Analysis of perfluoroalkyl anion fragmentation pathways for perfluoroalkyl carboxylates and sulfonates during liquid chromatography/tandem mass spectrometry: evidence for fluorine migration prior to secondary and tertiary fragmentation

It is known that under liquid chromatography/electrospray tandem mass spectrometry (LC/ES‐MS/MS) conditions, the perfluorocarboxylate anion [R F CO 2 ] − first loses CO 2 to give a perfluoroalkyl anion R   F − , [(MH)CO 2 ] − , which can subsequently fragment to give inter alia lower mass carbanions. It has been suggested in a previous study that such secondary fragmentation involves cleavage of C n F 2n segments. Our study of the LC/ES‐MS/MS of a series of 13 C‐labeled perfluoroalkyl carboxylic acids (PFCAs) indicates that fragmentation of the R   F −anion does not involve simple 'unzipping' of a primary perfluoroalkyl anion of the type F 3 C(CF 2 ) x CF   2 − . For example, we have discovered that the secondary transition for the mass‐labeled PFOA, perfluoro‐1,2,3,4‐ 13 C 4 ‐octanoic acid (MPFOA), gives two signals of equal intensity at m/z 169 and 172. We propose a mechanism of fragmentation that involves rapid fluorine shifts, after the initial decarboxylation, which generate a series of new anions prior to secondary and tertiary fragmentation. Copyright © 2007 John Wiley & Sons, Ltd.