title: Structural isomers of polyfluorinated di- and tri-alkylated phosphate ester surfactants present in industrial blends and in microwave popcorn bags.
abstract: BACKGROUND
  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.
  
  
  METHODS
  A microwave popcorn bag extract was analysed by ultrahigh-pressure liquid chromatography coupled to a negative electrospray ionisation-quadrupole time-of-flight MS.
  
  
  CONCLUSIONS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Basic Sciences and Environment, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg, Denmark. xttr@food.dtu.dk
authors.forename: Xenia
authors.initials: X
authors.lastname: Trier
authors.forename: Nikoline Juul
authors.initials: NJ
authors.lastname: Nielsen
authors.forename: Jan H
authors.initials: JH
authors.lastname: Christensen
mesh_terms: D000478:Alkylation; D004784:Environmental Monitoring; D004952:Esters / Q000032:analysis / Q000737:chemistry; D005506:Food Contamination / Q000032:analysis*; D018857:Food Packaging; D054879:Halogenation; D010710:Phosphates / Q000032:analysis* / Q000737:chemistry; D013501:Surface-Active Agents / Q000032:analysis* / Q000737:chemistry
chemical_list: D004952:Esters; D010710:Phosphates; D013501:Surface-Active Agents