Institute of Electrical Engineering and Measurement Technology, Leibniz University Hannover, Appelstr. 9a, 30167 Hannover, Germany.
J Am Soc Mass Spectrom. 2023 May 3;34(5):893-904. doi: 10.1021/jasms.2c00365. Epub 2023 Mar 31.
High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) are usually operated at absolute pressures around 20 mbar in order to reach high reduced electric field strengths of up to 120 Td for influencing reaction kinetics in the reaction region. Such operating points significantly increase the linear range and limit chemical cross sensitivities. Furthermore, HiKE-IMS enables ionization of compounds normally not detectable in ambient pressure IMS, such as benzene, due to additional reaction pathways and fewer clustering reactions. However, operation at higher pressures promises increased sensitivity and smaller instrument size. In this work, we therefore study the theoretical requirements to prevent dielectric breakdown while maintaining high reduced electric field strengths at higher pressures. Furthermore, we experimentally investigate influences of the pressure, discharge currents and applied voltages on the corona ionization source. Based on these results, we present a HiKE-IMS that operates at a pressure of 60 mbar and reduced electric field strengths of up to 105 Td. The corona experiments show shark fin shaped curves for the total charge at the detector with a distinct optimum operating point in the glow discharge region at a corona discharge current of 5 μA. Here, the available charge is maximized while the generation of less-reactive ion species like NO is minimized. With these settings, the reactant ion population, HO and O, for ionizing and detecting nonpolar substances like -hexane is still available even at 60 mbar, achieving a limit of detection of just 5 ppb for -hexane.
高动能离子迁移谱仪（HiKE-IMS）通常在绝对压力约 20 毫巴下运行，以达到高达 120 Td 的高电场强度，从而影响反应区的反应动力学。这样的操作点显著增加了线性范围，并限制了化学交叉灵敏度。此外，HiKE-IMS 能够使在常压 IMS 中通常无法检测到的化合物如苯等进行电离，这是由于额外的反应途径和较少的团聚反应。然而，在更高的压力下操作有望提高灵敏度和减小仪器尺寸。在这项工作中，我们因此研究了在保持更高压力下的高电场强度的同时防止电介质击穿的理论要求。此外，我们还实验研究了压力、放电电流和施加电压对电晕电离源的影响。基于这些结果，我们提出了一种在 60 毫巴压力下工作并具有高达 105 Td 的电场强度的 HiKE-IMS。电晕实验显示出在辉光放电区具有明显最佳操作点的总电荷的鲨鱼鳍形状曲线，在该最佳操作点，电晕放电电流为 5 μA。在这里，在生成较少反应性离子物种（如 NO）的情况下，最大限度地增加了可用电荷。在这些设置下，即使在 60 毫巴下，仍可获得用于电离和检测非极性物质（如正己烷）的反应离子种群 HO 和 O，从而达到正己烷的检测限仅为 5 ppb。
