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

Abstract

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 O 1, S 1 O 1, O 2, S 1 O 2, S 2 O 2, O 3, S 1 O 3, O 4, S 1 O 4, N 1, N 1 O 1, N 1 O 2, N 1 S 1, and S 1 classes, while the polar NSO compounds in asphaltene fractions contain O 1, S 1 O 1, S 2 O 1, O 2, S 1 O 2, S 2 O 2, O 3, S 1 O 3, S 2 O 3, O 4, S 1 O 4, S 2 O 4, O 5, S 1 O 5, S 2 O 5, O 6, N 1, N 1 O 1, N 1 O 2, N 1 O 3, N 1 S 1, and N 2 classes. Polar NSO compounds with stronger molecular polarity and larger molecular weight are readily fractionated into asphaltene fractions. The O 2 class is prevalent in polar NSO compounds of both maltene and asphaltene fractions of all bitumen samples. The N 1 class in maltene fractions is dominated by compounds with DBE values of 9, 10, 12 and 13, while the N 1 class in asphaltene fractions is dominated by compounds with a DBE of 15. Most of these N 1 compounds are likely pyrrolic compounds with various numbers of aromatic rings. The biodegradation pathways of nitrogen-containing compounds are also explored in this study. N 1 species are likely converted to N 1 O 1 and N 1 O 2 species following biodegradation pathways such as ring-opening reaction or carbazole dioxygenase (CARDO) catalytic oxidation reaction. S 1 O 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.