Simultaneous routine GC-MS analysis of PCBs, PAHs, and their derivatives in soil using modified QuEChERS methodology

Importance of the Topic

Persistent organic pollutants such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) pose significant environmental and health risks due to their toxicity, lipophilicity, and resistance to biodegradation. Substituted derivatives—including oxy-PAHs, methyl-PAHs, and nitrogen/sulfur heterocycles (NSO-PAHs)—often exhibit equal or greater toxicity, making comprehensive soil monitoring essential for protecting ecosystems and human populations.

Aims and Overview

This study evaluates the quantitative performance of the Thermo Scientific ISQ 7000 single quadrupole GC-MS system, equipped with the ExtractaBrite electron ionization source and NeverVent™ Technology, for simultaneous routine analysis of 45 target analytes (16 EPA PAHs, 7 marker PCBs, 3 oxyPAHs, 10 methyl-PAHs, and 9 NSO-PAHs) in soil using a modified QuEChERS sample preparation.

Methodology and Instrumentation

Modified QuEChERS extraction:

• Freeze-dry and sieve soil, spike with 13C/2H internal standards at 50 ng/g.
• Extract with 20 mL DCM:acetone (1:1), salt out with MgSO4/NaCl/citrate, shake and centrifuge.
• dSPE cleanup with MgSO4 and PSA, evaporate under N2, reconstitute to 1 mL in n-hexane spiked with triphenyl phosphate.
• Total prep time: ~2 hours.

GC-MS analysis:

• Autosampler: AI/AS 1310, GC: TRACE 1310 with TraceGOLD TG-5 SilMS column (30 m × 0.25 mm × 0.25 μm).
• MS: ISQ 7000 single quadrupole with ExtractaBrite EI source and NeverVent Technology for <2 min vent-free maintenance.
• Timed-SIM acquisition, 20 min run time, helium carrier gas, SSL injection at 300 °C.
• Data processing via Chromeleon CDS with eWorkflows for automated calibration and reporting.

Main Results and Discussion

Chromatography:

• Complete separation of critical PAH/PCB pairs in <20 min.
• Sharp, symmetric peaks even for high-boiling compounds (e.g., benzo[ghi]perylene BP 550 °C).

Sensitivity and quantitation:

• Instrument detection limits (IDLs) from 60 to 2000 fg on column (0.06–2.00 μg/kg in soil), with RSD <15% at 99% confidence.
• Limits of quantification (LOQs) between 0.4 and 5.0 μg/kg in soil, ion ratio deviation ±30%, area RSD <15%.
• Linearity over 0.1–500 pg/μL (0.1–500 μg/kg) with R2 ≥ 0.998 and response factor RSD <10%.

Recovery and precision:

• Mean internal standard recovery ~75%, seven replicates RSD <15% (most <5%).

Selectivity and carryover:

• SIM analysis in complex soil matrix showed minimal interference.
• No detectable carryover using mixed needle wash (DCM:toluene:n-nonane).

Incurred residues:

• Low-level PCBs and PAHs quantified in real soil (e.g., PCB-153 at 0.87 μg/kg) with ion ratio deviations <2%.

Benefits and Practical Applications

By consolidating multiple compound classes into a single workflow, this method offers:

• High throughput: up to 4× faster chromatographic runs and 10–20× faster sample preparation versus Soxhlet.
• Cost-effectiveness: reduced solvent use and labor.
• Robust routine performance: rapid vent-free column/source changes and automated data handling.

Future Trends and Potential Uses

Environmental laboratories may extend this approach to emerging contaminants and higher-order derivatives, integrate robotics for sample handling, and apply machine learning for complex data deconvolution. Miniaturized GC-MS and field-deployable workflows could further enhance on-site monitoring of soil and other matrices.

Conclusion

The combination of modified QuEChERS extraction with the ISQ 7000 GC-MS and NeverVent Technology delivers a fast, sensitive, and reliable method for simultaneous analysis of PCBs, PAHs, and derivatives in soil. Its high throughput, reproducibility, and low detection limits make it ideal for routine environmental monitoring and quality control.

Reference

1. CEN/TR 16998:2016 Ambient air – report on nitro- and oxy-PAHs.
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4. Thermo Sci. Tech. Note 10721, 2019.
5. Thermo Sci. App. Note 21735, 2017.