A study to understand the information gap between total organofluorine analysis and total oxidizable precursor assay on polyfluoroalkyl/perfluoroalkyl substances (PFASs)

Total oxidizable precursor (TOP) assay is an oxidation method to convert precursor compound of polyfluoroalkyl/perfluoroalkyl substances (PFASs) into measurable perfluorinated carboxylic acids (PFCAs). A previous mass balance study has shown that a loss of fluorine was observed after employing the method to convert the precursors in firefighting foams. Further, it has been seen that a large part of the total extractable organofluorine is still made up of compounds with unknown identity; ultra-short chain PFASs might have formed during the TOP assay, but they were not measured in the previous study. The aims of this investigation are to i) assess if the loss of fluorine in mass balance analysis is due to adsorption of the analyte to the reaction container used in the TOP assay and ii) investigate how much the ultra-short chain PFASs which were not measured in previous study contributes to the total amount of unidentifiable PFASs. TOP assay was performed on two commercially available fire-fighting foams, the same fire-fighting foams as the previous study. The analyses of PFASs were performed using ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) and ultra performance convergence chromatography mass spectrometry/mass spectrometry (UPC2-MS/MS) as well as combustion ion chromatography (CIC) to determine total organofluorine level. The results showed that for Sthamex AFFF, ultrasonicating the sample (during the oxidative reaction as well as after the reaction), gave an increase in total concentrations of PFAS between 16% and 46%. For the Arc Miljö fire-fighting foam sample, in contrast, no observable increase of total concentration of PFASs was observed. Ultra-short chain PFAS analysis of the two foams showed that ultra-short chain PFASs contributes less than 1% of the total concentration of identifiable PFASs.