Puspa L. Adhikari, Roberto L. Wong, Edward B. Overton

Accurate characterization of petroleum hydrocarbons in complex and weathered oil residues is analytically challenging. This is primarily due to chemical compositional complexity of both the oil residues and environmental matrices, and the lack of instrumental selectivity due to co-elution of interferences with the target analytes. To overcome these analytical selectivity issues, we used an enhanced resolution gas chromatography coupled with triple quadrupole mass spectrometry in Multiple Reaction Monitoring (MRM) mode (GC/MS/MS-MRM) to eliminate interferences within the ion chromatograms of target analytes found in environmental samples. This new GC/MS/MS-MRM method was developed and used for forensic fingerprinting of deep-water and marsh sediment samples containing oily residues from the Deepwater Horizon oil spill. The results showed that the GC/MS/MS-MRM method increases selectivity, eliminates interferences, and provides more accurate quantitation and characterization of trace levels of alkyl-PAHs and biomarker compounds, from weathered oil residues in complex sample matrices. The higher selectivity of the new method, even at low detection limits, provides greater insights on isomer and homolog compositional patterns and the extent of oil weathering under various environmental conditions. The method also provides flat chromatographic baselines for accurate and unambiguous calculation of petroleum forensic biomarker compound ratios. Thus, this GC/MS/MS-MRM method can be a reliable analytical strategy for more accurate and selective trace level analyses in petroleum forensic studies, and for tacking continuous weathering of oil residues.