Utilization of Automated Solvent Extraction with a Triple Quadrupole Mass Spectrometer following EPA Method 1633 for PFAS Analysis in Soil

Importance of the Topic

Per- and polyfluoroalkyl substances (PFAS) are persistent chemicals of growing regulatory concern due to their environmental and health impacts. Traditional manual extraction methods for solid samples can be time-consuming and prone to variability. Automating solvent extraction and integrating it with sensitive LC-MS/MS detection addresses throughput, reproducibility, and detection limits required by modern environmental monitoring.

Study Objectives and Overview

This study evaluates an automated pressurized fluid extraction system coupled with a triple quadrupole mass spectrometer to analyze 40 PFAS compounds in soil according to EPA Method 1633. Key aims include assessing extraction efficiency, method detection limits, calibration performance, and applicability for routine laboratory use.

Methodology and Instrumentation

• Sample Preparation: 5 g Ottawa sand spiked with native PFAS and internal standards, loaded into 2-piece Q-Cup® cells with Q-Disc® filters.
• Automated Extraction: CEM EDGE PFAS Automated Extraction system using 0.05 M KOH in methanol, two extraction cycles and two wash cycles at 65 °C, total extraction time under 10 minutes per sample including automated rinse.
• Cleanup: Solid-phase extraction with Millipore-Sigma Carbopack and SupelClean ENVI-WAX sorbents following EPA 1633.
• Chromatography: Shimadzu LCMS-8060NX with a C18 analytical column (50×2.1 mm, 3 µm) and a C18 delay column to remove system PFAS background, gradient elution with 2 mM ammonium acetate in water and acetonitrile.
• Mass Spectrometry: Triple quadrupole MS in MRM mode; nebulizing gas 2 L/min, heating gas 15 L/min, drying gas 5 L/min, interface temperature 250 °C.
• Calibration and Verification: Calibration curve from 0.02 to 1.25 ng/mL with internal standards, verification every 10 injections, percent relative standard error (RSE) target ≤20%.

Results and Discussion

• Calibration Performance: RSE values below 18% for all 40 PFAS analytes; accuracy between 90% and 128% over the calibration range.
• Recovery: Spike recoveries ranged from 63% (PFDOS) to 115% (PFHxA), all within EPA Method 1633 acceptable criteria.
• Method Detection Limits: Achieved MDLs of 0.01–0.06 ng/L for perfluoroalkyl carboxylic and sulfonic acids, and 0.01–0.45 ng/L for other PFAS—approximately two-fold lower than those reported in EPA Method 1633.

Benefits and Practical Applications

• Significantly reduced hands-on time and improved consistency through automation.
• Enhanced sensitivity meeting or exceeding regulatory requirements for PFAS in soil.
• Scalable workflow suitable for environmental testing, QA/QC laboratories, and high-throughput research.

Future Trends and Opportunities

• Integration of automated extraction with high-resolution mass spectrometry for broader PFAS screening.
• Adaptation of the workflow to other complex matrices such as biosolids and tissue samples.
• Development of in-line cleanup modules and miniaturized extraction formats to further increase throughput.

Conclusion

The combination of the CEM EDGE PFAS Automated Extraction system with the Shimadzu LCMS-8060NX provides a validated, efficient, and highly sensitive method for PFAS analysis in soil, surpassing EPA Method 1633 performance metrics and offering a robust solution for environmental laboratories.

References

1. EPA Method 1633: Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS.
2. Appendix B to Part 136, Title 40—Definition and Procedure for the Determination of the Method Detection Limit—Revision 2.