Pushing PFAS Possibilities: The Hunt For Ultra Sensitivity To Reach PPQ EPA Health Advisory Levels

Importance of the Topic

Per- and polyfluoroalkyl substances (PFAS) are persistent pollutants with growing regulatory scrutiny due to their health risks at ultra-trace levels. Recent US EPA health advisory levels (HALs) for PFOA and PFOS in drinking water have been tightened from 70 ng/L to sub-ppt concentrations (0.004 and 0.02 ng/L respectively). Achieving reliable detection at these limits is critical for environmental monitoring, public health protection, and regulatory compliance.

Objectives and Study Overview

This study aimed to develop and validate an ultra-sensitive workflow for quantifying four regulated PFAS (PFOA, PFOS, PFBS, and GenX) at or below the new EPA HALs. Key goals included optimization of sample enrichment, chromatographic separation, mass spectrometric sensitivity, and contamination control. The performance was evaluated across two independent laboratories to demonstrate method robustness and reproducibility.

Methodology and Used Instrumentation

Water samples were pre-concentrated 500-fold using Oasis WAX solid-phase extraction (SPE) cartridges under stringent clean-lab conditions to minimize artifact introduction. Chromatographic analysis was performed on a UPLC system equipped with a PFAS-optimized kit and a Premier BEH C18 column (2.1 x 100 mm, 1.7 μm). Mobile phases consisted of water and methanol, each containing 2 mM ammonium acetate, with a gradient from 95:5 to 5:95 (A:B). Detection employed a triple quadrupole mass spectrometer in negative electrospray ionization using enhanced sensitivity settings.

• UPLC System: ACQUITY Premier UPLC with PFAS Analysis Kit
• Column: ACQUITY Premier BEH C18, 2.1 x 100 mm, 1.7 μm
• MS: Xevo TQ Absolute with ESI source
• Software: waters_connect for Quantitation
• SPE: Oasis WAX Cartridges

Main Results and Discussion

Calibration curves for PFOA, PFOS, PFBS, and GenX were linear from 0.0005 to 0.08 ng/L (0.25–40 ng/L in vial equivalent) with correlation coefficients ≥ 0.992. Limits of quantitation (LOQs) for all compounds were well below interim and final EPA HALs in both laboratories, with signal-to-noise ratios ≥ 10.

Blank analyses confirmed absence of PFAS contamination in the LC-MS/MS system and sample vials. Extraction blanks showed minor PFOA and PFOS carry-over but remained below one-third of the minimum reporting level stipulated by EPA methods. Spike recovery experiments at 0.004 and 0.02 ng/L demonstrated recoveries between 90 and 111% and relative standard deviations (RSD) of 2–13%, indicating excellent accuracy and precision for trace-level quantitation.

Benefits and Practical Applications

• The combined SPE-UPLC-MS/MS workflow reliably meets or exceeds EPA HAL requirements in routine laboratory settings.
• High enrichment factor and sensitive detection ensure confidence in reporting ultra-low PFAS concentrations.
• Method robustness across two geographically distinct labs demonstrates reproducibility for regulatory monitoring and quality assurance.
• Standard laboratory equipment and SPE materials suffice, avoiding need for specialized infrastructure.

Future Trends and Potential Applications

Anticipated advancements include automation of SPE workflows to reduce manual handling and contamination risk. Emerging high-resolution mass spectrometers and novel ionization sources may further lower detection limits. Integration of data analytics and machine learning for peak deconvolution can streamline quantitation across broader PFAS panels. On-site or field-deployable systems could enable rapid screening in environmental emergencies or remote communities.

Conclusion

The presented workflow combining Oasis WAX SPE cartridges with UPLC-MS/MS on a Xevo TQ Absolute instrument achieves ultra-trace PFAS quantitation at sub-ppt levels required by new EPA guidelines. Method validation across two labs confirms its suitability for consistent, accurate, and precise monitoring of drinking water, supporting regulatory compliance and public health protection.

Reference

Organtini K, Fujimoto G, Foddy H, Dreolin N, Adams S, Rosnack K, Meruva N, Hancock P. Pushing PFAS Possibilities: The Hunt for Ultra Sensitivity to Reach PPQ EPA Health Advisory Levels. Waters Corporation, Application Note, 2023.