Jens Griep-Raming et.al.: An Electrospray Ionization Source for the Investigation of Thermally Initiated Reactions

Author(s): Jens Griep-Raming, Juergen O. Metzger

Title: An Electrospray Ionization Source for the Investigation of Thermally Initiated Reactions

Date of Upload: 2000

Article: Anal. Chem.2000, 72,5665-5668, Department of Chemistry, University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany

Keywords: ESI-MS, electrospray ionization, mass spectrometry, reactive intermediate, reaction, solution, thermally initiated reactions, carbocations, radicals, scandium

Abstract:
An electrospray ionization source for mass spectrometry is described, which allows one to heat the spray capillary. Thermal dissociation of the trityl dimer 1 and tetra(panisyl) hydrazine (3) have been investigated, operating the ESI source as electrolytic cell to ionize neutral species, e.g. the trityl radical 2. Electrospray ionization (ESI) mass spectrometry (MS), introduced by Fenn et al.1 and Alexandrov et al.,2 has been shown to be useful for analysis of various kinds of analytes. With this technique, it became possible to analyze reaction substrates, products, and intermediates at the same time directly from reaction solutions. There are some examples in the literature that deal with organic reactions at room temperature,3-11 very few operating at temperatures below room temperature,12 but we found no publications that are concerned with the ESI investigation of reactions at elevated temperatures. As our work has been focusing on radical reactions13 and many radical reactions can be initiated by thermal decomposition of, for example, azo compounds or peroxides at elevated temperatures, we developed an ESI source that allows one to heat the reaction solution only a short time before the ionization occurs, or (even better) to heat the ionization region, thus enabling us to detect thermally generated reactive intermediates with very low steady-state concentration in the reaction solution. Because radicals are neutral species and are not ionized in the ESI process in general, we thought to operate the ESI source as an electrolytic cell as described by Van Berkel14. Thus, the thermally generated radicals should hopefully be oxidized electrolytically in situ to cations that can be observed by mass spectrometry. As first examples, we have investigated the behavior of the trityl dimer (1-diphenylmethylene-4-trityl-2,5-cyclohexadiene) (1) and of tetra(p-anisylhydrazine (3) at different temperatures.

URL: http://www.chemie.uni-oldenburg.de/oc/metzger/publikationen/pdf/88.pdf (application/pdf)


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