Overview of the U.S. EPA Method 1633 for PFAS testing

Published May 15, 2024

Meeri Rantanen

Environment & Industry, Measurlabs

Finalized in January 2024, the U.S. Environmental Protection Agency’s (EPA) Method 1633 details the testing procedure for per- and polyfluoroalkyl substances (PFAS) in a variety of environmental matrices, including wastewater, surface water, groundwater, soil, sediment, and tissue samples.

The method is emerging as the go-to technique to analyze water for PFAS in the US, being recommended by the EPA to monitor contamination levels for National Pollutant Discharge Elimination System (NPDES) permits and Clean Water Act compliance.1

Compounds analyzed under Method 1633

PFAS are a group of thousands of synthetic organic compounds developed to repel water, dirt, and grease. They are often called “forever chemicals” because they degrade slowly and accumulate in nature.

Due to the abundance of substances, identifying and measuring the concentration of all PFAS compounds a sample contains is technically unfeasible. To get around this issue, Method 1633 lists 40 compounds that should be targeted. These have been chosen based on data from multi-laboratory validation studies, demonstrating that it is possible to analyze them reliably in all the relevant matrices.2

Table 1: PFAS compounds targeted under US EPA Method 1633

Compound

Abbreviation

CAS number

Perfluorobutanoic acid 

PFBA

375-22-4 

Perfluoropentanoic acid 

PFPeA

2706-90-3 

Perfluorohexanoic acid 

PFHxA 

307-24-4 

Perfluoroheptanoic acid 

PFHpA 

375-85-9

Perfluorooctanoic acid 

PFOA

335-67-1

Perfluorononanoic acid 

PFNA

375-95-1

Perfluorodecanoic acid 

PFDA

335-76-2 

Perfluoroundecanoic acid 

PFUnA 

2058-94-8

Perfluorododecanoic acid 

PFDoA 

307-55-1 

Perfluorotridecanoic acid 

PFTrDA

72629-94-8

Perfluorotetradecanoic acid 

PFTeDA 

376-06-7

Perfluorobutanesulfonic acid 

PFBS 

375-73-5

Perfluoropentanesulfonic acid 

PFPeS

2706-91-4

Perfluorohexanesulfonic acid 

PFHxS

355-46-4

Perfluoroheptanesulfonic acid 

PFHpS 

375-92-8 

Perfluorooctanesulfonic acid 

PFOS

1763-23-1

Perfluorononanesulfonic acid 

PFNS 

68259-12-1

Perfluorodecanesulfonic acid

PFDS 

335-77-3

Perfluorododecanesulfonic acid

PFDoS 

79780-39-5

1H,1H, 2H, 2H-Perfluorohexane sulfonic acid

4:2FTS

757124-72-4

1H,1H, 2H, 2H-Perfluorooctane sulfonic acid 

6:2FTS

27619-97-2

1H,1H, 2H, 2H-Perfluorodecane sulfonic acid 

8:2FTS 

39108-34-4

Perfluorooctanesulfonamide 

PFOSA 

754-91-6

N-methyl perfluorooctanesulfonamide 

NMeFOSA

31506-32-8

N-ethyl perfluorooctanesulfonamide 

NEtFOSA 

4151-50-2

N-methyl perfluorooctanesulfonamidoacetic acid 

NMeFOSAA 

2355-31-9 

N-ethyl perfluorooctanesulfonamidoacetic acid

NEtFOSAA

2991-50-6

N-methyl perfluorooctanesulfonamidoethanol 

NMeFOSE

24448-09-7

N-ethyl perfluorooctanesulfonamidoethanol 

NEtFOSE

1691-99-2

Hexafluoropropylene oxide dimer acid

HFPO-DA

13252-13-6 

4,8-Dioxa-3H-perfluorononanoic acid 

ADONA

919005-14-4

Perfluoro-3-methoxypropanoic acid 

PFMPA

377-73-1 

Perfluoro-4-methoxybutanoic acid 

PFMBA 

863090-89-5 

Nonafluoro-3,6-dioxaheptanoic acid 

NFDHA

151772-58-6

9-Chlorohexadecafluoro-3-oxanonane-1-sulfonic acid 

9Cl-PF3ONS

756426-58-1 

11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid

11Cl-PF3OUdS 

763051-92-9 

Perfluoro(2-ethoxyethane)sulfonic acid 

PFEESA 

113507-82-7

3-Perfluoropropyl propanoic acid 

3:3FTCA

356-02-5

2H,2H,3H,3H-Perfluorooctanoic acid

5:3FTCA

914637-49-3

3-Perfluoroheptyl propanoic acid 

7:3FTCA 

812-70-4

The substances targeted in the EPA 1633 Method give a representative picture of PFAS contamination, as they include a total of nine classes of compounds, as well as the most high-profile PFAS (PFOS, PFOA, PFNA, and PFHxS), which have been studied the most extensively and are globally regulated under the Stockholm Convention on Persistent Organic Pollutants.

Methodology: LC-MS/MS analysis

PFAS analysis by EPA 1633 is performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the multiple reaction monitoring (MRM) mode. Target compounds are quantified with respect to isotopically labeled standards.3 LC-MS/MS is a highly sensitive analysis technique capable of detecting trace quantities of analytes in different matrices, which makes it ideal for targeted PFAS analysis.

Sampling guidelines

The EPA 1633 method gives guidelines on sample collection, preservation, storage, and holding times to avoid cross-contamination and ensure representative sampling. All samples should be collected in PFAS-free-certified HDPE containers with linerless HDPE or polypropylene caps. Other recommendations include:

  • Composite sampling for Clean Water Act compliance monitoring is discouraged. Instead, samples should be collected from free-flowing sources like effluents or in-process waste streams.

  • The tendency of PFAS to be enriched in the surface layer of natural waters should be kept in mind for still water sampling. To test the overall PFAS content in the water body, the sample should be collected from below the surface. For a worst-case assessment, the sample should include the surface layer.

  • For previously unanalyzed aqueous sources, the nominal sample size is 500 mL. Generally, at least three aliquots of aqueous samples should be collected.

  • For leachate samples from landfills, three 100 mL aliquots should be collected.

  • For solids, such as soil, sediment, and biosolids, wide-mouth HDPE jars should be used. These should not be filled beyond three-quarters full.

  • For fish, field sampling protocols must be followed. If whole fish are collected, they must be wrapped in aluminum foil or inserted into food-grade polyethylene tubing.

The role of Method 1633 in PFAS analysis

Method 1633 plays an important part in the EPA’s efforts to manage PFAS pollution. Due to the meticulous development work, including multi-laboratory validation, the method enables reaching low detection limits in various environmental matrices. It also introduces clear guidelines to the still-emerging field of PFAS analysis, ensuring that contaminant level comparisons across projects are reliable. While it is not yet mandatory to follow the method when monitoring water quality for NPDES permits or Clean Water Act compliance, the EPA strongly recommends it. 

Measurlabs offers PFAS testing based on Method 1633 for surface, effluent, and groundwater. You can contact our experts through the form below to get a quote for your samples.

References:

1 Clean Water Act Analytical Methods, CWA Analytical Methods for Per- and Polyfluorinated Alkyl Substances (PFAS), EPA.

2 Section 1.6 of Method 1633 - Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS. Table 1 is adapted from Table 1 on page 49 of the Method.

3 Section 2 of Method 1633.

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