LC-MS/MS analysis of per- and polyfluoroalkyl substances (PFAS) in soil samples in accordance with EPA Method 1633

Significance of the topic

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that pose health risks and accumulate in soil. Regulatory agencies worldwide, including the U.S. EPA, have established strict testing requirements to monitor PFAS levels in various matrices. Reliable, high-throughput soil analysis methods are essential to support environmental monitoring, remediation assessment, and compliance with evolving regulations.

Study objectives and overview

This work demonstrates the quantitation of 40 PFAS compounds in soil according to EPA Method 1633. The study integrates automated solid-phase extraction (SPE) cleanup using the Thermo Scientific Dionex AutoTrace 280 PFAS system, chromatographic separation with Vanquish Flex UHPLC, detection by TSQ Altis Plus triple quadrupole mass spectrometry, and data processing with Chromeleon CDS templates designed for EPA 1633 reporting.

Methodology and instrumentation

Sample preparation combined manual extraction and semi-automated SPE:

• Soil samples (5 g) fortified with PFAS standards and equilibrated with water.
• Three successive extractions with 0.3% ammonium hydroxide in water to maximize recoveries.
• Concentration under nitrogen to 10.5 mL, dilution to 40 mL (20% methanol), pH adjustment to 6–7.
• Automated cleanup on GCB/WAX SPE cartridges via the AutoTrace 280 PFAS instrument using conditioning (1% methanolic NH₄OH, 0.3 M formic acid), sample loading, rinses, drying, and elution steps.
• Addition of internal standards, acidification, filtration through pre-rinsed 0.2 µm nylon syringe filters, and transfer to 1.5 mL autosampler vials.

Chromatography used a Hypersil GOLD delay column (4.6 × 50 mm, 1.9 µm) and Acclaim 120 C18 analytical column (2.1 × 50 mm, 2.2 µm) with a water/acetonitrile gradient containing ammonium acetate and acetic acid at 0.4 mL/min and 40 °C. Injection volume was 5 µL.
Mass spectrometry employed the TSQ Altis Plus in timed SRM mode, with compound-specific transitions, optimized collision energies, and RF lens settings. Nine calibration levels (1/x weighting, quadratic fits for selected analytes) ensured accurate quantitation.
Data acquisition and reporting used Chromeleon CDS templates configured for EPA Method 1633, including surrogate recovery, MDL calculation, and QC metrics.

Main results and discussion

Method detection limits (MDLs) for all 40 PFAS ranged from 0.007 to 0.116 ng/g with accuracy within ±20% of target values; 18 compounds showed accuracy within ±10%. Calibration curves exhibited relative standard errors below 10% for most analytes and remained under 20% for all targets. Surrogate and internal standard recoveries met EPA Method 1633 acceptance criteria, demonstrating the robustness of the automated SPE cleanup. The integrated workflow minimized background contamination in method blanks and delivered consistent precision across replicate analyses.

Benefits and practical applications

• Comprehensive vendor-supplied workflow reduces method development time and risk of contamination.
• Automated SPE cleanup improves laboratory throughput and minimizes manual errors compared to vacuum manifolds.
• High sensitivity of the TSQ Altis Plus allows low-level detection of PFAS in complex soil matrices.
• Chromeleon CDS templates streamline compliance with EPA reporting requirements, supporting environmental laboratories and QA/QC operations.

Future trends and opportunities

Emerging PFAS of interest and expanded compound lists will drive further method refinement. Advances may include higher-capacity SPE cartridges, deeper automation, and coupling with high-resolution mass spectrometry for non-targeted PFAS screening. Integration with laboratory information management systems (LIMS) and cloud-based data analytics will enhance data accessibility and regulatory reporting efficiency.

Conclusion

The presented workflow demonstrates accurate, precise quantitation of 40 PFAS in soil following EPA Method 1633. Automated SPE cleanup on the AutoTrace 280 PFAS instrument combined with Vanquish Flex UHPLC and TSQ Altis Plus MS delivers reliable low-level detection, high throughput, and regulatory compliance in environmental PFAS monitoring.

References

• U.S. EPA. Method 1633: Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS. January 2024.
• Thermo Fisher Scientific. Application Note 002348: Quantitation of per- and polyfluoroalkyl substances (PFAS) in aqueous samples by LC-MS/MS following EPA Draft Method 1633.