Determination of Polycyclic Aromatic Hydrocarbons (PAHs) and Aliphatic Hydrocarbons in Oysters by GC-MS/MS

Significance of the Topic

The accurate determination of polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons in oyster tissue is essential for food safety monitoring and environmental impact assessment following marine oil spills. PAHs are known carcinogens, and the hydrocarbon profile helps trace contamination sources and protect public health.

Objectives and Study Overview

This method describes a combined analytical workflow to extract, clean up, and quantify 16 priority PAHs along with aliphatic hydrocarbons in oysters. It is designed to screen for contamination levels, compare profiles with Gulf of Mexico crude oil, and provide semi-quantitative data on PAH concentrations relative to regulatory limits.

Methodology and Instrumentation

The procedure involves:

• Homogenizing oyster meat and weighing 2 g aliquots with isotopically labeled internal standards.
• Performing liquid extraction using hexane in an ultrasonic bath, repeated four times, followed by centrifugation.
• Cleansing extracts on silica-based SPE cartridges and eluting with hexane.
• Evaporating to dryness under nitrogen and reconstituting in cyclohexane with surrogate standards.
• Injecting the final extract into a GC-MS/MS system for simultaneous full-scan profiling of aliphatic hydrocarbons and SRM quantification of PAHs.

Instrumentation Used

Main analytical instruments include:

• Thermo Scientific TRACE GC Ultra gas chromatograph coupled to a TSQ Quantum XLS triple quadrupole mass spectrometer.
• ULTRA-TURRAX dispersing tool and ultrasonic bath for sample homogenization and extraction.
• Vacuum evaporator and nitrogen blow-down apparatus for concentration steps.
• Heraeus Multifuge X3 centrifuge and Thermo Scientific SPE vacuum manifold.

Main Results and Discussion

Method performance showed:

• Aliphatic hydrocarbon recoveries ranged from 52 % (lower C-chain losses) to 108 % (C-16 to C-34 range).
• Higher-mass PAHs (e.g., benzo[a]pyrene, chrysene) exhibited recoveries of 65–126 %; lower-mass PAH recoveries could not be fully assessed due to background contamination.
• Limits of detection were 20–100 ng/g for aliphatic hydrocarbons (full-scan) and 1–7 ng/g for higher-mass PAHs (SRM mode).
• Specificity was confirmed by matching retention times, ion ratios of quantifier/qualifier transitions, and full-scan spectral patterns.
• Hydrocarbon profiles of spiked oyster samples aligned closely with Gulf of Mexico crude oil fingerprints, supporting source identification.

Benefits and Practical Applications

The method provides a rapid, rugged screening approach for regulatory laboratories, enabling:

• Semi-quantitative assessment of PAH contamination to flag samples exceeding safety thresholds.
• Hydrocarbon fingerprinting for environmental forensics and spill source attribution.
• Adaptation for quality control in seafood safety programs and industrial monitoring.

Future Trends and Potential Applications

Advancements may include:

• Integration of high-resolution mass spectrometry for improved sensitivity and accurate mass confirmation of low-mass PAHs.
• Automated sample preparation workflows and on-site portable GC-MS units for rapid field screening.
• Extension to other marine species and complex food matrices for broader environmental surveillance.

Conclusion

This GC-MS/MS protocol offers a comprehensive solution for detecting and profiling PAHs and aliphatic hydrocarbons in oysters. With validated recoveries, detection limits, and source-matching capabilities, it supports food safety decisions and environmental forensic investigations.

References

• NIST Standard Reference Material® 1582, Petroleum Crude Oil.
• NIST Standard Reference Material® 1494, Aliphatic Hydrocarbons in 2,2,4-Trimethylpentane.
• Dr. Ehrenstorfer 5-Methylchrysene standard.