Pressurised Liquid Extraction of Polycyclic Aromatic Hydrocarbons from Soil and Sediment Samples

Significance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are common environmental contaminants with carcinogenic and mutagenic properties. Reliable, sensitive, and rapid analysis of PAHs in soils and sediments is essential for environmental monitoring, regulatory compliance, and risk assessment. Conventional extraction methods such as Soxhlet are laborious, consume large solvent volumes, and often require extensive cleanup. Pressurized Liquid Extraction (PLE) offers a faster, cleaner, and more automatable alternative that can be directly interfaced with chromatographic detection.

Objectives and Study Overview

This work aimed to miniaturize a PLE device for microgram-scale solid samples, integrate it at-line with large-volume injection (LVI) GC–MS, and optimize extraction parameters (solvent type, temperature, pressure, time) for the determination of EPA priority PAHs in soils and sediments. Performance was compared with conventional Soxhlet and liquid-partitioning methods.

Methodology

A stainless-steel extraction cell (10 mm × 3 mm I.D.) was packed with 50 mg of sample mixed with internal standard. A static–dynamic PLE protocol used 100 µL of toluene at 200 °C and 15 MPa for 10 minutes, followed by a brief dynamic purge. Extracts (50 µL) were transferred directly into a PTV-based LVI injector on GC–MS. Calibration employed internal (phenanthrene) and external (phenanthrene-d10) standards without additional cleanup.

Used Instrumentation

• Miniaturized PLE device with resistive heating and temperature control
• Phoenix 20 CU syringe pump for solvent delivery
• 6-port Valco valve for pressure regulation
• HP 6890 GC with Optic 2 PTV large-volume injector and Restek XTI-5 column
• HP 6890 Series MS detector in Selected Ion Monitoring mode

Main Results and Discussion

Optimal extraction conditions (100 µL toluene, 200 °C, 15 MPa, 10 min) yielded detection limits of 0.3–0.5 ng/mL for low–molecular-weight PAHs and 0.04–0.1 ng/mL for heavier congeners, corresponding to <9 ng/g in 50 mg samples. Method repeatability was better than 15% RSD. In organic and sandy soils and river sediment, PLE performance matched or exceeded Soxhlet extraction and outperformed liquid-partitioning, particularly for less volatile PAHs, without requiring post-extraction filtration.

Benefits and Practical Applications

The miniaturized PLE–LVI–GC–MS workflow drastically reduces solvent use (100 µL vs. tens of milliliters), sample mass (50 mg vs. hundreds of milligrams), and analysis time, while maintaining sensitivity and precision. Direct at-line coupling eliminates concentration and cleanup steps, increasing throughput and lowering operational costs. This makes it attractive for routine environmental monitoring, industrial QA/QC, and research laboratories.

Future Trends and Potential Applications

Future work may pursue further device miniaturization, full automation with robotic sample handling, and extension to other organic contaminants (pesticides, PCBs). Coupling with high-resolution MS or multidimensional chromatography could enable analysis of complex matrices. Field-deployable PLE–MS platforms may facilitate real-time environmental surveillance.

Conclusion

The presented miniaturized PLE coupled at-line with LVI–GC–MS provides an efficient, solvent-saving, and sensitive approach for PAH analysis in soils and sediments. It achieves low detection limits, high precision, and streamlined workflow, representing a significant advance over conventional extraction techniques.

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