"Novel Applications of Mass Spectrometry to Atmospheric Chemistry"
Professor Kerri Pratt, University of Michigan, Department of Chemistry
"Elucidation of biodegradation products and rates of Corexit9500 in seawater using High Resolution Mass Spectroscopy"
Sarah Choyke, Laboratory of Professor Lee Ferguson, Duke University, Department of Chemistry
High-resolution mass spectrometry has emerged as a powerful analytical tool for investigating the fate and transport of organic contaminants in environmental samples. Recent advances in resolving power, mass accuracy, and acquisition rates have allowed for improved approaches in non-target and suspect contaminant screening, transformation product identification, and increased certainty in identification and quantitation of trace organic compounds. Despite these advances, the analysis of environmental samples impacted by surfactants often suffers from signal suppression and poor chromatographic separation due to co-eluting peaks and matrix-interferences. These factors can be mitigated by incorporating high performance liquid chromatography (HPLC) and electrospray ionization (ESI) to acquire high quality data. These data can be analyzed using a suspect contaminant screen to tentatively identify ethoxymers by homologue series, accurate mass, tandem MS/MS, and retention time. Transformation pathways can also be identified using suspect screening, tandem MS/MS, mass defect, isotopic patterns, and in silico screening to achieve a comprehensive characterization of the sample and transformation products.
These workflows can be implemented to screen complex environmental samples impacted with surfactants, such as the application of Corexit series dispersants during the 2010 Deepwater Horizon Oil Spill emergency response. The use of Corexit at the wellhead and on surface oil slicks facilitated the dispersion and dissolution of crude oil into the water column and mitigated the impact of oil on sensitive coastal ecosystems. However, the fate and biotransformation kinetics and products of Corexit in seawater remained unknown. Corexit is a mixture of the anionic surfactant, dioctyl sodium sulfosuccinate, nonionic surfactants, Tween80, Tween85, and Span80, and hydrocarbon solvents. In order to study the biotransformation of the nonionic surfactant components of Corexit in seawater, I spiked Corexit9500 into coastal seawater under aerobic conditions and characterized the transformation products over time.
I observed complete ester hydrolysis of polyethoxylate sorbitan and isosorbide monoesters, and polyethoxylate fatty acid during the first 24 hours of the exposure, and complete ester hydrolysis of polyethoxylate sorbitan and isosorbide diesters and triesters over the following 10 days. Results from parallel abiotic control treatment indicated abiotic hydrolysis of the polyethoxylate monoesters in the first 4 days of the experiment while the polyethoxylate diesters and triesters remained stable for 15 days before decreasing in concentration. The identification of transformation products of Corexit9500 and its components through HRMS analysis and the measurement of associated transformation rates will lead to a better understanding of the fate, transport, and persistence of dispersants in marine environments, ultimately informing use of these materials in mitigation of future oil spills.