A Consolidated Approach for Routine Analysis of Soil Contaminants using GC-Orbitrap Mass Spectrometry

Significance of the Topic

Polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) are harmful, persistent organic pollutants that accumulate in soil and the food chain, posing significant human health risks even at trace levels. High-throughput, sensitive methods are needed to meet regulatory requirements and streamline environmental monitoring.

Objectives and Study Overview

This study aimed to develop a consolidated analytical workflow using a Thermo Scientific Orbitrap Exploris GC system to quantify sixteen EPA PAHs, seven marker PCBs, and various substituted PAH derivatives in soil. Key goals included achieving femtogram-level sensitivity, rapid throughput, and robust performance across hundreds of samples in a single chromatographic method.

Methodology and Instrumentation

A modified QuEChERS extraction was applied to freeze-dried, homogenized soil, spiked with surrogate standards. Separation was performed on a 30 m × 0.25 mm TG-5 SilMS column using a 20 min temperature program. Detection employed an Orbitrap Exploris GC with ExtractaBrite™ electron ionization and positive chemical ionization options, full-scan acquisition (m/z 50-550) at 60,000 resolution. NeverVent™ technology enabled <2 min source and column changes. Data were processed in Chromeleon™ 7.3, and Compound Discoverer™ 3.2 facilitated deconvolution and library matching.

Key Results and Discussion

• Method detection limits ranged from 115 to 475 fg on column (0.1–0.5 μg/kg in soil).
• Calibration was linear over 0.1–500 pg/μL with R² ≥0.995 and residuals <13%.
• Repeatability across 500 QuEChERS injections showed peak area RSDs <20%, averaging ~10.5% over three weeks.
• Chromatographic separation resolved critical isomers (<20 min), achieving symmetry factors near 1.0 and resolution >1.0 for key PAH and PCB pairs.
• Rapid switch from EI to PCI allowed confirmation of molecular ions and improved identification confidence.

Benefits and Practical Applications

• Consolidates multiple analyte classes into a single 20 min run, reducing labor, solvent use, and instrument time.
• Femtogram sensitivity meets stringent regulatory limits, enabling trace-level monitoring in environmental and QA/QC labs.
• High throughput with minimal downtime supports routine large-scale soil screening programs.
• Software-driven deconvolution and library searches accelerate unknown screening and data review.

Future Trends and Potential Applications

• Extension to emerging soil contaminants such as halogenated flame retardants and per- and polyfluoroalkyl substances.
• Integration of suspect and non-target screening workflows powered by high-resolution data and AI algorithms.
• Automation of sample preparation and data processing to further increase laboratory efficiency.
• Miniaturization of extraction methods and field-deployable high-resolution instruments for in situ analysis.

Conclusion

The consolidated GC-Orbitrap approach demonstrated robust sensitivity, linearity, and repeatability for a broad range of PAHs, PCBs, and substituted derivatives in soil within a single method. Implementation of rapid vent-free maintenance and software-driven data analysis streamlines environmental monitoring and supports high-throughput laboratory demands.

Used Instrumentation

• Thermo Scientific™ Orbitrap Exploris GC with NeverVent™ technology.
• ExtractaBrite™ electron ionization and PCI sources.
• Thermo Scientific™ TriPlus™ RSH autosampler.
• TraceGOLD™ TG-5 SilMS 30 m × 0.25 mm × 0.25 μm capillary column.
• Thermo Scientific™ Chromeleon™ 7.3 and Compound Discoverer™ 3.2 software.