title: Generation of ion-bound solvent clusters as reactant ions in dopant-assisted APPI and APLI.
abstract: We provide experimental and theoretical evidence that the primary ionization process in the dopant-assisted varieties of the atmospheric pressure ionization methods atmospheric pressure photoionization and atmospheric pressure laser ionization in typical liquid chromatography-mass spectrometry settings is--as suggested in the literature--dopant radical cation formation. However, instead of direct dopant radical cation-analyte interaction--the broadly accepted subsequent step in the reaction cascade leading to protonated analyte molecules--rapid thermal equilibration with ion source background water or liquid chromatography solvents through dopant ion-molecule cluster formation occurs. Fast intracluster chemistry then leads to almost instantaneous proton-bound water/solvent cluster generation. These clusters interact either directly with analytes by ligand switching or association reactions, respectively, or further downstream in the intermediate-pressure regions in the ion transfer stages of the mass spectrometer via electrical-field-driven collisional decomposition reactions finally leading to the predominantly observed bare protonated analyte molecules [M + H](+).
authors.affiliation: Physical and Theoretical Chemistry, Institute for Pure and Applied Mass Spectrometry, University of Wuppertal, Gaussstrasse 20, 42097 Wuppertal, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Klee
authors.forename: Sascha
authors.initials: S
authors.lastname: Albrecht
authors.forename: Valerie
authors.initials: V
authors.lastname: Derpmann
authors.forename: Hendrik
authors.initials: H
authors.lastname: Kersten
authors.forename: Thorsten
authors.initials: T
authors.lastname: Benter