2020.10.02_CCO_DEQIsomerResponseLetter

October 2, 2020

Ms. Christel Compton
The Chemours Company FC, LLC
22828 Hwy 87 W
Fayetteville, NC 28306

Re: Isomer Response

Dear Ms. Compton,

In response to the August 26, 2020 letter, the July 17, 2020 Isomer Report, and the
technical call on September 22, 2020, DEQ recommends additional LC/MS/MS experiments
be performed prior to running environmental samples. The purpose of these experiments
is to definitively show not only which isomers are present in the standards and samples but
also to confirm if other isomers are present, even at low levels, or if they are entirely
absent.

The July 17, 2020 report does not provide sufficient analytical assessment of the linear
isomers (PFMOPrA and PFMOBA). While the report does show that the dominant species
present are likely to be the branched isomers (PMPA and PEPA), additional work should be
conducted to show whether or not the linear isomers are also present in the analytical
standards and environmental samples. The LC/MS/MS experiments performed should be
repeated with method improvements that allow for better chromatographic separation and
instrument detection of the four individual analytes of interest.

Method improvements are recommended for this investigation only. Routine analysis of
the isomers would not require implementation of all suggested method changes for the
isomer evaluation. However, some of the method changes may help with future routine
analysis. Chemours’ August 26, 2020 letter states an intention to analyze a set of samples
to establish if there are any false positives. It is recommended that further method
development be conducted prior to analyzing these samples so it is clear that the linear
isomers are sufficiently assessed by these methods. Recommended method improvements
are listed below. More detailed information, including a proposed path forward, is
described in the attached supporting information. In summary:

1) Use four separate solutions for the four analytical standards rather than
mixtures.
2) Use sufficient concentrations of standards for strong peaks (minimum
instrument response of 106) to determine any impurities in each of the four
standards.
3) Optimize the mass spectrometer settings for the linear isomers when analyzing
for them.
4) Chromatographically resolve (separate) each isomer pair, and monitor multiple
MRM transitions for each peak to determine individual isomer
presence/absence.

Review Certificates of Analysis from Wellington and publications by Strynar et al. 2015 and
Song et al. 2018 for examples of LC/MS/MS methods for analysis of these isomers. Once
these methods are demonstrated for characterizing the 4 analytical standards, the
optimized methods for each compound should be applied to investigating the potential
presence of linear isomers in the environmental samples using linear calibration standards.

Please let us know of any questions.

Sincerely,

Michael E. Scott
Director, Division of Waste Management
NC DEQ