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EPA Method 537.1 is the U.S. EPA-published analytical method for determining a defined list of per- and polyfluoroalkyl substances (PFAS) in drinking water by solid phase extraction and liquid chromatography/tandem mass spectrometry (LC-MS/MS). It is one of three EPA methods a lab, water utility, or environmental procurement officer is likely to encounter when scoping PFAS testing — alongside EPA Method 533 and EPA Method 1633 — and the three are not interchangeable. Which one applies depends on the regulatory driver (Safe Drinking Water Act monitoring versus Clean Water Act discharge monitoring), the sample matrix, and which PFAS compounds need to be quantified. This guide covers what Method 537.1 actually specifies, how it differs from Methods 533 and 1633, and what to evaluate when procuring PFAS testing capability — whether that means qualifying a contract laboratory or scoping in-house instrumentation.
What EPA Method 537.1 Covers
Method 537.1 (“Determination of Selected Per- and Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry”) is a revision of the original Method 537 published by EPA’s Office of Water. It specifies:
- Matrix: finished (treated) drinking water only — it is not validated for wastewater, groundwater, soil, biosolids, or tissue.
- Sample preparation: solid phase extraction (SPE) using 0.5 g, 6 mL styrene-divinylbenzene (SDVB) polymeric cartridges (§6.9.1) to concentrate PFAS analytes out of a 250 mL water sample. The method specifies that the sorbent “may not be modified with monomers other than SDVB”, and §1.6 forbids any change to the extraction steps in §11.4 — the reasoning behind fixing a sorbent and a water-only wash this tightly is set out in SPE cartridge selection and method optimization. (C18 does appear in the method, but as the LC column, not the extraction sorbent.)
- Detection: liquid chromatography/tandem mass spectrometry (LC-MS/MS), using isotope-dilution or labeled-analyte quantitation to correct for matrix effects and extraction losses.
- Analyte list: a defined set of PFAS compounds, including PFOA and PFOS, quantified against method-specific reporting limits.
Method 537.1 was developed for use under the Safe Drinking Water Act (SDWA), including EPA’s Unregulated Contaminant Monitoring Rule (UCMR) program, which requires public water systems to monitor for specific contaminants on a rotating schedule. A lab running Method 537.1 needs to demonstrate initial demonstration of capability (IDC), ongoing precision and recovery (OPR) checks, and method detection limit (MDL) studies consistent with the method’s quality-control requirements — this is the basis on which a procurement officer or utility should qualify a lab, not just a claim that the lab “runs 537.1.”
EPA Method 537.1 vs. Method 533 vs. Method 1633
These three methods are frequently confused because they all quantify PFAS by LC-MS/MS, but they cover different compound lists, different extraction chemistries, and — critically for procurement — different regulatory programs and sample matrices.
| Method | Matrix | Extraction | Typical use |
|---|---|---|---|
| EPA 537.1 | Finished drinking water only | SDVB solid phase extraction | SDWA compliance monitoring, UCMR |
| EPA 533 | Finished drinking water only | Isotope-dilution anion exchange SPE | SDWA compliance monitoring, UCMR; covers additional short-chain PFAS that 537.1 does not capture well |
| EPA 1633 | Wastewater, surface water, groundwater, soil, sediment, biosolids, landfill leachate, tissue | Isotope-dilution SPE (matrix-dependent) | Clean Water Act (NPDES) discharge monitoring, CERCLA/RCRA site investigation, multi-media PFAS characterization |
In practice, EPA has directed public water systems to run both Method 533 and Method 537.1 for UCMR 5 monitoring, because the two methods’ analyte lists and extraction chemistries are complementary — 533’s anion-exchange SPE recovers some shorter-chain PFAS that 537.1’s SDVB reversed-phase SPE does not capture as reliably, while 537.1 covers analytes not on the 533 list. Neither method is validated for anything other than finished drinking water, which is the single most common procurement mistake: specifying 537.1 or 533 for a wastewater, stormwater, or soil sample that actually requires Method 1633.
Method 1633 was finalized by EPA for use across a much wider set of matrices, developed jointly with the U.S. Department of Defense and Department of Agriculture, and is now the method EPA points to for PFAS monitoring under the Clean Water Act and for site investigation work outside the drinking-water program. If your testing need involves industrial discharge, groundwater at a contaminated site, biosolids, or fish tissue, Method 1633 — not 537.1 or 533 — is the applicable method.
What “PFAS Analysis Method” Means Beyond These Three
“PFAS analysis method” is sometimes used loosely to mean any of the above, but it also covers a broader family of EPA and non-EPA methods used for different sample types and regulatory contexts, including EPA Method 8327 (PFAS in non-potable water by LC-MS/MS, used for some state and RCRA programs) and ASTM/ISO methods used outside U.S. federal programs. When scoping a testing contract or RFP, specify the exact method number rather than “PFAS testing” generically — the method determines the analyte list, the achievable reporting limits, the applicable QA/QC requirements, and, ultimately, whether the resulting data is defensible for the regulatory purpose it’s collected for.
