Acidic and Neutral Polar NSO Compounds in Heavily Biodegraded Oils Characterized by Negative-Ion ESI FT-ICR MS

Five heavily biodegraded tar sand bitumens from an oil column were separated into maltene and asphaltene fractions for analysis by negative-ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). These bitumens have an identical source, which have experienced a natural sequence of biodegradation. The polar NSO compounds in maltene fractions contain O₁, S₁O₁, O₂, S₁O₂, S₂O₂, O₃, S₁O₃, O₄, S₁O₄, N₁, N₁O₁, N₁O₂, N₁S₁, and S₁ classes, while the polar NSO compounds in asphaltene fractions contain O₁, S₁O₁, S₂O₁, O₂, S₁O₂, S₂O₂, O₃, S₁O₃, S₂O₃, O₄, S₁O₄, S₂O₄, O₅, S₁O₅, S₂O₅, O₆, N₁, N₁O₁, N₁O₂, N₁O₃, N₁S₁, and N₂ classes. Polar NSO compounds with stronger molecular polarity and larger molecular weight are readily fractionated into asphaltene fractions. The O₂ class is prevalent in polar NSO compounds of both maltene and asphaltene fractions of all bitumen samples. The N₁ class in maltene fractions is dominated by compounds with DBE values of 9, 10, 12 and 13, while the N₁ class in asphaltene fractions is dominated by compounds with a DBE of 15. Most of these N₁ compounds are likely pyrrolic compounds with various numbers of aromatic rings. The biodegradation pathways of nitrogen-containing compounds are also explored in this study. N₁ species are likely converted to N₁O₁ and N₁O₂ species following biodegradation pathways such as ring-opening reaction or carbazole dioxygenase (CARDO) catalytic oxidation reaction. S₁O_2–5 classes are identified as the dominant sulfur-containing compound classes under negative-ion ESI mode. These classes are considered to contain acid functionalities with higher polarity because the sulfur-containing compounds without oxygen are difficult to analyze by negative-ion ESI in which acids can be ionized by deprotonation. Both progressive oxidation and sulfuration may be involved in the anaerobic biodegradation of sulfur-containing acidic compounds.