Modified total oxidizable precursor assay for detecting per- and polyfluoroalkyl substances (PFAS) in complex media

Per- and Polyfluoroalkyl substances (PFAS) are a group of man-made chemicals having stable fluorinated alkyl chains that make them highly persistent and cause negative health impacts in humans and the environment. PFAS includes more than 4,700 chemicals consisting of fluorinated carbon tails with different functional head groups, of which only less than a hundred compounds are directly quantifiable due to the instrumental and reference standards constraints. Some “precursor PFAS” can transform biologically and abiotically, and TOP assays have been used in this context to accelerate the conversion of the precursor to terminal quantifiable PFAS, mainly Perfluoroalkyl acids (PFAAs), using thermal and chemical oxidation. Converted PFAAs can be easily measured using LC-MS/MS techniques so to indirectly detect PFAS precursors. However, the TOP assay was developed initially for clean matrices such as groundwater, and interferences of hydroxy radical reaction by the environmental matrices, especially that with high organic carbon was a known issue. Therefore, here we propose a modified version of the TOP assay to better facilitate PFAS analysis in complex samples including leachate, wastewater, and biosolids samples for this study. Samples were oxidized with hydrogen peroxide followed by TOP assay reagents. We observed a significant increase in PFAS detection as well as fewer interferences with our modified method. Hence, we conclude that this optimized method will improve the PFAS quantitation methods in various environmental samples.