Why New Methods Were Needed
EPA Method 537.1, the first widely used PFAS drinking water analytical method, targeted a list of specific PFAS compounds but missed many emerging short-chain and newer PFAS variants. As the regulatory focus expanded from PFOA and PFOS to a broader range of PFAS including GenX and PFBS, Method 537.1’s compound coverage became insufficient. EPA Method 533, published in 2019, was designed specifically to address short-chain PFAS and expand the detectable compound list, enabling testing relevant to EPA’s current regulatory compound coverage.
Method 533 Technical Overview
EPA Method 533 uses isotope dilution liquid chromatography tandem mass spectrometry (LC-MS/MS) to quantify 25 PFAS compounds in drinking water, including several short-chain compounds not addressed by Method 537.1. The method uses mixed-mode anion exchange solid phase extraction for sample preparation, which improves recovery of short-chain PFAS compared to previous reversed-phase extraction approaches. Method detection limits for most target compounds are below 1 part per trillion, providing adequate sensitivity for compliance monitoring against the 4 ppt PFOA and PFOS MCLs.
Certified Laboratory Requirements
Laboratories performing EPA Method 533 for drinking water compliance monitoring must be certified by their state drinking water program and demonstrate analytical performance meeting method quality control criteria. Proficiency testing programs verify laboratory capability to accurately measure PFAS at low concentrations. When selecting a laboratory for PFAS testing, confirming Method 533 certification (rather than Method 537.1 only) ensures coverage of the short-chain PFAS compounds now regulated under the 2024 MCL rule.
Limitations and Emerging Methods
Neither Method 533 nor 537.1 covers all PFAS compounds in environmental waters. Suspect screening and non-targeted analysis methods using high-resolution mass spectrometry can detect thousands of PFAS compounds not included in target methods, providing a more complete picture of PFAS occurrence but requiring more sophisticated analytical infrastructure and data interpretation. These broader screening approaches are increasingly used in research and site investigation contexts to identify the full PFAS signature of contaminated water sources before treatment system design.