Oasis WAX for Extraction of Per- and Polyfluorinated Alkyl Substances (PFAS) from Drinking Water in Accordance with EPA Method 533

Importance of the Topic

Per- and polyfluorinated alkyl substances (PFAS) have emerged as critical water contaminants due to their persistence, bioaccumulation and potential health effects. Accurate monitoring of PFAS in drinking water at low levels is essential to comply with regulatory limits and ensure public safety.

Objectives and Study Overview

This study evaluates the Waters Oasis WAX cartridge as a solid phase extraction (SPE) tool for isolating 25 PFAS from drinking water in full conformance with EPA Method 533. The goal is to demonstrate that this cartridge matches the performance requirements for recovery, precision and detection set by the method, and to apply the complete workflow on a real sample to quantify PFAS levels.

Methodology and Instrumentation

• Sample Preparation and SPE
  Drinking water samples were collected and preserved according to EPA 533. Each 6 mL sample was passed through a 6 cc, 500 mg Oasis WAX cartridge (mixed-mode sorbent, pKa ~10) to capture PFAS.
• Instrumental Analysis
  Chromatographic separation and detection employed an ACQUITY UPLC I-Class PLUS System modified with the PFAS Kit, coupled to a Xevo TQ-S micro Tandem Quadrupole MS. A BEH C18 column (2.1 × 100 mm, 1.7 µm) was used at 35 °C with a water/methanol gradient containing ammonium acetate. The total run time was 22 minutes.

Main Results and Discussion

• Recovery and Accuracy
  Average recoveries for all 25 PFAS were within 80–100 % at 2 ng/L and 90–103 % at 12 ng/L, meeting the EPA requirement of 70–130 %.
• Precision
  Percent relative standard deviations (%RSD) were below 10 % for nearly all analytes, well within the 20 % threshold, except for 6:2 FTS which is prone to background contamination.
• Real-Sample Analysis
  In a triplicate analysis of a drinking water sample, nine PFAS were detected at concentrations between 0.48 and 5.28 ng/L. The summed PFAS concentration was 19.6 ng/L, below the EPA advisory level of 70 ng/L.

Benefits and Practical Applications

• Simplified Workflow
  The Oasis WAX cartridge integrates seamlessly with the EPA 533 protocol, reducing method development time.
• Regulatory Compliance
  High accuracy and precision support confident quantitation of PFAS at low ng/L levels in drinking water.
• Laboratory Efficiency
  Robust cartridge performance and a streamlined UPLC-MS setup enable high throughput and reliable data quality.

Future Trends and Opportunities

As regulations tighten and new PFAS emerge, mixed-mode SPE sorbents and enhanced MS workflows will play a central role in expanding analyte coverage and improving sensitivity. Integration with high-resolution mass spectrometry and automation could further increase throughput and data robustness for routine monitoring.

Conclusion

The Oasis WAX cartridge, in combination with the ACQUITY UPLC I-Class PLUS and Xevo TQ-S micro system, fulfills and surpasses the performance criteria of EPA Method 533. It provides a reliable and efficient solution for the extraction and quantitation of a broad suite of PFAS in drinking water.

References

• Waters Corporation Application Note 720006471EN, PFAS Analysis Method Conditions