title: Atmospheric pressure chemical ionization of explosives induced by soft X-radiation in ion mobility spectrometry: mass spectrometric investigation of the ionization reactions of drift gasses, dopants and alkyl nitrates.
abstract: A promising replacement for the radioactive sources commonly encountered in ion mobility spectrometers is a miniaturized, energy-efficient photoionization source that produce the reactant ions via soft X-radiation (2.8 keV). In order to successfully apply the photoionization source, it is imperative to know the spectrum of reactant ions and the subsequent ionization reactions leading to the detection of analytes. To that end, an ionization chamber based on the photoionization source that reproduces the ionization processes in the ion mobility spectrometer and facilitates efficient transfer of the product ions into a mass spectrometer was developed. Photoionization of pure gasses and gas mixtures containing air, N2, CO2and N2O and the dopant CH2Cl2is discussed. The main product ions of photoionization are identified and compared with the spectrum of reactant ions formed by radioactive and corona discharge sources on the basis of literature data. The results suggest that photoionization by soft X-radiation in the negative mode is more selective than the other sources. In air, adduct ions of O2-with H2O and CO2were exclusively detected. Traces of CO2impact the formation of adduct ions of O2-and Cl-(upon addition of dopant) and are capable of suppressing them almost completely at high CO2concentrations. Additionally, the ionization products of four alkyl nitrates (ethylene glycol dinitrate, nitroglycerin, erythritol tetranitrate and pentaerythritol tetranitrate) formed by atmospheric pressure chemical ionization induced by X-ray photoionization in different gasses (air, N2and N2O) and dopants (CH2Cl2, C2H5Br and CH3I) are investigated. The experimental studies are complemented by density functional theory calculations of the most important adduct ions of the alkyl nitrates (M) used for their spectrometric identification. In addition to the adduct ions [M + NO3]-and [M + Cl]-, adduct ions such as [M + N2O2]-, [M + Br]-and [M + I]-were detected, and their gas-phase structures and energetics are investigated by density functional theory calculations. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Physical Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Riebe
authors.affiliation: Physical Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Erler
authors.affiliation: Physical Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ritschel
authors.affiliation: Physical Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam, Germany.
authors.forename: Toralf
authors.initials: T
authors.lastname: Beitz
authors.affiliation: Physical Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam, Germany.
authors.forename: Hans-Gerd
authors.initials: HG
authors.lastname: Löhmannsröben
authors.affiliation: Bruker Daltonik, Permoserstrasse 15, Leipzig, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Beil
authors.affiliation: Bruker Daltonik, Permoserstrasse 15, Leipzig, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Blaschke
authors.affiliation: Bruker Daltonik, Permoserstrasse 15, Leipzig, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ludwig
keywords: X-ray; alkyl nitrates; explosives; ion mobility spectrometry; mass spectrometry; photoionization