NEMC: A consolidated approach for routine analysis of soil contaminants using GC-Orbitrap mass spectrometry

Importance of the Topic

Polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) are persistent environmental pollutants that resist degradation, bioaccumulate in food chains, and pose serious health risks even at trace concentrations. Monitoring these compounds in soils and other matrices is critical to protect human health and comply with regulatory limits. Traditional methods often involve lengthy extractions and multiple chromatographic runs per sample, limiting throughput and increasing costs. A consolidated, high-resolution mass spectrometry approach offers the potential to streamline workflows, improve sensitivity, and enable comprehensive screening of multiple contaminant classes in a single analysis.

Objectives and Overview

The study aimed to evaluate a unified method for quantifying a broad suite of soil contaminants—including sixteen EPA PAHs, seven marker PCBs, three oxy-PAHs, ten methyl-PAHs, and nine NSO-PAHs—using the Thermo Scientific™ Orbitrap Exploris™ GC system. Key goals included assessing quantitative performance, method robustness under routine injection loads, chromatographic separation efficiency within a 20-minute run time, and the capacity to screen additional unknown compounds in complex soil extracts.

Methodology and Instrumentation

Sample Preparation

• Soil samples were freeze-dried, homogenized, and sieved prior to extraction.
• A modified QuEChERS protocol was used for extraction and cleanup.
• Calibration employed twelve concentration levels of 45 native standards and 14 13C-labeled internal standards; matrix-matched spike levels ranged from 0.5 to 5.0 pg/µL.

Instrument Configuration

• Gas chromatograph: Thermo Scientific™ Trace 1310 GC with NeverVent™ technology for rapid column and source changes.
• Column: TraceGOLD™ TG-5 SilMS, 30 m ×0.25 mm i.d. ×0.25 µm film thickness.
• Autosampler: Thermo Scientific™ TriPlus™ RSH series.
• Mass spectrometer: Orbitrap Exploris GC with ExtractaBrite™ electron ionization source; switchable to positive chemical ionization (PCI) using ammonia in methane.
• GC run time: 20 min per injection; oven program from 40 °C to 350 °C with tailored ramps.
• MS settings: Full-scan 50–550 m/z (EI) or 65–690 m/z (PCI), resolving power 60,000 FWHM, scan speed 7.4 Hz.

Main Results and Discussion

Sensitivity and Linearity

• Method detection limits (MDLs) ranged from 115 to 475 fg on column (0.1–0.5 µg/kg in soil).
• Calibration was linear across 0.1–500 pg/µL (0.1–500 µg/kg) with R2 ≥0.995 and residuals below 13%.

Precision and Robustness

• Repeatability of peak areas for PAHs and PCBs remained under 20% RSD over 500 injections spanning three weeks.
• Switching between EI and PCI modes was achieved in under 2 minutes, enhancing flexibility for compound confirmation.

Chromatographic Performance

• Coeluting critical isomer pairs (e.g., benzo[a]anthracene/chrysene) were resolved with resolution factors ≥1.3 within a 20-min window.
• Complex extract TICs demonstrated clear separation and peak shapes for nitrogen-containing heterocycles and substituted PAHs.

Unknown Screening

• Compound Discoverer™ 3.2 software enabled deconvolution of EI spectra, NIST library matching, and identification of additional soil contaminants from full-scan data.
• PCI spectra provided molecular ion information for confirmation of unusual analytes (e.g., flutolanil adducts).

Benefits and Practical Applications

The consolidated GC-Orbitrap workflow significantly reduces sample handling, instrument time, and method complexity by combining multiple analyte classes into a single run. Femtogram-level sensitivity supports trace-level regulatory monitoring, while robust performance under high injection loads suits high-throughput environmental and QA/QC laboratories. Rapid source changeovers and integrated data processing accelerate turnaround and minimize instrument downtime.

Future Trends and Potential Applications

Further expansion of high-resolution GC-MS methods may include additional emerging contaminants such as halogenated transformation products or polar degradation compounds. Advances in software-driven deconvolution and machine learning-based spectral libraries will enhance unknown identification. Integration with automated sampling technologies and remote monitoring platforms could facilitate real-time environmental surveillance.

Conclusion

The consolidated Orbitrap Exploris GC approach delivers rapid, sensitive, and robust analysis of a wide range of soil pollutants in under 20 minutes per sample. By unifying PAH, PCB, and related analyte workflows and enabling unknown screening, this method streamlines laboratory operations and meets the demands of routine environmental monitoring.

Reference

No external literature list provided in the source document.