Allers Maria, Kirk Ansgar T, Timke Bennet, Erdogdu Duygu, Wissdorf Walter, Benter Thorsten, Zimmermann Stefan
Institute of Electrical Engineering and Measurement Technology, Leibniz University Hannover, Appelstraße 9a, 30167 Hannover, Germany.
Department of Physical and Theoretical Chemistry, University of Wuppertal, Gauss Str. 20, 42119 Wuppertal, Germany.
J Am Soc Mass Spectrom. 2020 Sep 2;31(9):1861-1874. doi: 10.1021/jasms.0c00126. Epub 2020 Aug 3.
Due to the operation at background pressures between 10-40 mbar and high reduced electric field strengths of up to 120 Td, the ion-molecule reactions in High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) differ from those in classical ambient pressure IMS. In the positive ion polarity mode, the reactant ions H(HO), O(HO), and NO(HO) are observed in the HiKE-IMS. The relative abundances of these reactant ion species significantly depend on the reduced electric field strength in the reaction region, the operating pressure, and the water concentration in the reaction region. In this work, the formation of negative reactant ions in HiKE-IMS is investigated in detail. On the basis of kinetic and thermodynamic data from the literature, the processes resulting in the formation of negative reactant ions are kinetically modeled. To verify the model, we present measurements of the negative reactant ion population in the HiKE-IMS and its dependence on the reduced electric field strength as well as the water and carbon dioxide concentrations in the reaction region. The ion species underlying individual peaks in the ion mobility spectrum are identified by coupling the HiKE-IMS to a time-of-flight mass spectrometer (TOF-MS) using a simple gated interface that enables the transfer of selected peaks of the ion mobility spectrum into the TOF-MS. Both the theoretical model as well as the experimental data suggest the predominant generation of the oxygen-based ions O, OH, O, and O in purified air containing 70 ppm of water and 30 ppm of carbon dioxide. Additionally, small amounts of NO and CO are observed. Their relative abundances highly depend on the reduced electric field strength as well as the water and carbon dioxide concentration. An increase of the water concentration in the reaction region results in the generation of OH ions, whereas increasing the carbon dioxide concentration favors the generation of CO ions, as expected.
由于在10 - 40毫巴的背景压力下运行以及高达120 Td的高折合电场强度，高动能离子迁移谱仪（HiKE - IMS）中的离子 - 分子反应与传统常压离子迁移谱中的反应不同。在正离子极性模式下，在HiKE - IMS中观察到反应物离子H(HO)、O(HO)和NO(HO)。这些反应物离子种类的相对丰度显著取决于反应区域的折合电场强度、操作压力以及反应区域中的水浓度。在这项工作中，详细研究了HiKE - IMS中负反应物离子的形成。基于文献中的动力学和热力学数据，对导致负反应物离子形成的过程进行了动力学建模。为了验证该模型，我们展示了HiKE - IMS中负反应物离子数量的测量结果及其对折合电场强度以及反应区域中水和二氧化碳浓度的依赖性。通过使用一个简单的门控接口将HiKE - IMS与飞行时间质谱仪（TOF - MS）耦合，该接口能够将离子迁移谱中选定的峰转移到TOF - MS中，从而识别离子迁移谱中各个峰所对应的离子种类。理论模型和实验数据均表明，在含有70 ppm水和30 ppm二氧化碳的纯净空气中，主要生成基于氧的离子O、OH、O和O。此外，还观察到少量的NO和CO。它们的相对丰度高度取决于折合电场强度以及水和二氧化碳的浓度。正如预期的那样，反应区域中水浓度的增加会导致OH离子的生成，而二氧化碳浓度的增加则有利于CO离子的生成。
