Oil Oxidative Transformation Products Revealed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

The chemical transformation of petrogenic carbon in the environment yields an incredible complex mixture of products that can dramatically alter native petroleum chemical functionalities. The changes affect toxicity, solubility, tendency for emulsion/mousse formation, aggregation, and ultimately, bioavailability. However, these changes are difficult to track at the molecular level, as the qualitative understanding of the (predominately) oxidative weathering is hampered by the immense complexity of the unaltered oil and multiplicative increase in complexity post-oxidation. Simply, a large fraction of unaltered oil that was initially accessible by GC-methods is chemically transformed into species that preclude GC based analyses. Thus, the fate of petrogenic transformation products and their potential to form undesirable future contaminants remain unknown. However, recent advances in analytical methodology and instrumentation now allow a molecular-level insight into these complex systems. Combined with the comprehensive analysis of the unaltered well oil, detailed compositional analysis of oil-impacted sites along the Gulf of Mexico coast over the past 4 years has revealed tens-of-thousands of previously unidentified, unique, biotic and abiotic transformation products that persist. Here, we highlight efforts to characterize oxidized transformation products, identify their oxygen functionalities, and demonstrate how they affect physical/chemical behavior of weathered oil. Temporal analysis of field samples reveal compositional changes of weathered oil as a function of oil contamination levels. Once determined, abiotic microcosm results are compared to the field samples to assess how well they account for observed changes in field samples. Finally, chromatographic separation of unaltered well oil (and surrogate) into structurally defined fractions (saturate, 1-ring, 2-ring, 3-ring, 4-ring and 5+ring aromatics / polars), followed by subsequent photo-oxidation of each, reveal the importance of the individual structural motifs to transformation products identified in field samples. Work supported by NSF Division of Materials Research through DMR-11-57490, BP/The Gulf of Mexico Research Initiative to the Deep-C Consortium, Future Fuels Institute, and the State of Florida.