Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Accordance With EPA 1633 Part 2: Analysis of Aqueous Matrices

Importance of the Topic

The increasing concerns over per- and polyfluoroalkyl substances (PFAS) in environmental waters have led to stringent regulatory requirements. Accurate and reliable analysis of PFAS is essential for monitoring compliance under the Clean Water Act and guiding remediation efforts. EPA Method 1633 provides a unified protocol for quantifying a broad suite of PFAS across various matrices, making it a critical tool for environmental laboratories and research institutions.

Objectives and Study Overview

This application note presents the second part of a series demonstrating a complete workflow for PFAS analysis in aqueous samples according to EPA 1633. The study aims to validate a streamlined sample preparation approach using a dual-phase SPE cartridge (Oasis WAX/GCB) and assess performance criteria on an ACQUITY Premier BSM FTN UPLC system coupled to a Xevo TQ Absolute Tandem Quadrupole MS. Authentic ground water, surface water, and municipal wastewater (influent and effluent) samples were evaluated.

Instrumentation

• Solid Phase Extraction: Oasis WAX/GCB bilayer SPE cartridges
• Liquid Chromatography: ACQUITY Premier BSM FTN UPLC system with Premier BEH C18 column and Atlantis Premier BEH C18 AX isolator column
• Mass Spectrometry: Xevo TQ Absolute in negative ESI mode
• Data Processing: waters_connect software for quantitation

Methodology and Sample Preparation

A 250 mL aliquot of each water sample was spiked with extracted and non-extracted internal standards, loaded onto the Oasis WAX/GCB cartridge, and eluted following modified EPA 1633 protocols. The dual-phase cartridge integrates graphitized carbon black for cleanup, eliminating dispersive steps. LC separation employed a gradient of ammonium acetate in water and acetonitrile at 0.3 mL/min, 35 °C column temperature, and 2 µL injection volume. MS parameters included 0.5 kV capillary voltage, 900 L/hr desolvation gas, and targeted MRM transitions for 40 PFAS analytes.

Main Results and Discussion

• Internal Standard Recovery: Mean recovery of extracted standards across 20 extracts was 91.2% with 9.2% RSD, meeting draft EPA 1633 acceptance criteria.
• Certified Reference Material: Analysis of Waters ERA PFAS in Wastewater CRM yielded average trueness of 92% (range 73–112%) for all targets.
• Authentic Samples: PFAS were detected in all matrices. Ground water contained 9 compounds (0.11–7.03 ng/L), surface water 12 compounds (0.17–15.4 ng/L), influent wastewater 19 compounds (up to 88.9 ng/L), and effluent wastewater 16 compounds, demonstrating effective removal of certain PFAS during treatment.
• Interference Resolution: LC method achieved baseline separation of cholic acid interferences from PFOS in wastewater samples.

Benefits and Practical Applications

• Reduced Sample Volume: 250 mL versus 500 mL lowers collection, shipment, and storage logistics.
• Streamlined Cleanup: Combined WAX/GCB SPE cartridge simplifies workflow and reduces contamination risk.
• Regulatory Compliance: Method performance fully aligns with EPA Method 1633 criteria, supporting environmental monitoring.
• Robust Quantitation: High precision and accuracy enable reliable PFAS screening in diverse water matrices.

Future Trends and Applications

• Expansion to Additional Matrices: Application to soils, biosolids, and tissue samples as EPA 1633 finalizes.
• Broadening Analyte Scope: Inclusion of emerging PFAS and novel transformation products.
• Automation and High Throughput: Integration of online SPE and robotics for larger sample sets.
• Advanced Screening Approaches: Coupling with high-resolution MS for non-targeted PFAS discovery.

Conclusion

The integrated workflow combining Oasis WAX/GCB SPE and LC-MS/MS on Waters instruments fulfills EPA 1633 requirements for aqueous samples. It delivers high recovery, accuracy, and processing efficiency while reducing preparation steps and sample volumes. This approach offers a practical solution for environmental laboratories tasked with comprehensive PFAS monitoring in water.

References

1. US EPA. Draft Method 1633: Analysis of PFAS in Aqueous, Solid, Biosolid, and Tissue Samples by LC-MS/MS, Draft 4, July 2023.
2. US EPA. CWA Analytical Methods for PFAS. Accessed November 17, 2023.
3. Organtini K., Rosnack K., Hancock P. Analysis of PFAS per EPA 1633 Part 1: Method Assessment. Waters Application Note 720008117, 2023.