Analysis of Per- and Polyfluoroalkyl Substances in Soil Extracts

Significance of the topic

Per and polyfluoroalkyl substances are persistent organofluorine compounds used in many industrial and consumer applications. Their strong adsorption to surfaces and low level occurrence in the environment create challenges for accurate trace analysis in soil extracts.

Goals and overview of the study

This application note presents a comprehensive workflow for sample preparation and LC/MS/MS analysis of 25 representative PFAS in soil. The study examines each step from extraction through filtration and instrumental detection to identify and mitigate sources of adsorption losses and background interferences.

Methodology and instrumentation

The procedures follow ASTM D7968 and EPA methods 8327 and 7979 using sandy loam spiked with targeted analytes and isotopically labeled surrogates. Key steps include: basification with ammonium hydroxide, extraction with methanol-water, centrifugation, filtration, acidification with acetic acid, and LC/MS/MS analysis. Calibration used external standards over 5 to 200 ng/L with 1/x weighting. Instrumentation

• Agilent 1290 Infinity II LC with ZORBAX RRHD Eclipse Plus C18 column at 30 °C
• Agilent InfinityLab PFC Delay Column
• Mobile phases of 20 mM ammonium acetate in water and 10 mM ammonium acetate in acetonitrile
• Agilent 6470 triple quadrupole LC/MS with Jet Stream ESI in negative mode
• 61 MRM transitions optimized for fragmentor and collision energies

Main results and discussion

Polypropylene centrifuge tubes and disposable syringes showed PFAS background levels below half the quantitation limit, confirming low contamination risk. Heating 50 mL polypropylene stock solution flasks to 50 °C with vortex mixing improved recoveries of long chain acids. Regenerated cellulose Captiva syringe filters provided low background and consistent recoveries without pre-rinsing. Matrix extracts revealed native PFAS levels in sandy loam and a pronounced ionization enhancement for 8:2 fluorotelomer sulfonate. Optimization of the ion source sheath gas temperature to 250 °C minimized thermal degradation of perfluoroalkyl carboxylic acids and stabilized precursor and neutral loss ion responses.

Benefits and practical applications

• Use of validated low-background consumables reduces contamination and adsorption losses
• Elimination of lengthy rinsing steps saves time, solvent, and waste disposal costs
• Controlled heating restores long chain analyte recoveries within method tolerances
• Comprehensive workflow supports regulatory compliance at low part-per-trillion levels

Future trends and possibilities

Development of novel inert materials and filter media may further streamline PFAS workflows. Integration of automated sample handling can improve throughput and reproducibility. Advances in field-ready sampling devices with PFAS-inert surfaces will enhance environmental monitoring accuracy. Expansion of targeted analyte lists and suspect screening approaches will broaden detection capabilities.

Conclusion

A systematic evaluation of consumables and method parameters yields a robust workflow for reliable quantitation of PFAS in soil extracts. Adoption of polypropylene tubes, disposable syringes, and regenerated cellulose filters without pre-rinsing combined with optimized LC/MS/MS conditions minimizes background, adsorption losses, and thermal degradation, enabling routine regulatory analysis.

References

• Prevedouros K Source Fate and Transport of Perfluorocarboxylates Environmental Science and Technology 2006 40 32 44
• Lath S Sorption of PFOA onto Different Laboratory Materials Filter Membranes and Centrifuge Tubes Chemosphere 2019 222 671 678
• Schaefer CE Uptake of Poly and Perfluoroalkyl Substances at the Air‐Water Interface Environmental Science and Technology 2019 53 12442 12448
• EPA SW-846 Method 8327 Per and Polyfluoroalkyl Substances Using External Standard Calibration and MRM LC/MS/MS US EPA 2019
• ASTM D7968 Standard Test Method for Determination of Polyfluorinated Compounds in Soil by LC/MS/MS ASTM International 2017
• ASTM D7979 Determination of Per and Polyfluoroalkyl Substances in Water, Sludge, and Wastewater by LC/MS/MS ASTM International 2019
• Sorengard M Losses of Poly and Perfluoroalkyl Substances to Syringe Filter Materials Journal of Chromatography A 2020 1609 460430
• Gao Y Simultaneous Determination of Legacy and Emerging PFAS in Fish by QuEChERS and UHPLC-MS Analytical Methods 2018 10 5715 5722
• Nakayama SF PFAS in Maternal Serum Method Development and Application Japan Environment and Children Journal of Chromatography A 2020 460933
• EPA PFAS Soil Validation Study responseepa gov site site_profile accessed May 2020