Analysis of 18 Polycyclic Aromatic Hydrocarbons in Soil Using the QuEChERS Method

Importance of the Topic

Polycyclic aromatic hydrocarbons are ubiquitous environmental contaminants derived from incomplete combustion of fossil fuels and organic matter. Many PAHs are classified as carcinogenic, mutagenic, or teratogenic, posing significant risks to human health and ecosystems. Reliable detection of PAHs in soil is essential for environmental monitoring, regulatory compliance, and risk assessment.

Objectives and Study Overview

This study demonstrates a streamlined sample preparation protocol using the QuEChERS method for the extraction and quantification of 18 key PAHs in soil matrices. It evaluates analytical performance parameters including recovery, reproducibility, linearity, and chromatographic separation using a specialized GC column.

Methodology and Instrumentation

The procedure involves two main stages: extraction and clean-up.

• Extraction stage: Five grams of sieved soil are hydrated, spiked with PAH standards, then extracted with acetonitrile in the presence of a salt mixture of magnesium sulfate and sodium chloride. Samples are vortexed and centrifuged to separate the organic phase.
• Dispersive SPE clean-up: A portion of the acetonitrile extract is transferred to a tube containing sorbents including magnesium sulfate and primary secondary amine silica, which remove matrix interferences. The cleaned extract is centrifuged and transferred to vials for GC-MS analysis.
• Quantitation: Calibration standards ranging from 50 to 2000 ng/mL are prepared with deuterated internal standards. GC-MS analysis is performed in selected ion monitoring mode to enhance sensitivity.

Main Results and Discussion

• Chromatographic separation: The low-bleed TraceGOLD TG-17SilMS column achieved baseline resolution of critical PAH pairs and isobaric compounds such as benzofluoranthene isomers.
• Linearity: Calibration curves showed coefficients of determination greater than 0.997 for all analytes across the tested range.
• Recoveries and precision: Average recoveries for 18 PAHs spiked at 1 mg/kg ranged from 85.0 to 106.7 percent, with relative standard deviations between 0.3 and 2.8 percent over six replicates.

Benefits and Practical Applications

The QuEChERS-based workflow offers several advantages:

• Speed: Up to eight samples can be processed in under 30 minutes.
• Cost efficiency: Minimal solvent volumes and reduced sorbent requirements lower operational expenses.
• Simplicity: Fewer handling steps reduce potential for error and contamination.
• Versatility: Effective extraction of both polar and nonpolar compounds without chlorinated solvents.

Future Trends and Potential Applications

The approach may be extended to other hydrophobic organic pollutants, high-molecular-weight PAHs, or diverse environmental matrices. Coupling with high-resolution mass spectrometry or omics platforms can enhance identification of unknowns. Miniaturized and field-deployable QuEChERS kits may facilitate on-site screening for rapid environmental decision making.

Conclusion

The QuEChERS sample preparation combined with GC-MS analysis on a TraceGOLD TG-17SilMS column provides a robust, reproducible, and sensitive method for quantifying 18 PAHs in soil. High recoveries, excellent precision, and strong linearity demonstrate its suitability for routine environmental monitoring and regulatory compliance.

Instrument Used

• Gas chromatograph equipped with TraceGOLD TG-17SilMS capillary column
• Thermo Scientific TRACE GC Ultra system
• Thermo Scientific ISQ mass spectrometer operating in electron ionization SIM mode
• Thermo Scientific TriPlus RSH autosampler
• Data processed with Thermo Scientific XCalibur software

References

1. M Anastassiades, SJ Lehotay, D Stajnbaher, FJ Schenck, Journal of AOAC International 86 (2003) 412