Evaporative Losses of Perfluoroalkyl Sulfonamides during PFAS Analysis

Perfluoroalkyl sulfonamides (FASAs) have been detected in aqueous film-forming foams (AFFF), municipal wastewater, and consumer products, among others. Although the compounds can be quantified directly by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS-MS), methods that are frequently used to measure poly- and perfluoroalkyl substances (PFASs) for which standards are not available, like the total oxidizable precursor (TOP) assay, ¹⁹F-NMR and nontarget analysis often employ solid-phase extraction followed by elution in a polar organic solvent, such as methanol. Volatilization of FASAs during open blowdown of polar organic solvent extracts from soil, sediment, or aqueous samples leads to underestimation of PFAS concentrations. To assess the importance of this loss mechanism, we measured recovery of three FASAs under conditions relevant to environmental analysis. Recoveries of FASAs and other neutral PFAS, including FASAAs and FTCAs, from methanol during the nitrogen blowdown step decreased as analyte concentrations decreased, with recoveries of less than 1% at 2 μg/L (i.e., a concentration corresponding to about 4 ng/L in water samples prior to solid-phase extraction). The addition of 10 mM NaOH prior to the blowdown step improved recoveries to greater than 80% for all FASAs. NaOH addition prior to blowdown also resulted in an approximately 40% increase in the concentrations of precursors detected in diluted AFFF as measured with the total oxidizable precursor (TOP) assay. The increased concentrations could not be explained by analytes for which analytical standards were available. These findings highlight that volatilization during solvent evaporation can be a significant source of analytical bias for a broader class of neutral PFAS, with FASAs serving as an important example.