Why PFAS Measurement Matters for Regulation
Regulatory standards are only meaningful if contamination can be detected and quantified accurately. For PFAS—where MCLs are set at 4 parts per trillion (4 ng/L) for PFOA and PFOS—this requires analytical methods capable of detecting nanogram-per-liter concentrations in complex matrices including drinking water, groundwater, surface water, soil, sediment, blood serum, food, and air. The evolution of PFAS analytical chemistry over the past 25 years—from early immunoassay methods capable of detecting only at ppb levels to modern mass spectrometry achieving sub-ppt sensitivity—has been as important to regulatory progress as the policy development itself.
EPA Method 533 and Method 537.1: The Regulatory Foundation
EPA Method 537.1 (published 2018) and Method 533 (published 2019) are the primary EPA-validated analytical methods for measuring PFAS in drinking water. Method 537.1 covers 40 PFAS compounds using solid phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), achieving method detection limits (MDLs) of 0.1–3 ng/L depending on compound. Method 533 expands coverage to 25 additional short-chain PFAS (including PFBS, PFBA, and PFPeA) with MDLs as low as 0.5 ng/L. Together, these methods cover 65 PFAS compounds—the basis for compliance monitoring under the 2024 NPDWR. EPA’s Multi-Lab Validation study confirmed inter-laboratory reproducibility within 30% relative standard deviation for most compounds in both methods.
Non-Targeted Analysis: Seeing the Unknown PFAS
Traditional targeted methods measure only the specific compounds included in the method—missing the thousands of PFAS for which no standards exist. Non-targeted analysis (NTA) using high-resolution mass spectrometry (HRMS)—specifically Orbitrap and Q-TOF instruments—allows detection and tentative identification of unknown PFAS based on molecular formulas and fragmentation patterns. NTA studies regularly identify 5–20 times more PFAS compounds in environmental samples than targeted methods reveal. The National Environmental Methods Index (NEMI) and EPA’s CompTox Chemicals Dashboard support NTA data interpretation by providing mass spectral libraries and suspect screening lists. NTA is increasingly used in regulatory investigations to characterize the full PFAS burden at contaminated sites and in complex industrial waste streams.
Total Fluorine Methods: Combustion Ion Chromatography
Combustion ion chromatography (CIC) measures total organic fluorine (TOF) in a sample—providing a sum parameter that captures all organic fluorine regardless of compound identity. CIC is increasingly used for compliance monitoring in EU contexts (where the Drinking Water Directive uses a sum PFAS parameter) and for quality assurance of PFAS removal in treatment systems. The critical limitation: CIC cannot distinguish between different PFAS compounds or between PFAS and other organic fluorine sources (pharmaceuticals, fluorinated gases). Adsorbable organic fluorine (AOF) methods—similar to adsorbable organic halogen (AOX) methods—concentrate organofluorine on activated carbon before CIC analysis, improving sensitivity for aqueous samples. Several German states have used AOF as a regulatory compliance parameter for PFAS in surface water.
The TOP Assay: Measuring the Full PFAS Burden
The Total Oxidizable Precursor (TOP) assay, developed at Colorado State University, oxidizes all polyfluorinated precursor compounds to their terminal perfluorinated acid products using alkaline persulfate oxidation, then measures the increase in terminal PFAS concentration relative to an untreated sample. The difference between post-oxidation and pre-oxidation PFAS concentrations represents the “precursor pool”—PFAS precursors that would eventually transform to regulated compounds in the environment. TOP assay results at contaminated AFFF sites routinely show that terminal PFAS represent only 20–40% of total fluorinated compound burden, with precursors accounting for the remainder. EPA’s updated PFAS site investigation guidance recommends TOP assay as part of comprehensive site characterization. State cleanup programs in Michigan, Colorado, and New Jersey have incorporated TOP assay results into remediation planning.
Advances in PFAS analytical chemistry continuously expand what regulators and scientists can detect—meaning that regulatory frameworks based on today’s methods will need regular revision as analytical capabilities improve and more PFAS are brought into regulatory scope.