Structural isomers of polyfluorinated di- and tri-alkylated phosphate ester surfactants present in industrial blends and in microwave popcorn bags

Introduction In this study, we provide strategies for detecting and quantifying the structural isomers of polyfluorinated di- and tri-alkyl surfactants (PFAS) by mass spectrometry (MS). We specifically investigate polyfluorinated dialkylated phosphate ester surfactants ( x :2/ y :2 diPAPS, (F(CF 2 ) x CH 2 CH 2 O-P(O)(O) − -OCH 2 CH 2 (CF 2 ) y F)) and their thioether analogues ( x :2/ y :2 S-diPAPS, F(CF 2 ) x CH 2 CH 2 SCH 2 -C[CH 2 O) 2 P(O)(O) − ]-CH 2 SCH 2 CH 2 (CF 2 ) y F), which are used for industrial applications, such as oil- and water-repellent coatings on paper and board. DiPAPS have been found in human blood and are metabolised to the persistent perfluoroalkyl carboxylic acids (PFCA) in rats. Materials and methods A microwave popcorn bag extract was analysed by ultrahigh-pressure liquid chromatography coupled to a negative electrospray ionisation-quadrupole time-of-flight MS. Results and discussion The extract contained S-diPAPS, diPAPS and trialkylated (triPAPS) impurities. TriPAPS were also present in industrial and synthetic diPAPS standards, and were verified with an 8:2/8:2/8:2 triPAPS standard. The eight elemental compositions ( m / z ’s) of diPAPS in the extract represent 19 precursor ion structures, and the six S-diPAPS m / z ’s represent at least 13 structures. The diPAPS had [M-H] − precursor ions of m / z 789, 889,…1,489 and the S-diPAPS of m / z 921, 1,021,…1,421, corresponding to fluorinated chains from C 6–18 . Each m / z appeared as one to three chromatographic peaks of structural isomers, where, e.g. m / z 1,189 was present as 10:2/10:2, 8:2/12:2 and 6:2/14:2 diPAPS. The isomers formed different products ions, thus only half of the m / z 1,189 diPAPS concentration was measured with one precursor ion > product ion transition. Conclusion In general, knowledge about structural isomers of poly-alkylated PFAS is needed for the estimation of types and amounts of perfluorinated degradation products, such as PFCA from diPAPS.