United States
Environmental Protection
Agency
Technical Advisory- Laboratory Analysis of
Drinking Water Samples for
Perfluorooctanoic Acid (PFOA) Using EPA
Method 537 Rev. 1.1
Office of Water (MS-140)
EPA 815-B-16-021
September 2016

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Address questions concerning this document to:
Dan Hautman, Deputy Director Technical Support Center
Standards and Risk Management Division
U.S. EPA, Office of Ground Water and Drinking Water
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
hautman.dan(5)epa.gov

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Scope
EPA has recently learned that laboratories have identified different approaches for implementation of
EPA Method 537 Rev 1.1 ("Method 537") for analysis of PFOA. Some laboratories have analyzed PFOA
by quantitation of only the linear isomer while others have quantified both linear and branched-chain
isomers to determine the concentration of PFOA. The linear isomer represents the predominant form of
PFOA, but samples may also have some degree of branched-chain isomers. Method 537 specifically
identifies PFOS, PFHxS, NetFOSAA and NMeFOSAA as containing branched isomers, and requires that
quantitative standards be used to correctly identify and quantitate all chromatographic peaks for these
chemicals. The method specifically addresses this for PFOS, PFHxS, NetFOSAA and NMeFOSAA because,
at the time the method was written, a quantitative standard that contained mixed (linear and branched)
isomers of these analytes was available (as it is today) and supported traditional quantitation of both
isomer types.
EPA is recommending that laboratories analyzing samples for PFOA using EPA Method 537 quantify both
linear and branched isomers in the future. Field sample measurement of PFOA may periodically show
multiple chromatographic peaks (representing a mix of isomers) that should be included in the
quantitation. EPA notes that the correct application of the method is to calibrate using a certified
quantitative standard that includes both the linear and branched isomers of each analyte, if available.
While, as of the release of this technical advisory, there is no certified quantitative mixed standard for
PFOA, the available PFOA standards can be used to account for mixed isomers. EPA is providing the
following Q&A to address the issue and provide clarifying information for laboratories, their customers,
and others.
How should laboratories quantitate PFOA using EPA Method 537?
To account for linear and branched isomers of PFOA, EPA recommends that integration and quantitation
of real-world drinking water samples include peaks that represent both linear and branched isomers.
Since there is currently no certified quantitative PFOA standard that contains both linear and branched
isomers that can be used to quantitate in the traditional manner, EPA recommends that until such
standard is available, labs use the following approach:
•	Calibrate instrumentation using a certified quantitative standard containing only the linear
isomer.
•	Identify the branched isomers by analyzing a "qualitative/semi-quantitative" PFOA mixed
standard that includes both linear and branched isomers (Wellington Laboratories. cat#:T-PFOA
or equivalent) and compare retention times and tandem mass spectrometry transitions.
•	Quantitate PFOA by integrating the total response (i.e., accounting for peaks that are identified
as linear and branched isomers) and relying on the initial calibration with the linear-isomer
quantitative standard.
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Will Method 537 require an addendum or revision?
EPA's Office of Research and Development expects to publish a method revision in the near future to
describe the recommended technique foraddressing mixed isomers in the absence of a quantitative
mixed standard. In the interim, EPA is posting this technical advisory to EPA's Drinking Water Analytical
Methods web page and PFAS web page and is advising laboratories currently running Method 537 to
follow the approach described above when measuring PFOA.
How should laboratories that have analyzed UCMR 3 drinking water
samples for PFOA using Method 537 address this advisory?
In considering this question EPA first undertook a reassessment of the PFOA results reported under the
Unregulated Contaminant Monitoring Rule (UCMR 3). EPA applied conservative assumptions to estimate
the potential contribution of branched isomers in samples, and has concluded that the impact on the
UCMR 3 PFOA data is very limited. Whereas EPA had previously identified that 63 of 4909 public water
systems [PWSs] (just under 1.3%) had one or more UCMR results with PFOA + PFOS above EPA's Health
Advisory value, the reassessment identified a total of 65 PWSs (just over 1.3%) that met the same
criteria. The factthat the reassessment had such little impact on the conclusions is to be expected since
less than 1% of the reported results for PFOA were at or above the minimum reporting level. Based on
the findings of EPA's re-assessment, the Agency has concluded that repeat UCMR sample collection and
analysis for PFOA is not warranted. EPA Regions will continue to work with their states to reach out to
any public water systems with reported or estimated PFOA + PFOS results above the Health Advisory
value.
What action should I take if I contracted with a commercial laboratory to
analyze my drinking water for PFOA?
If you contracted with a laboratory to analyze for PFOA in your drinking water and the combined
concentration of PFOA and PFOS was between 50 and 70 ppt, you might consider contacting the
laboratory to ensure that the analytical results reported by the laboratory are based on the more
comprehensive technique for measuring PFOA.
Are results for PFOS impacted by this issue?
No, as long as the laboratory has followed Method 537 as written. Certified quantitative PFOS
standards, containing both linear and branched isomers, are available today, as they were during UCMR
3 monitoring. Per Method 537, these mixed PFOS standards are to be used and quantitation is to include
PFOS peaks that are identified as linear and branched isomers. EPA is not aware of situations where
laboratories have been unable to procure the quantitative mixed PFOS standard for drinking water
analyses by Method 537 or have otherwise deviated from the method requirements for PFOS.
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