Preliminary Studies on the Recovery of SVOC from Soil using Pressurized Fluid Extraction with Methanol/Water

Importance of the Topic

This study addresses the extraction of semi-volatile organic compounds (SVOCs) from contaminated soils, a critical step in environmental monitoring and remediation. Traditional methods use large volumes of chlorinated solvents and lengthy evaporation steps, raising concerns about laboratory contamination, health risks, and processing time. Pressurized fluid extraction (PFE) with methanol/water and stir bar sorptive extraction offer a more sustainable approach.

Objectives and Overview of the Study

The work aimed to evaluate a combined PFE and PDMS-coated stir bar method for efficient recovery of SVOCs listed in EPA SW-846 Method 8270 from soil. The study used spiked Ottawa sand samples at 167 ppb levels and compared extraction efficiency, reproducibility, and detection limits.

Methodology

• Sample Preparation: Ottawa sand spiked with SVOC standard; extraction in ASE cells with 20 % methanol/water at 100 °C and 1500 psi.
• Stir Bar Extraction: Acidified extracts (pH ≤ 2) were subjected to overnight extraction with PDMS-coated stir bars (Gerstel Twister™).
• Analysis: Thermal desorption GC/MS (Agilent 6890/5973) with PTV inlet and splitless conditions for quantification.

Instrumentation

• Dionex Accelerated Solvent Extractor 200 (ASE 200)
• Gerstel Twister™ PDMS-coated stir bars
• Agilent Technologies GC/MS System (6890 GC and 5973 MSD)
• Gerstel Thermal Desorption Unit (TDS2/TDSA) and Programmable Temperature Vaporizing Inlet (CIS4 PTV)

Main Results and Discussion

• Recovery: Over 90 % of the lower boiling 40 SVOCs were extracted in the first ASE cycle; high-boiling PAHs required two cycles.
• Detection Limits: Mid-ppt (pg/g) range for most compounds was achievable using stir bar concentration.
• Reproducibility: RSD values of 10–30 % for the first extraction and improved precision when combining both extracts.
• Acidification improved recovery of phenolic compounds but limited some basic analytes.

Benefits and Practical Applications of the Method

The combined PFE and stir bar technique reduces use of toxic solvents, minimizes sample handling, and shortens overall analysis time. It enables high-sensitivity quantification of SVOCs in soil, supporting environmental assessments, remediation monitoring, and quality control in industrial settings.

Future Trends and Potential Applications

• Optimization of extraction parameters (temperature, solvent ratio, pH) for further improved recoveries.
• Application to a wider range of matrices, such as sediments and sludge.
• Integration with automated systems for high-throughput environmental monitoring.
• Exploration of alternative green solvents (ethanol, acetonitrile) in PFE processes.

Conclusion

The preliminary study demonstrates that pressurized fluid extraction with methanol/water coupled to PDMS-coated stir bar extraction is a viable, more sustainable alternative for SVOC analysis in soils. Further optimization promises enhanced sensitivity, reproducibility, and broader applicability in environmental chemistry.

References

1. Hawthorne S, Yang Y, Miller D. Extraction of Organic Pollutants from Environmental Solids with Sub- and Supercritical Water. Analytical Chemistry. 1994;66:2912-2920.
2. Yang Y, Bowadt S, Hawthorne S, Miller D. Subcritical Water Extraction of Polychlorinated Biphenyls from Soil and Sediment. Analytical Chemistry. 1995;67:4571-4576.
3. Pfannkoch E, Whitecavage J, Hoffmann A. Stir Bar Sorptive Extraction: Enhancing Selectivity of the PDMS Phase. Poster presented at Pittsburgh Conference; 2001; New Orleans, LA.
4. Dionex. Extraction of BNA (Bases, Neutrals, and Acids) Using Accelerated Solvent Extraction (ASE). Application Note 317; 2001.
5. Dionex. Extraction of PAHs from Environmental Samples by Accelerated Solvent Extraction (ASE). Application Note 313; 2001.