Adduct-Ion Removal and Fractionation Reveal Sulfoxide-Derived Compounds in High-Sulfur Crude Oils by FT-ICR MS

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has greatly promoted an understanding of the complex chemical composition of petroleum-derived samples. Relying on this analytical instrument, along with pretreatment methods such as component separation, virtually comprehensive approaches for petroleum molecular composition analysis have been established in the past two decades. However, for certain samples, specific pretreatments and instrumental settings may be required for FT-ICR MS analysis. In this study, specific compound species, including Na1O2S2, Na1O4S1, N1O 2S1, and Na1O1S1, that are not commonly found in petroleum were identified in two high-sulfur-content crude oils using positive-ion electrospray ionization (+ESI) FT-ICR MS. Collision-induced dissociation (CID) was employed to further characterize these species, and they were confirmed to be sulfoxide-derived adducts. Ionization additives and broadband CID were combined, enabling the elimination of all types of adduct ions. Additionally, the crude oils were separated into multiple subfractions by a chromatographic column with cross-polarity elution, and the subfractions were analyzed separately incorporating the proposed adduct elimination method. High-condensation O1S1 class species, which had not been detected in direct analysis, were identified in subfractions. The adduct ion elimination method and the cross-polarity chromatographic approach demonstrated great applicability across different crude oils, providing a viable strategy for the correct classification of compound types and the identification of components that had been overlooked due to matrix effect and ionization suppression.