Section 141.901 - Analytical requirements(a)General.(1) Systems must use only the analytical methods specified in this section to demonstrate compliance with the requirements of this subpart.(2) The following documents are incorporated by reference with the approval of the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51 . This material is available for inspection at the EPA and at the National Archives and Records Administration (NARA). Contact the EPA's Drinking Water Docket at: 1301 Constitution Avenue NW., EPA West, Room 3334, Washington, DC 20460; phone: 202-566-2426. For information on the availability of this material at NARA, email: fr.inspection@nara.gov, or go to: www.archives.gov/federal-register/cfr/ibr-locations. The material may be obtained from the EPA at 1301 Constitution Avenue NW, the EPA West, Room 3334, Washington, DC 20460; phone: 202-566-2426; website: https://www.epa.gov/pfas/epa-pfas-drinking-water-laboratory-methods. (i) EPA Method 533: Determination of Per- and Polyfluoroalkyl Substances in Drinking Water by Isotope Dilution Anion Exchange Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry, 815-B-19-020, November 2019.(ii) Method 537.1, Version 2.0: Determination of Selected Per- and Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS), EPA/600/R-20/006, March 2020.(b)PFAS -(1)Analytical methods. Systems must measure regulated PFAS by the methods listed in the following table: Table 1 to Paragraph (b)(1)-Analytical Methods for PFAS Contaminants
| Contaminant | Methodology | EPA method (incorporated by reference, see paragraph (a) of this section) |
| Perfluorobutane Sulfonate (PFBS) | SPE LC-MS/MS | 533, 537.1, version 2.0. |
| Perfluorohexane Sulfonate (PFHxS) | SPE LC-MS/MS | 533, 537.1, version 2.0. |
| Perfluorononanoate (PFNA) | SPE LC-MS/MS | 533, 537.1, version 2.0. |
| Perfluorooctanesulfonic Acid (PFOS) | SPE LC-MS/MS | 533, 537.1, version 2.0. |
| Perfluorooctanoic Acid (PFOA) | SPE LC-MS/MS | 533, 537.1, version 2.0. |
| 2,3,3,3-Tetrafluoro-2-(heptafluoropropoxy)propanoate (HFPO-DA or GenX Chemicals) | SPE LC-MS/MS | 533, 537.1, version 2.0. |
(2)Laboratory certification. Analyses under this section for regulated PFAS must only be conducted by laboratories that have been certified by EPA or the State. To receive certification to conduct analyses for the regulated PFAS, the laboratory must:(i) Analyze Performance Evaluation (PE) samples that are acceptable to the State at least once during each consecutive 12-month period by each method for which the laboratory desires certification.(ii) Beginning June 25, 2024, achieve quantitative results on the PE sample analyses that are within the following acceptance limits: Table 2 to Paragraph (b)(2)(ii) -Acceptance Limits for PFAS Performance Evaluation Samples
| Contaminant | Acceptance limits (percent of true value) |
| Perfluorobutane Sulfonate (PFBS) | 70-130 |
| Perfluorohexane Sulfonate (PFHxS) | 70-130 |
| Perfluorononanoate (PFNA) | 70-130 |
| Perfluorooctanesulfonic Acid (PFOS) | 70-130 |
| Perfluorooctanoic Acid (PFOA) | 70-130 |
| 2,3,3,3-Tetrafluoro-2-(heptafluoropropoxy)propanoate (HFPO-DA or GenX Chemicals) | 70-130 |
(iii) For all samples analyzed for regulated PFAS in compliance with § 141.902 , beginning June 25, 2024, report data for concentrations as low as the trigger levels as defined in § 141.902(a)(5) .