Molecular characterization of nonionic surfactant components of the Corexit® 9500 oil spill dispersant by high‐resolution mass spectrometry

Rationale Approximately 7 million liters of Corexit® dispersants were applied during the 2010 Deepwater Horizon oil spill to facilitate the dispersion of crude oil. At the time of application, the exact chemical composition of Corexit® was relatively unknown. Characterization of Corexit® 9500 was performed using high‐resolution mass spectrometry to further understand the complexity of the nonionic surfactant components of this mixture. Methods Corexit®9500 was analyzed by ultra‐high‐performance liquid chromatography (UHPLC) coupled to a high resolution Orbitrap Fusion Lumos mass spectrometer operated in positive electrospray ionization mode and a charged aerosol detector. Chromatographic conditions were optimized to efficiently separate isobaric and isomeric compounds. Polyethoxylated nonionic surfactants in Corexit® 9500 were identified using the following criteria: accurate mass (