Quantification of Extractable Total Per- and Polyfluoroalkyl\nSubstances in Water Using Persulfate Preoxidation, Solid Phase Extraction,\nand Chemical Defluorination with Sodium Biphenyl or Ion-Pair Formation\nwith Methylene Blue

This research developed and optimized\ninnovative, cost-effective\nmethods to quantify extractable total per- and polyfluoroalkyl substances\n(PFAS) in water, overcoming limitations of existing techniques by\nintegrating persulfate preoxidation with subsequent solid phase extraction\n(SPE), followed by chemical defluorination using sodium biphenyl (SBP\nassay) or ion-pair formation with methylene blue (MB assay). Persulfate\npreoxidation improved selectivity by oxidizing interfering organofluorines\nand anionic surfactants, while SPE concentrated PFAS and removed impurities\nsuch as inorganic fluoride. Both the SBP and MB assays exhibited high\nresponses across various PFAS structures, except for some (ultra)short-chain\nPFAS. The refined assays, including SPE, achieved limits of detection\nof 0.016 μgF/L for SBP and 0.2 μgF/L for MB assay, with\nrobust recoveries across various PFAS compounds in synthetic water\nmatrices. Analyses of PFAS-contaminated real waters using the SBP\nassay revealed extractable total PFAS concentrations of 5.1 μgF/L\nin industrial wastewater and 0.30 μgF/L in river water, matching\nthose by combustion ion chromatography (CIC), a current benchmark\nmethod. The MB assay, however, showed concentrations 1.9–3.1\ntimes higher than the SBP and CIC assays. The extractable total PFAS\nconcentrations in the real waters exceeded the sum of individual PFAS\nquantified by LC–MS, underscoring the necessity of identifying\nunknown PFAS.