Molecular Characterization of Hydrocarbons in Petroleum by Ultrahigh-Resolution Mass Spectrometry

Abstract

The progress in ultrahigh-resolution mass spectrometry (UHRMS) and related technologies has significantly promoted the development of petroleomics. The study of petroleomics has greatly broadened our knowledge of the composition of petroleum at the molecular level, especially heavy fractions that cannot be analyzed by gas chromatography (GC)-based methods. To date, heteroatom-containing (O, N, S, and metal atoms) compounds in petroleum have been studied extensively by UHRMS. Nevertheless, the main components of petroleum, hydrocarbon compounds, have remained out of reach of petroleomics characterization for a long time because they are too difficult to be softly and efficiently ionized for UHRMS analysis. It is undoubtedly the case that petroleum hydrocarbons should not be the missing part of petroleomics characterization since they play important roles not only as feeding pools for various high value-added petroleum products but also as critical biomarkers for geochemistry studies. Here, the most recent breakthroughs in petroleomics characterization of hydrocarbon compounds using UHRMS rather than conventional methods have been reviewed. Innovations of soft ionization methods can transform non-polar hydrocarbon molecules into molecular ions or quasi-molecular ions that are reachable for UHRMS without fragmentation. The development of data processing methods has assisted the decoding of the complicated UHRMS data to visualize the molecular composition and structure of hydrocarbon compounds. These advances make it possible to see the whole picture of petroleum compositions, from light distillation fractions to heavy distillation fractions, and from small volatile molecules to large non-volatile ones. The applications of UHRMS-based methods for petroleomics characterization of hydrocarbon compounds in crude oils and various petroleum samples including fuel oil, slurry, and even asphaltene have made a great contribution to petrochemistry and geochemistry studies, especially in the fields of molecular refining and biomarker discovery.