Dioctyl sulfosuccinate analysis in near-shore Gulf of Mexico water by direct-injection liquid chromatography–tandem mass spectrometry

Dioctyl sulfosuccinate (DOSS) was a major component of the dispersants most used in the 2010 Deepwater Horizon Oil Spill incident response. This analytical method quantifies salt water DOSS concentrations to a reporting limit of 20 μg/L, which was below the United States Environmental Protection Agencyʹs (U.S. EPA) 40 μg/L DOSS Aquatic Life Benchmark. DOSS in Gulf of Mexico water samples were analyzed by direct-injection reversed-phase liquid chromatography–tandem mass spectrometry (LC–MS/MS). Sample preparation with 50% acetonitrile (ACN) enabled quantitative transfer of DOSS and increased DOSS response 20-fold by reducing aggregation. This increased sensitivity enabled the detection of a confirmatory transition over the calibration range of 10–200 μg/L. U.S. EPA Region 5 and Region 6 laboratories analyzed hundreds of near-shore surface Gulf of Mexico water samples, none contained more than the 20 ppb reporting limit. The matrix spike DOSS/deuterated surrogate (DOSS-D34) correlation of determination varied with mobile phase modifier (ammonium formate R2 = 0.95 and formic acid R2 = 0.27). Using ammonium formate, DOSS-D34 accurately measured DOSS matrix effect. The near-shore sodium concentrations varied more than 10,000-fold, but were not strongly correlated with DOSS recovery. DOSS detection by LC–MS/MS enabled rapid analysis which was valuable in guiding incident response.