Leibniz University Hannover, Institute of Electrical Engineering and Measurement Technology, Appelstraße 9a, 30167 Hannover, Germany.
Department of Physical and Theoretical Chemistry, University of Wuppertal, Gauss Strasse 20, 42119 Wuppertal, Germany.
J Am Soc Mass Spectrom. 2020 Apr 1;31(4):812-821. doi: 10.1021/jasms.9b00087. Epub 2020 Feb 28.
In contrast to classical ion mobility spectrometers (IMS) operating at ambient pressure, the high kinetic energy ion mobility spectrometer (HiKE-IMS) is operated at reduced pressures between 10-40 mbar. In HiKE-IMS, ions are generated in a reaction region before they are separated in a drift region. Due to the operation at reduced pressure, it is possible to reach high reduced electric field strengths up to 120 Td in both the reaction as well as drift region, resulting in a pronounced decrease in chemical cross sensitivities and a significant enhancement of the dynamic range. Until now though, only limited knowledge about the ionization pathways in HiKE-IMS is available. Typically, proton bound water clusters, H(HO), are the most abundant positive reactant ion species in classical IMS with atmospheric chemical ionization sources. However, at reduced pressure and increased effective ion temperature, the reactant ion population significantly changes. As the ionization efficiency of analyte molecules in HiKE-IMS strongly depends on the reactant ion population, a detailed knowledge of the reactant ion population generated in HiKE-IMS is essential. Here, we present a coupling stage of the HiKE-IMS to a mass spectrometer enabling the identification of ion species and the investigation of ion molecule reactions prevailing in HiKE-IMS. In the present study, the HiKE-IMS-MS is used to identify positive reactant ion populations in both, purified air and nitrogen, respectively. The experimental data suggest the generation of systems of clustered primary ions (H(HO), NO(HO), and O(HO)), which most probably serve as reactant ions. Their relative abundances highly depend on the reduced electric field strength in the reaction region. Furthermore, their effective mobilities are studied as a function of the reduced electric field strength in the drift region.
与在环境压力下运行的经典离子淌度谱仪（IMS）相反，高动能离子淌度谱仪（HiKE-IMS）在 10-40 mbar 的减压下运行。在 HiKE-IMS 中，离子在漂移区分离之前在反应区中产生。由于在减压下操作，可以在反应区和漂移区中达到高达 120 Td 的高还原电场强度，从而导致化学交叉灵敏度显著降低，动态范围显著提高。尽管如此，到目前为止，对于 HiKE-IMS 中的电离途径，人们只有有限的了解。通常，质子结合水簇，H(HO)，是具有大气化学电离源的经典 IMS 中最丰富的正反应物离子种类。然而，在减压和增加有效离子温度的情况下，反应物离子种群会发生显著变化。由于 HiKE-IMS 中分析物分子的电离效率强烈依赖于反应物离子种群，因此对 HiKE-IMS 中产生的反应物离子种群有详细的了解是必不可少的。在这里，我们展示了将 HiKE-IMS 与质谱仪耦合的阶段，从而能够识别离子种类并研究在 HiKE-IMS 中占主导地位的离子-分子反应。在本研究中，使用 HiKE-IMS-MS 分别在净化空气和氮气中识别正反应物离子种群。实验数据表明，生成了簇状初级离子（H(HO)、NO(HO)和 O(HO)）的系统，它们很可能作为反应物离子。它们的相对丰度高度依赖于反应区中的还原电场强度。此外，还研究了它们的有效迁移率作为漂移区中还原电场强度的函数。