Procurement Checklist: Qualifying a Lab or Vendor for PFAS Testing
Because PFAS results are frequently used for regulatory compliance, litigation support, or public reporting, the data has to withstand scrutiny. When evaluating a contract laboratory, instrument vendor, or in-house build-out, verify the following on documented, checkable evidence rather than a sales claim:
- Accreditation scope. Confirm the lab holds current NELAP (National Environmental Laboratory Accreditation Program) accreditation, through a TNI (The NELAC Institute)-recognized accreditation body, specifically for the method and analyte list you need — accreditation is granted per method/matrix/analyte, not as a blanket certification. Ask for the current accreditation certificate and scope of accreditation, not a general statement of being “EPA certified” (a phrase with no formal regulatory meaning on its own).
- UCMR 5 laboratory approval, if applicable. Labs analyzing samples for UCMR 5 reporting must be on EPA’s approved laboratory list for the specific method. Verify current listing directly rather than relying on the lab’s own claim.
- DoD ELAP, if the work touches federal/military sites. The Department of Defense Environmental Laboratory Accreditation Program has its own PFAS-specific quality requirements that go beyond baseline NELAP accreditation for some project types.
- Reporting limits versus your compliance threshold. Confirm the lab’s validated reporting limits for each analyte are below whatever regulatory or advisory threshold you’re testing against — a lab that “can run the method” but reports at limits above your action level doesn’t solve your problem.
- Method-matrix fit. Confirm the specific method proposed is validated for your actual sample matrix (finished drinking water vs. wastewater/soil/tissue) — this is the single most common source of unusable data in PFAS procurement, per the method-scope distinctions above.
- Contamination control and field procedures. PFAS analysis is unusually sensitive to background contamination from sampling equipment, packaging, and even some PPE. A qualified lab or vendor should provide (and require you to follow) a documented field sampling protocol, including PFAS-free sample containers and field blank requirements — ask for this in writing before sampling, not after results come back with detects that can’t be distinguished from cross-contamination.
- Turnaround time and data package format. Confirm standard and rush turnaround times, and whether the lab provides a full data package (raw data, QC results, chain of custody) sufficient for regulatory submission or third-party review, not just a summary report.
In-House Capability vs. Contract Lab: What to Weigh
Standing up in-house LC-MS/MS capability for PFAS analysis is a substantial capital and staffing commitment — the instrumentation, clean-room sample prep space, and demonstrated method validation (IDC, MDL studies, ongoing QC) needed to produce defensible PFAS data are non-trivial even for labs that already run LC-MS/MS for other analytes, because PFAS work requires unusually strict contamination controls (PFAS-free labware, restrictions on Teflon-containing materials and certain PPE, dedicated prep space). For most water utilities, environmental consultancies, and site investigation programs, contracting to an accredited external lab remains the more common path unless PFAS testing volume is high and ongoing enough to justify the fixed cost of in-house capability. Either way, the accreditation and method-matrix-fit checks above apply the same way to an internal build-out’s validation plan as they do to a vendor RFP.
Frequently Asked Questions
What is EPA Method 537.1 used for?
It is used to quantify a defined list of PFAS compounds, including PFOA and PFOS, in finished drinking water, primarily for Safe Drinking Water Act compliance and monitoring programs such as UCMR.
What is EPA Method 1633?
EPA Method 1633 is a multi-matrix PFAS method covering wastewater, surface water, groundwater, soil, sediment, biosolids, and tissue, used mainly for Clean Water Act discharge monitoring and site investigation work — it is not a drinking-water compliance method under the SDWA.
What is EPA Method 533 and how is it different from 537.1?
Method 533 is also a drinking-water PFAS method, but it uses isotope-dilution anion exchange solid phase extraction rather than 537.1’s SDVB reversed-phase SPE, which allows it to recover some shorter-chain PFAS that 537.1 does not capture as reliably. EPA has directed water systems to run both methods together for UCMR 5 monitoring because their analyte lists are complementary.
What is a “PFAS analysis method” in general?
It’s a general term covering any validated analytical method — EPA Methods 537.1, 533, 1633, and 8327 among them — used to identify and quantify PFAS compounds in a given sample matrix. The applicable method depends on the matrix and the regulatory program the results will be used for.
Can one lab run all three methods (537.1, 533, and 1633)?
Many environmental labs are accredited for more than one, but accreditation is granted per method, matrix, and analyte list, not as a blanket PFAS capability — verify the lab’s specific accreditation scope covers the exact method and analyte list your project requires before contracting.
