Schaefer Christoph, Schlottmann Florian, Kirk Ansgar T, Zimmermann Stefan
Department of Sensors and Measurement Technology, Institute of Electrical Engineering and Measurement Technology, Leibniz University Hannover, Appelstrasse 9A, 30167 Hannover, Germany.
J Am Soc Mass Spectrom. 2022 Jun 1;33(6):1048-1060. doi: 10.1021/jasms.2c00099. Epub 2022 May 20.
High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) chemically ionize gaseous samples via reactant ions and separate the generated ions by their motion in a neutral gas under the influence of an electric field. Operation at reduced pressures of 10-40 mbar allows for reaching high reduced electric field strengths (/) of up to 120 Td. At these high /, the generated ions gain the namesake high kinetic energies, leading to a decrease in cluster size of the reactant ions by increasing the reaction rate of collision-induced cluster dissociation of hydrates. In positive ion polarity and in purified air, HO(HO), NO(HO), and O(HO) are the most abundant reactant ions. In this work, we investigate the effect of varying sample gas humidity on product ion formation for several model substances. Results show that increasing the sample gas humidity at high / of 120 Td shifts product ion formation from a charge transfer dominated reaction system to a proton transfer dominated reaction system. For HiKE-IMS operated at high /, the reduction in cluster size of reactant ions allows ionization of analytes with low proton affinity even at high relative humidity in the sample gas of RH = 75% at 303.15 K and 1013.25 hPa. In contrast to conventional IMS, where increasing the sample gas humidity inhibits ionization for various analytes, increasing sample gas humidity in HiKE-IMS operated at 120 Td is actually beneficial for ionization yield of most analytes investigated in this work as it increases the number of HO(HO).
高动能离子迁移谱仪（HiKE - IMS）通过反应离子对气态样品进行化学电离，并在电场影响下，依据离子在中性气体中的运动情况对生成的离子进行分离。在10 - 40毫巴的减压条件下运行，可实现高达120 Td的高折合电场强度（/）。在这些高/值下，生成的离子获得了高动能，通过提高水合物碰撞诱导簇解离的反应速率，导致反应离子的簇尺寸减小。在正离子极性和净化空气中，HO(HO)、NO(HO)和O(HO)是最丰富的反应离子。在这项工作中，我们研究了不同样品气湿度对几种模型物质产物离子形成的影响。结果表明，在120 Td的高/值下增加样品气湿度，会使产物离子形成从电荷转移主导的反应体系转变为质子转移主导的反应体系。对于在高/值下运行的HiKE - IMS，反应离子簇尺寸的减小使得即使在303.15 K和1013.25 hPa、相对湿度RH = 75%的样品气中，低质子亲和力的分析物也能被电离。与传统IMS不同，在传统IMS中增加样品气湿度会抑制各种分析物的电离，而在120 Td下运行的HiKE - IMS中增加样品气湿度实际上有利于这项工作中所研究的大多数分析物的电离产率，因为它增加了HO(HO)的数量。
