MASS-SELECTED REAGENT ION CHEMICAL-IONIZATION AND MULTIPLE TANDEM MASS-SPECTROMETRY TECHNIQUES IN AN ION-TRAP MASS-SPECTROMETER FOR STRUCTURAL-ANALYSIS

Mass-selected reagent ion chemical ionization (CI) performed in an ion trap instrument is an efficient tool to investigate gas-phase ion rea ctivities and therefore to find out new and/or optimized applications for structural analysis, For instance, it was shown that the C3H6O+. ( 58 mass units) molecular ion originated from vinyl methyl ether (VME) should necessarily be used alone (i.e. unit-mass selected) to produce significant diagnostic-ions for double bond location in aliphatic alke nes. Regarding the assignment of epoxides, the previous NO+/Cl method was adapted for an optimal use in the trap through isolation of NO+ ca tion from N2O (instead of NO) plasma and production of the acylium dia gnostic-ions via CID of [M-H](+) formed by NO+-induced hydride abstrac tion. New alkylation ion-products, e.g. RCH = O+-alk, were also found to characterize isomeric epoxides as a result of either an initial ele ctrophilic addition of the C2H5+ cation (with saturated epoxides) or a methyl-transfer from [VME](+.) (with alpha,beta-unsaturated epoxides) . The multiple tandem mass spectrometry (MSn) capabilities of the ion trap were essential to achieve reagent ion mass-selection, structural assignment of the diagnostic-ions, or to provide further selectivity. (C) 1997 by John Whey & Sons, Ltd.