Extraction and analysis of poly- and perfluoroalkyl substances (PFAS) from soil

Significance of the Topic

Poly- and perfluoroalkyl substances (PFAS) are a class of highly persistent, bioaccumulative chemicals that pose growing environmental and health concerns. While historically monitored in water, recent evidence shows elevated PFAS levels in soils and sediments. Accurate, reliable extraction and quantification from solid matrices are essential for environmental monitoring, risk assessment, and remediation strategies.

Objectives and Overview of the Study

This study aimed to develop and validate a robust analytical workflow for simultaneous extraction and quantification of 24 PFAS—including C4–C14 perfluoroalkyl carboxylic acids, C4–C10 sulfonates, fluorotelomer sulfonates, and sulfonamides—from soil at levels between 1 and 400 ng/g. The new method was benchmarked against conventional sonication/vortex extraction to demonstrate improvements in recovery and accuracy.

Methodology and Instrumentation

A two-gram soil subsample was spiked with native and isotopically labeled PFAS standards and mixed with diatomaceous earth. An Accelerated Solvent Extractor (Thermo Scientific™ Dionex™ ASE™ 350) employing 80:20 methanol/acetonitrile at 100 °C, three static cycles, and 120 s purge time achieved 70–130 % target recovery. Extracts underwent solid-phase clean-up using a styrene-divinylbenzene SPE cartridge under vacuum. Final extracts were analyzed using a Thermo Scientific™ Vanquish™ UHPLC system coupled to a TSQ Quantis™ triple quadrupole mass spectrometer with H-ESI in negative mode. Key MS parameters included Q1/Q3 resolutions of 0.7 Da/1.2 Da and cycle time of 0.5 s. Chromatographic separation was achieved over a 15-minute gradient from 40 % to 90 % organic.

Main Results and Discussion

• Consistent recoveries (70–130 %) were obtained across all PFAS classes, outperforming manual extraction.
• Linearity was demonstrated from 1 to 400 ng/g with r2 ≥ 0.997 for all analytes; minor bias for PFTrDA was attributed to surrogate mismatch and isotopic interference.
• PFAS background in method blanks remained at or below 0.05 ng/g despite prior Teflon exposure in the ASE system.
• Analysis of an unspiked soil sample revealed native PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFHxS at 1–5 ng/g and PFOS at ~50 ng/g.

Benefits and Practical Applications

The optimized ASE approach offers rapid, high-throughput extraction of a broad PFAS spectrum from soils with minimal labor and solvent usage. It provides reliable quantification at sub‐ng/g levels for environmental monitoring programs and supports remediation efficacy assessment.

Future Trends and Opportunities

Emerging PFAS analogs and replacement chemistries will require expanded analyte panels and improved extraction selectivity. Integration of ultrahigh-resolution MS and automated sample preparation can further reduce detection limits and increase laboratory throughput. Miniaturized extraction platforms and field-deployable devices may enable in situ screening of contaminated sites.

Conclusion

An ASE-based workflow combined with SPE clean-up and LC-MS/MS detection provides a robust, sensitive, and accurate method for the extraction of diverse PFAS from soil. This approach overcomes limitations of traditional solvent agitation techniques and is suitable for routine environmental analysis.

Reference

MacLennan MS, Ng D, Hope D. Extraction of poly- and perfluorinated alkyl substances (PFAS) from solid matrices. SETAC North America 40th Annual Meeting; 2019.