Gas-Phase F-Atom Migration Reactions of Perfluoroalkyl and Polyfluoroalkyl Sulfonic/Sulfinic Anions

Many perfluoroalkyl and polyfluoroalkyl sulfonic/sulfinic acids and their derivatives are classified as perfluoroalkyl and polyfluoroalkyl substances (PFASs). The use of mass spectrometry techniques to analyze these compounds has attracted considerable research attention.

In this article, we employed high-resolution electrospray ionization tandem mass spectrometry (HR-ESI-MS/MS) and all-ion fragmentation (AIF) in negative ion mode to investigate gas-phase F-atom migration reactions of various perfluoroalkyl and polyfluoroalkyl sulfonic/sulfinic anions, particularly those yielding FSO₃ ^- or FSO₂ ^-.

HR-ESI-MS/MS of CF₃SO₃ ^- yielded an unexpected product ion FSO₃ ^-, representing a distinct pathway of gas-phase F-atom migration from C-atom to S-atom accompanied by the loss of CF₂. Similarly, HR-ESI-MS/MS of CF₃SO₂ ^- produced a dominant product ion FSO₂ ^- also via CF₂ elimination. Complementary ESI-MS/MS and AIF experiments on these anions confirmed that FSO₂ ^- and/or FSO₃ ^- are their characteristic fragmentation ions.

Theoretical calculations of gas-phase reactions CF₃SO₃ ^- → FSO₃ ^- + CF₂ and CF₃SO₂ ^- → FSO₂ ^- + CF₂ were performed to investigate the possible F-atom migration mechanisms. These results show that FSO₃ ^- at m/z 99 and/or FSO₂ ^- at m/z 83 could serve as diagnostic ions for structural elucidation of perfluoroalkyl and polyfluoroalkyl sulfonic/sulfinic acids and their derivatives in non-target PFASs analyses by using mass spectrometry.