Mass‐selected reagent ion chemical ionization and multiple tandem mass spectrometry techniques in an ion trap mass spectrometer for structural analysis

Abstract

Mass-selected reagent ion chemical ionization (CI) performed in an ion trap instrument is an efficient tool to investigate gas-phase ion reactivities 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 alkenes. Regarding the assignment of epoxides, the previous NO+/CI method was adapted for an optimal use in the trap through isolation of NO+ cation from N2O (instead of NO) plasma and production of the acylium diagnostic-ions via CID of [M − H]+ formed by NO+-induced hydride abstraction. New alkylation ion-products, e.g. RCH = O+-al , were also found to characterize isomeric epoxides as a result of either an initial electrophilic addition of the C2H5+ cation (with saturated epoxides) or a methyl-transfer from [VME]+. (with α,β-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. © 1997 John Wiley & Sons, Ltd.