Detection and Identification of Gulf Oil Dispersants (COREXIT® 9527 and 9500) by GC/MS and LC/MS/MS

Importance of the Topic

The 2010 Gulf of Mexico oil spill released millions of barrels of crude oil. Dispersants such as COREXIT® 9500 and 9527 were applied in unprecedented volumes but their environmental fate and potential impacts remain poorly understood. Reliable analytical methods are essential to detect and quantify residual dispersant components in seawater at trace levels to assess ecological and human health risks.

Objectives and Study Overview

This study presents optimized workflows for the identification and quantitation of key dispersant markers: 2-butoxyethanol (unique to COREXIT 9527), propylene glycol (common to both formulations), and bis(2-ethylhexyl) sulfosuccinate (AOT, anionic surfactant marker). The goals include achieving low detection limits in seawater, minimizing matrix interferences, and improving laboratory throughput by combining GC/MS and LC/MS/MS approaches.

Methodology and Instrumentation

• SPE Cleanup: Solid phase extraction using Strata™-X-A cartridges to remove salts and organic interferences prior to GC/MS analysis.
• GC/MS Analysis: Agilent 6890 GC coupled to a 5973 MS detector with a water-stable Zebron™ ZB-WAXPLUS™ column for separation and single-ion monitoring of glycols at low ppb levels.
• LC/MS/MS Analysis: AB Sciex API 4000 tandem mass spectrometer with Agilent 1200 UHPLC and core-shell Kinetex® columns (PFP and C8 phases). Polarity switching was employed to detect 2-butoxyethanol in positive mode and AOT in negative mode within a single run.

Results and Discussion

• Direct seawater injection caused salt buildup in the GC inlet and unstable calibration. SPE cleanup eliminated matrix effects, yielding recoveries above 96% (RSD <2%) for 2-butoxyethanol and propylene glycol at 5 ppm spike levels in 1 mL loads.
• ZB-WAXPLUS GC columns delivered sharp peaks and robust performance with water-laden samples. Detection limits approached 1 ppm by GC/MS and improved to low ppb by LC/MS/MS.
• On the Kinetex C8 column, AOT was resolved from other surfactants with peak widths of ~5 s, enabling >10 scans per peak. Calibration with a deuterated internal standard achieved R² >0.9998 across 10–500 ppb.
• A combined LC/MS/MS run on the PFP column successfully separated and quantified both AOT and 2-butoxyethanol with a ~1 min retention gap, demonstrating feasibility for multiplex monitoring.

Benefits and Practical Applications of the Method

• Accurate, sensitive detection of dispersant residues in complex seawater matrices.
• Reduced instrument downtime through effective SPE cleanup of salts.
• High-efficiency core-shell LC columns and water-compatible GC phases support fast, high-resolution separations.

Future Trends and Potential Applications

Ongoing advances may include large-volume SPE to further lower detection limits, exploration of alternative isotopic standards for challenging analytes, and integration of high-resolution mass spectrometry for non-target screening of emerging dispersant breakdown products. The described platforms can be extended to other waterborne contaminants requiring trace-level analysis.

Conclusion

The combination of SPE cleanup, aqueous-stable GC columns, and high-efficiency core-shell LC columns with tandem MS detection provides a robust toolkit for monitoring COREXIT dispersant components in seawater. These methods enhance sensitivity, precision, and laboratory productivity, supporting comprehensive environmental impact assessments following oil spills.

Reference

1. U.S. National Incident Command’s Flow Rate Technical Group. Flow Rate Technical Group Report, 2010.
2. Nalco Company. Composition of COREXIT® 9500 and 9527 as disclosed to the U.S. Environmental Protection Agency, 2010.
3. Countryman S., Trass M., Sadjadi S., Layne J. Detection and Identification of Gulf Oil Dispersants (COREXIT® 9527 and 9500) by GC/MS and LC/MS/MS. Phenomenex Application Note TN-2046, 2011.