A Large Volume Injection Technique Using Simplified Sample Preparation for Perfluorinated Alkyl Substance (PFAS) in Soils in Accordance with ASTM 7968

Significance of the Topic

Perfluoroalkyl substances (PFAS) are persistent environmental pollutants that accumulate in soils from industrial discharges, consumer products, and firefighting foams. Their resistance to degradation and potential health impacts at trace levels make reliable soil analysis essential for monitoring, remediation, and risk assessment.

Objectives and Study Overview

This study evaluates a streamlined sample preparation and large-volume injection approach based on ASTM D7968 for quantifying 24 legacy and seven emerging PFAS in diverse soil matrices. The protocol aims to simplify laboratory workflows, improve throughput, and achieve detection in the low ng/kg (ppt) range using advanced LC-MS/MS instrumentation.

Methodology and Used Instrumentation

Soil samples (sand, silt, lean clay, fat clay) were spiked with PFAS standards, adjusted to pH 9–10, shaken, centrifuged, filtered, and acidified before analysis. A 30 µL injection of the extract underwent reversed-phase UPLC separation followed by electrospray MS/MS detection.

• ACQUITY UPLC I-Class PLUS System with PFAS Analysis Kit
• ACQUITY UPLC CSH Phenyl-Hexyl Column (2.1 × 100 mm, 1.7 µm)
• Waters Xevo TQ-XS Triple Quadrupole Mass Spectrometer
• MassLynx Software v4.2
• QuanOptimize and TargetLynx Application Managers

Main Results and Discussion

Required method blanks, LLOQ checks, and lab control samples met acceptance criteria. The lowest calibration point (5 ng/L in vial, corresponding to 25 ng/kg in soil) served as LLOQ for most analytes. Calculated detection limits were 5–10 times lower than ASTM D7968 calibration bounds. LLOQ recoveries ranged from 77 to 135%, within the 50–150% requirement. All compounds exhibited linear calibration (R² > 0.995). Recoveries of isotopically labeled surrogates in all soil types fell within the 70–130% range. Continuing calibration verifications over 90 injections across 36 hours demonstrated excellent signal stability and minimal matrix bias.

Benefits and Practical Applications

The simplified extraction coupled with large-volume injection reduces sample preparation time and consumables, increasing laboratory throughput. The method’s sensitivity and robustness support routine environmental monitoring, site assessments, and regulatory compliance for both regulated and emerging PFAS.

Future Trends and Opportunities

Advancements may include automation of the sample workflow, integration of additional PFAS and precursors, further reduction in sample volume or injection size, and enhanced measures for system cleanliness to mitigate background contamination. Expanded multi-class analyte panels could broaden environmental and human exposure studies.

Conclusion

The combination of simplified sample preparation, large-volume injection, and the Xevo TQ-XS platform effectively meets ASTM D7968 requirements for PFAS in soils. This approach offers a sensitive, accurate, and high-throughput solution for environmental laboratories.

References

• Organtini K.; Cleland G.; Rosnack K. Large Volume Direct Injection Method for PFAS in Water, ASTM 7979-17. Waters App. Note 720006329EN, 2018.
• Organtini K.; Rosnack K.; Stevens D.; Ross D. Analysis of Legacy and Emerging PFAS in Water by SPE and LC-MS/MS. Waters App. Note 720006471EN, 2019.
• Organtini K.; Brinster K.; Rosnack K. PFAS in Drinking Water: PS2 Cartridge Extraction, EPA 537.1. Waters App. Note 720006695EN, 2019.
• ASTM D7968. Determination of Polyfluorinated Compounds in Soil by LC-MS/MS. ASTM International, 2017.