Consolidated analysis of soil contaminants - Four-fold increase in the sample throughput with GC-Orbitrap

Significance of the topic

Monitoring persistent organic pollutants such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and their derivatives in soil is critical due to their toxicity, environmental persistence and potential for bioaccumulation. Rapid, cost-effective and high-throughput analytical workflows are essential for environmental testing laboratories to reliably assess contamination levels and protect human health.

Objectives and overview of the study

This application note describes the consolidation of multiple analyte classes (16 EPA PAHs, PCBs, oxy-PAHs, methyl-PAHs and nitrogen/sulfur/oxygen heterocycles) into a single gas chromatography–high resolution mass spectrometry (GC-HRMS) method. A modified QuEChERS extraction was combined with the Thermo Scientific Orbitrap Exploris GC system to achieve full-scan screening and targeted quantification in under 20 minutes per sample.

Methodology and instrumentation

A freeze-dried, homogenized soil sample underwent a QuEChERS extraction and dSPE clean-up. Calibration standards incorporated 45 native compounds and 14 13C-labeled internal standards across twelve levels. Quantitative analysis used full-scan electron ionization (EI) at 60,000 resolution, while unknown screening leveraged EI deconvolution and NIST library matching. Positive chemical ionization (PCI) confirmed molecular ions and adducts for suspect compounds.

Instrumentation

• Thermo Scientific Orbitrap Exploris GC with NeverVent technology
• ExtractaBrite EI and PCI ion sources
• Thermo Scientific TriPlus RSH autosampler
• TraceGOLD TG-5 SilMS capillary column
• Chromeleon 7.3 CDS and Compound Discoverer 3.2 software

Results and discussion

Chromatographic separation of critical PAH and PCB pairs was achieved in <20 minutes with baseline resolution. Method detection limits (MDLs) ranged from 118–475 fg on column (0.1–0.5 µg/kg), and limits of quantitation (LOQs) from 0.5–5 µg/kg. Calibration curves were linear (R2 ≥0.995) with residual factor %RSD <13%. Recoveries averaged 79% with extraction precision <5% RSD. Full-scan data enabled retrospective screening and identification of unexpected contaminants via deconvoluted EI and PCI confirmation.

Benefits and practical applications

The consolidated GC-Orbitrap workflow reduces solvent use, instrument downtime and labor compared to traditional Soxhlet or multi-method approaches. High resolution and accurate mass full-scan acquisition supports both targeted quantification and non-targeted screening in a single run, boosting throughput up to four-fold.

Future trends and possibilities of use

Advances in HRMS instrumentation, automated data processing and expanded spectral libraries will further streamline environmental contaminant analysis. Integration with in-line sample preparation and machine learning-driven compound identification could enable real-time monitoring and more comprehensive non-targeted workflows.

Conclusion

The combination of modified QuEChERS sample preparation, the Orbitrap Exploris GC platform and advanced data analysis delivers a robust, high-throughput solution for soil contaminant testing. The methodology provides sensitive, accurate quantification alongside reliable screening of unknowns, significantly improving laboratory productivity.

References

• CEN/TR 16998:2016 Ambient air – Report on nitro- and oxy-PAHs: origin, toxicity, concentrations and measurement methods.
• Sun et al., Environ. Int. 2017, 108, 261–270.
• Anderson & Achten, Polycyclic Aromatic Compounds 2015, 35, 330–354.
• Thermo Fisher Scientific, AN21736: Ultra-inert low bleed GC columns (2017).
• Hites, R.A., Environ. Sci. Technol. 2004, 38, 945.
• Stockholm Convention Guidance for PBDE Inventory (2018).
• Fernandes et al., Talanta 2004, 63, 1147–1155.