Thermal Production and Reactions of Organic Ions at Atmospheric Pressure

摘要

Ionization of nonvolatile compounds has been accomplished by a wide selection of desorption ionization (DI) methods in which the sample is converted from the condensed phase into vapor-phase ions by high-energy particles (neutral species or ions with energies of 5 keV-100 MeV), photon beams (UV or IR energy range), or high electric fields (ca. 1010 V m-1). Particular examples include secondary-ion mass spectrometry (SIMS),[1] fast atom bombardment (FAB),[2], [3] plasma desorption (PD),[4] laser desorption (LD),[5], [6] and field desorption (FD).[7] We now report a simple desorption method in which organic ions are generated efficiently by heating organic salts at atmospheric pressure; we also report reactions of these ions under ambient conditions. Although thermal ionization of low ionization energy elements is well-known,[8], [9] atmospheric-pressure thermal desorption ionization (APTDI) of organic ions, as reported here, is unprecedented. Appropriate choices of the matrix and solvent strongly increase ion intensities in APTDI. Significantly, atmospheric pressure ion-molecule reactions, which have relied on either radiolysis[10]-[12] or special high-pressure mass spectrometers,[13] now can be studied easily in the atmosphere by using thermally produced ions. Reactions in this pressure regime bridge condensed-phase and gas-phase ion chemistry.[10], [14]