title: Charge transfer dissociation (CTD) mass spectrometry of peptide cations using kiloelectronvolt helium cations.
abstract: A kiloelectronvolt beam of helium ions is used to ionize and fragment precursor peptide ions starting in the 1+ charge state. The electron affinity of helium cations (24.6 eV) exceeds the ionization potential of protonated peptides and can therefore be used to abstract an electron from--or charge exchange with--the isolated precursor ions. Kiloelectronvolt energies are used, (1) to overcome the Coulombic repulsion barrier between the cationic reactants, (2) to overcome ion-defocussing effects in the ion trap, and (3) to provide additional activation energy. Charge transfer dissociation (CTD) of the [M+H](+) precursor of Substance P gives product ions such as [M+H](2+•) and a dominant series of a ions in both the 1+ and 2+ charge states. These observations, along with the less-abundant a + 1 ions, are consistent with ultraviolet photodissociation (UVPD) results of others and indicate that C-C(α) cleavages are possible through charge exchange with helium ions. Although the efficiencies and timescale of CTD are not yet suitable for on-line chromatography, this new approach to ion activation provides an additional potential tool for the interrogation of gas phase ions.
authors.affiliation: Department of Forensic and Investigative Science, West Virginia University, Morgantown, WV, 26506, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Hoffmann
authors.forename: Glen P
authors.initials: GP
authors.lastname: Jackson
mesh_terms: D002412:Cations / Q000737:chemistry; D006371:Helium / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods*; D010455:Peptides / Q000032:analysis / Q000737:chemistry*
chemical_list: D002412:Cations; D010455:Peptides; D006371:Helium