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

Significance of the topic

The 2010 Gulf of Mexico oil spill prompted the use of nearly one million gallons of COREXIT dispersants to mitigate environmental impact. Monitoring residual levels of these formulations in seawater is essential to assess risks to human health, wildlife, and coastal ecosystems. Robust analytical methods enable accurate quantitation and support long-term environmental studies.

Objectives and study overview

This work presents analytical workflows for detecting and quantifying the two primary oil dispersant formulations, COREXIT 9500 and 9527, in seawater. It covers direct GC/MS injection versus solid-phase extraction cleanup for glycol solvents and LC/MS/MS approaches for both glycols and the anionic surfactant marker bis(2-ethylhexyl) sulfosuccinate (AOT).

Methodology and instrumentation

• Sample cleanup via Strata-X-A solid-phase extraction to remove salts and matrix interferences.
• GC/MS on an Agilent 6890 GC coupled to a 5973 MS, using a Zebron ZB-WAXPLUS column in SIM mode for glycols.
• LC/MS/MS on an AB Sciex API 4000 triple quadrupole with Agilent 1200 SL UHPLC, using Kinetex PFP and C8 core-shell columns in MRM mode.
• Timed polarity switching to detect 2-butoxyethanol in positive ESI and AOT in negative ESI within a single LC run.

Main results and discussion

• Direct seawater injection caused salt buildup and unstable calibration; SPE cleanup eliminated these issues and reduced maintenance frequency.
• GC/MS method achieved recoveries >96% for 2-butoxyethanol and propylene glycol in 1 mL seawater spiked at 5 ppm, with RSD <2% and detection limits ≈1 ppm.
• LC/MS/MS using a Kinetex C8 column produced sharp 5–6 s peaks and low-ppb detection for AOT; use of a deuterated internal standard improved calibration linearity (R² > 0.9998).
• Simultaneous LC/MS/MS elution of AOT and 2-butoxyethanol was achieved on a PFP phase with ~1 min separation and reliable polarity switching.

Benefits and practical applications of the method

• Sensitivity at low ppb–ppm levels supports environmental monitoring of dispersant residues.
• High-speed chromatography and streamlined SPE sample prep increase laboratory throughput.
• Improved instrument uptime through effective matrix cleanup.
• Complementary GC/MS and LC/MS/MS strategies provide a comprehensive profile of dispersant markers.

Future trends and possibilities

• Application of these methods to sediments, biota, and tissue samples for broader environmental assessment.
• Development of derivatization or novel stationary phases to enable GC/MS analysis of acidic surfactants.
• Expansion of isotopically labeled standards to improve quantitation of all target analytes.
• Integration with high-resolution mass spectrometry for non-target screening of transformation products.

Conclusion

The combined GC/MS and LC/MS/MS workflows deliver complementary, sensitive, and reliable tools for detecting key dispersant components in seawater. These approaches aid environmental impact assessments and regulatory monitoring following large-scale oil spills.

Used instrumentation

• Agilent 6890 GC with 5973 MS detector
• Agilent 1200 SL UHPLC
• AB Sciex API 4000 LC/MS/MS system
• Zebron ZB-WAXPLUS GC columns
• Kinetex PFP and C8 core-shell LC columns
• Strata-X-A solid-phase extraction cartridges

References

1. National Incident Command’s Flow Rate Technical Group, Flow Rate Report on Gulf of Mexico oil spill, 2010.
2. Environmental Protection Agency, monitoring guidelines for oil dispersants.
3. Nalco Company, Composition data for COREXIT 9527 and 9500, accessed 2010.