Assessing Biodegradation of Brazilian Crude Oils via Characteristic Profiles of O₁ and O₂ Compound Classes: Petroleomics by Negative-Ion Mode Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Profiles for polar heteroatom compounds were obtained via Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) using electrospray ionization (ESI) in negative-ion mode for a set of 30 Brazilian oil samples from distinct sedimentary basins and used to estimate biodegradation extents. The samples were initially subjected to traditional geochemical biodegradation analysis to classify them in term of biodegradation levels as based on the Peters and Moldowan scale (PM scale). When the profiles were correlated with the PM scale, it was found that the O₁, N, NO₂, NO₃, and N₃O₂ classes decrease, whereas the O₂, O₃, and O₄ classes increase in relative abundance with biodegradation. The acyclic to cyclic acids (A/C) ratio of the O₂ class, mainly composed of naphthenic acids, provided a robust parameter to classify biodegradation levels of Brazilian oils. A modified saturated acid (SA) index was also used to classify biodegradation levels. For the O₁ class, two new monoaromatic (MA) indexes were proposed to predict the biodegradation extent. These MA parameters are based on the most readily degraded phenolic and/or benzylic O compounds by microorganisms and the persistence of O compounds with higher double bond equivalent (DBE) values in more degraded oils