Determination of Selected Polychlorinated Biphenyls in Soil Using a QuEChERS-based Method and Gas Chromatography Tandem Mass Spectrometry

Significance of the Topic

Soils act as primary reservoirs for polychlorinated biphenyls (PCBs) due to their persistence, hydrophobicity, and potential for long-range transport. Reliable and sensitive soil analysis methods are essential for pollution assessment, environmental monitoring, and risk evaluation of these toxic compounds.

Objectives and Study Overview

This study aimed to develop a streamlined, QuEChERS-based extraction procedure combined with gas chromatography-tandem mass spectrometry (GC-MS/MS) to quantify 20 selected PCB congeners in agricultural soils. Key goals included minimizing solvent use, reducing analysis time, and achieving low limits of quantitation (LOQs) with robust recovery and precision.

Methodology

Sample preparation employed a modified QuEChERS workflow:

• Hydration of 5 g soil with water and ceramic homogenizer
• Extraction with acetonitrile, addition of NaCl, vortex mixing, and centrifugation
• Dispersive SPE cleanup using PSA, C18, and MgSO₄ adsorbents
• Evaporation under nitrogen and reconstitution in cyclohexane

Instrumentation Used

The clean extracts were analyzed on a GC-MS/MS system:

• Gas chromatograph: Agilent 7890A with 7693 autosampler
• Column: Agilent HP-5 MS UI (30 m × 0.25 mm, 0.25 μm film)
• Carrier gas: Helium at 1.0 mL/min
• Oven program: 60 °C (1 min), ramp to 120 °C at 40 °C/min, then to 275 °C at 5 °C/min
• Mass spectrometer: Agilent 7000C Triple Quadrupole, EI source (70 eV), MRM acquisition

Key Results and Discussion

Method validation showed:

• Recoveries between 70 % and 120 % across spiking levels (0.1, 1, 10 ng/g)
• Relative standard deviations (RSDs) mostly below 10 %
• LOQs in the range 0.01–0.05 ng/g
• Calibration curves linear with R² > 0.999

Analysis of a certified reference material and 66 agricultural soil samples confirmed method accuracy and applicability. Nine PCB congeners were detected at low levels in field soils, demonstrating environmental relevance.

Benefits and Practical Applications

• Significant reduction in solvent consumption (10 mL acetonitrile per sample)
• Short extraction time (3 min vortex) and minimal equipment requirements
• High sensitivity and precision suitable for routine monitoring
• Environmentally friendly and cost-effective approach for QA/QC laboratories

Future Trends and Potential Applications

Emerging directions include:

• Adaptation of QuEChERS for other persistent organic pollutants and complex matrices
• Integration with automated, high-throughput workflows and miniaturized extraction devices
• Advances in green chemistry to further reduce solvent use and waste
• Deployment of portable GC-MS systems for on-site soil screening
• Application of data analytics and machine learning for rapid spectral interpretation

Conclusion

The presented QuEChERS-GC-MS/MS method offers a rapid, sensitive, and robust solution for the determination of selected PCBs in soil. Its simplicity, low solvent usage, and strong validation performance support its adoption for environmental behavior studies and routine contamination monitoring.

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