Atmospheric pressure chemical ionization source. 1. Ionization of compounds in the gas phase

Francisco J. Andrade, Jacob T. Shelley, William C. Wetzel, Michael R. Webb, Gerardo Gamez Goytia, Steven J. Ray, Gary M. Hieftje

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Abstract

A novel chemical ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. The direct-current gas discharge is operated in helium at atmospheric pressure; typical operating voltages and currents are around 500 V and 25 mA, respectively. The species generated by this atmospheric pressure glow discharge are mixed with ambient air to generate reagent ions (mostly ionized water clusters and NO+), which are then used for the ionization of gaseous organic compounds. A wide variety of substances, both polar and nonpolar, can be ionized. The resulting mass spectra generally show the parent molecular ion (M+ or MH+) with little or no fragmentation. Proton transfer from ionized water clusters has been identified as the main ionization pathway. However, the presence of radical molecular ions (M+) for some compounds indicates that other ionization mechanisms are also involved.
Original languageEnglish
Pages (from-to)2646-2653
JournalAnalytical Chemistry
StatePublished - Apr 2008

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    Andrade, F. J., Shelley, J. T., Wetzel, W. C., Webb, M. R., Gamez Goytia, G., Ray, S. J., & Hieftje, G. M. (2008). Atmospheric pressure chemical ionization source. 1. Ionization of compounds in the gas phase. Analytical Chemistry, 2646-2653.