A comparison of three experimental techniques for ion structure studies via collision-induced reactions: The [C5H8]+˙ example

Structure differentiation between C₅H₈]⁺˙ ions, formed by electron ionization of various precursors, has been used as a test case for comparison of three experimental techniques involving collision-induced dissociation (CID). Low-energy CID in an rf-only quadrupole collision cell has been studied in the range 1–150 eV laboratory collision energy. These data have been compared with those obtained using mass-analyzed ion kinetic energy spectroscopy at 8 keV energy, and with results from dissociative charge-stripping (DCS) coupled with a second electron capture collision (EC) in order to remove intense interferences (DCS/EC). The greatest degree of structure differentiation was possible using the DCS/EC technique. The other two methods were comparable in this regard, although effects of pre-collision internal energy was apparent for collision energies much below 30 eV. Day-to-day reproducibility of spectra was most difficult to obtain for the low-energy CID technique. Of the C₅H₈]⁺˙ ions thus tested, the isoprene molecular ion was clearly the best match to the fragment ion formed from limonene.