrometry

Abstract

Conventional biomarkers are least available for the origin and formation mechanism investigation in condensates due to their extremely low concentrations. Heteroatomic compounds in condensates can provide unique insights for their origin and formation, but these compounds are with the low separation ability by conventional mass spectrometry tools. They can be characterized with the advance of the high-resolution mass spectrometry, but few study focuses on the altered condensate oil and their molecular-level compositions. In this study, a total of 19 condensates are analyzed to study the effects of thermochemical sulfate reduction and evaporative fractionation on the changes of molecular compositions characterized by Orbitrap mass spectrometry. The results show that thermochemical sulfate reduction (TSR) make the oils considerably enriched in S₁ species (sulfur-containing compounds with one sulfur atom) (>90 %) and depleted in CH₂s species (hydrocarbons compounds) (<3%) relative to the non-TSR altered oils due to the consumption of hydrocarbon and yield of sulfur-containing compounds. Relatively abundant S₁ species with low DBE (Double Bond Equivalent) values (0–3) likely corresponding to thiols and thioethers in TSR-altered oils. However, the relative abundance of CH₂s species in the oils undergoing evaporative fraction are much higher than that in non-evaporative fraction altered oils leading by the strong solubility of hydrocarbon in gas. Therefore, the relative contents of heteroatomic compounds are significant for the TSR alteration and evaporative fraction definition of condensates and their origin investigation.