Acid dissociation versus molecular association of perfluoroalkyl oxoacids: environmental implicationsAcid dissociation versus molecular association of perfluoroalkyl oxoacids: environmental implications Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2015-09-242009enPerfluorooctanoate (PFO) and perfluorooctanesulfonate (PFOS) surfactant anions, once released, may rapidly reach remote regions. This phenomenon is puzzling because the water-bound anions of strong F-alkyl acids should be largely transported by slow oceanic currents. Herein, we investigate whether these hydrophobic F-alkyl oxoanions would behave anomalously under environmental conditions, as suggested elsewhere. Negative electrospray ionization mass spectra of micromolar aqueous PFO or PFOS solutions from pH 1.0 to 6.0 show (1) m/z ) 499 (PFOS) signals that are independent of pH and (2) m/z ) 413 (PFO) and 369 (PFO - CO2) signals, plus m/z ) 213 (C F CO -) and 169 (C F -) signals at higher collision energies, and, below pH ∼ 372 37 4, m/z ) 827 signals from a remarkably stable (PFO)2H- cluster that increase with decreasing pH. Since the sum of the m/z ) 369, 413, and 827 signal intensities is independent of pH, that is, effectively encompasses all major species, we infer that pKa(PFOSA) < 1.0 and pKa(PFOA) < 1.0. We also derive K2 e 4 × 107 M-2 for the clustering equilibrium 2PFO + H+ h (PFO)2H. Thus, although (PFO)2H is held together by an exceptionally strong homonuclear covalent hydrogen bond, neither PFOS nor PFO will associate or protonate significantly at environmentally relevant subnanomolar concentrations above pH ∼ 1.http://creativecommons.org/licenses/by/4.0/The Journal of Physical Chemistry A113298152-8156 Psyllaki Eleftheria Ψυλλακη Ελευθερια Cheng Jie Colussi Arthur, Gabriella, 1957- Hoffmann M. R. ACS American Chemical Society Perfluoroalkyl oxoacids