Fast Atom Bombardment and Tandem Mass Spectrometry for Characterizing Fluoroalkanesulfonates

A series of perfluoroalkanesulfonates were examined by using fast atom bombardment (FAB) ionization combined with tandem mass spectrometry (MS/MS). Both positive and negative ion FAB spectra yield Information for determining molecular weight and identifying counterions. Abundant parent ions are desorbed and undergo minimal fragmentation. Structural information is obtained from the collision activated dissociation (CAD) spectra of selected parent ions. Comparisons of collisionally activated decompositions are made with hydrocarbon analogues. The fluoroalkanesulfonates undergo at least two remote charge site fragmentations. The more facile is loss of C_nF_2n+1 followed by losses of a perfluoroalkene. A second, less abundant series of fragments is formed by losses of the elements of C_nF_2n+2, a process that may be analogous to the parallel eliminations of the elements of C_nH_2n+2 from carboxylates and alkyl sulfates. Perfluoro alkanesulfonates containing a single hydrogen atom have also been determined by using FAB MS/MS and their fragmentation pathways elucidated. The combination of FAB and MS/MS should be useful for analysis of mixtures of fluorinated surfactants.