Fingerprinting Deepwater Horizon Oil in the northern Gulf of Mexico using biomarkers and Gas Chromatography-Triple Quadrupole Mass Spectrometry (GC/MS/MS)

Petroleum biomarkers such as hopanes, steranes, and triaromatic steroids are more persistent than alkanes and aromatic compounds. Thus, they are often used to track spilled oil in the environments and as a proxy for weathering processes. The present study utilizes water samples, suspended and sinking particles, and seafloor sediments collected during 2011-2013 from various locations of the northern Gulf of Mexico with wide range of contaminated oil for Deepwater Horizon (DWH) oil fingerprinting. The MC252 source oil along with the samples collected in this study were analyzed using a gas chromatography coupled with a triple quadrupole mass spectrometry (GC/MS/MS) in Multiple Reaction Monitoring (MRM) mode and the results were compared with results from commonly used GC/MS selective ion monitoring (SIM) method. The results indicate that the MRM method separates interfering ions from interfering compounds and can be a powerful analytical strategy for a reliable identification and determination of trace levels of biomarkers in complex matrices. Source indicators such as the MRM fragment ion chromatograms of the biomarkers and their diagnostic ratios in samples were compared with the MC252 source oil. The preliminary results show that the biomarkers were below detection limits in dissolved samples. However, in few particulate and seafloor sediment samples, primarily from the immediate vicinity of the Macondo wellhead, contained their patterns. The results also illustrate that these biomarker compounds have been weathered within 1-3 years following the oil spill, and their DWH oil signature in some of these samples reflects this weathering.