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

This research developed and optimized innovative, cost-effective methods to quantify extractable total per- and polyfluoroalkyl substances (PFAS) in water, overcoming limitations of existing techniques by integrating persulfate preoxidation with subsequent solid phase extraction (SPE), followed by chemical defluorination using sodium biphenyl (SBP assay) or ion-pair formation with methylene blue (MB assay). Persulfate preoxidation improved selectivity by oxidizing interfering organofluorines and anionic surfactants, while SPE concentrated PFAS and removed impurities such as inorganic fluoride. Both the SBP and MB assays exhibited high responses across various PFAS structures, except for some (ultra)short-chain PFAS. The refined assays, including SPE, achieved limits of detection of 0.016 μgF/L for SBP and 0.2 μgF/L for MB assay, with robust recoveries across various PFAS compounds in synthetic water matrices. Analyses of PFAS-contaminated real waters using the SBP assay revealed extractable total PFAS concentrations of 5.1 μgF/L in industrial wastewater and 0.30 μgF/L in river water, matching those by combustion ion chromatography (CIC), a current benchmark method. The MB assay, however, showed concentrations 1.9–3.1 times higher than the SBP and CIC assays. The extractable total PFAS concentrations in the real waters exceeded the sum of individual PFAS quantified by LC–MS, underscoring the necessity of identifying unknown PFAS.