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 C 3 H 6 O + . (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 N 2 O (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 + -alk, were also found to characterize isomeric epoxides as a result of either an initial electrophilic addition of the C 2 H 5 + cation (with saturated epoxides) or a methyl-transfer from [VME]+ . (with α, -unsaturated epoxides). The multiple tandem mass spectrometry (MS n ) capabilities of the ion trap were essential to achieve reagent ion mass-selection, structural assignment of the diagnostic-ions, or to provide further selectivity.

Low-Pressure Chemical Ionization in Ion Trap Mass Spectrometry

“…Nitrosonium ion CI has been implemented in an ion trap for the characterization of epoxides through the collisionally-activated dissociation of the hydride abstraction [M -H] + product ion generated under chemical ionization conditions. 88…”

“…Vinyl methyl ether is known to react through bimolecular processes leading to four-membered cyclic intermediate ions which can be used for the location of olefinic double bonds in mono-and poly-unsaturated compounds. 61,88 However, the use of pure vinyl methyl ether as reagent gas under high-pressure CI conditions allows the formation of charged protonated bound dimers and polymeric ions which complicate the interpretation of mass spectra. 61 Vinyl methyl ether plasmas, resulting from CI conditions, are known to be complicated by the diversity of chemical processes involved.…”

“…61 Vinyl methyl ether plasmas, resulting from CI conditions, are known to be complicated by the diversity of chemical processes involved. 88 As a consequence, isolation of the vinyl methyl ether radical cation, through a scanning sequence of the ion trap, simplifies the resulting CI spectra. Vinyl methyl ether was shown to yield molecular ions, resulting from charge transfer process, and [M + 15] + adduct ions, characteristic of a methyl transfer, with α,β-unsaturated epoxides providing, in combination with the MS n capabilities of the ion trap, an efficient selectivity for this class of compounds.…”

“…Vinyl methyl ether was shown to yield molecular ions, resulting from charge transfer process, and [M + 15] + adduct ions, characteristic of a methyl transfer, with α,β-unsaturated epoxides providing, in combination with the MS n capabilities of the ion trap, an efficient selectivity for this class of compounds. 88 Vinyl methyl ether has been proposed as an alkene-selective CI reagent for the implementation of a fast-response detection method for the measurement of atmospheric isoprene with a membrane introduction system coupled to an ion trap. 89 Ionized vinyl methyl ether molecular ion was proposed to react with the isoprene through a Diels-Alder cycloaddition process to form an unstable methoxycyclohexene radical cation which further fragments to lose methanol to generate an adduct ion [M + 58 -32] +• .…”

A Fast-Response Method for Determination of Atmospheric Isoprene Using Quadrupole Ion Trap Mass Spectrometry

“…VME/Isoprene CI Chemistry. The utility of VME as a selective reagent for olefinic functional groups has been well documented. − Compounds ranging from simple low-molecular-weight alkenes to much larger systems have been thoroughly examined. When VME is introduced into the quadrupole ion trap, the most abundant ions present are the acetyl cation ( m / z = 43) and the VME molecular ion ( m / z = 58).…”