2019.06.10_CCO.p11_NCDEQTestAmericaTechnicalMemorandum

MEMORANDUM

Date: 6/7/2019

To: Dr. Lam Leung, Chemours
CC: Mike Aucoin, AECOM
From: Eric Redman, Director of Technical Services

Subject: LC/MS/MS Method Performance for DFSA

This technical memorandum addresses questions regarding observed variability in the
determination of DFSA (difluorosulfoacetic acid) by Eurofins TestAmerica’s current LC/MS/MS
methodology, known as the ‘Table 3+’ analytical method.

DFSA is a very small molecule by LC/MS/MS standards,
consisting of singe C1 fluorocarbon bonded to two acidic
moieties (carboxylic and sulfonic):

The size, structure, and highly polar nature of this molecule create a variety of technical challenges
for LC/MS analysis. Due to the size and structure of DFSA there are relatively few characteristic
mass fragments or mass transitions that can be used to identify DFSA in the LC/MS/MS
methodology, and the identification elements that exist are not unique to DFSA. DFSA is therefore
prone to a large range of chemical interferences that can adversely impact the performance of the
analytical method.

The small and highly polar nature of DFSA also means that it is not easily retained under the usual
LC/MS/MS chromatographic conditions. Poor retention in turn means that DFSA cannot be
chromatographically separated or resolved from physical or chemical interferences, and is therefore
more susceptible to adverse impacts from these co-eluting interferences. These can be manifest
as discreet interferences that mimic the MS/MS response of DFSA and either obscure its presence
(false negatives) or impart a positive bias (false positives). Additionally, non-discreet or bulk
interferences such as dissolved solids, high ionic content, and naturally occurring organic and ionic
compounds (humic acid or NOM) can create severe ion suppression and enhancement effects in
the LC/MS/MS analysis. DFSA is further prone to variable impacts from ionic substances (including
pH differences) due to its unusual di-acidic character.

The combination of multiple DFSA properties that can adversely impact analytical performance
means that current ‘Table 3+’ analytical procedures will generate variable and potentially unreliable
results for DFSA in samples. Analytical performance for DFSA has been demonstrated to be
reliable in the absence of matrix interferences, but a growing body of empirical evidence including
sample duplicate and matrix spike results indicates that matrix effects have a significant adverse
impact in field samples.