A Novel Fluorine\nMass Balance Method for Improved\nCharacterization and Quantification of Extractable (Organo)fluorine\nin Drinking Water

Per- and polyfluoroalkyl substances (PFAS) are common\ncontaminants\nof drinking water globally. Due to their large number and diversity,\nextractable organofluorine (EOF) has been employed as a sum parameter\nmeasurement to capture known and unknown PFAS in environmental samples.\nHowever, current methods for determining drinking water EOF perform\npoorly for trifluoroacetic acid (TFA) and provide limited insights\ninto the nature of unidentified fluorine occurring in samples. To\naddress this, we developed and validated a solid-phase extraction\nprocedure for EOF determination in drinking water with improved TFA\nrecovery, which removes and/or accounts for different species of inorganic\nfluorine. The method produces two fractions: one containing mostly\npolar fluorinated substances (e.g., TFA, tetrafluoroborate, and trifluoromethanesulfonate)\nand another containing longer-chain PFAS. Hexafluorophosphate was\ndistributed across both fractions. Application of the method to Stockholm\ndrinking water revealed a closed fluorine mass balance in fraction\nI, predominantly (93%) consisting of TFA. In fraction II, however,\n67% of the fluorine was unidentified, pointing to unknown fluorinated\nsubstance(s) with similar physical–chemical properties to PFAS\nin this fraction (e.g., perfluorooctanesulfonate). In addition to\nproviding clues for identifying EOF, the method improves estimation\nof “PFAS Total” for comparison to limits under the European\nDrinking Water Directive.