Kirk Ansgar T, Kueddelsmann Maximilian J, Bohnhorst Alexander, Lippmann Martin, Zimmermann Stefan
Department of Sensors and Measurement Technology, Leibniz University Hannover, Institute of Electrical Engineering and Measurement Technology, Appelstrasse 9A, 30167 Hannover, Germany.
Anal Chem. 2020 Apr 7;92(7):4838-4847. doi: 10.1021/acs.analchem.9b04259. Epub 2020 Mar 24.
Field switching ion shutters allow generating short ion packets with high ion densities by first ionizing for several milliseconds in a field-free ionization region and then quickly pushing the entire ion population out into the drift region. Thus, they are an excellent choice for compact ion mobility spectrometers with both high resolving power and low limits of detection. Here, we present an improved setup, named the extended field switching ion shutter. By generating a second field-free region between the ionization region and the drift region, shielding of the ionization region is significantly improved, even when using grids with higher optical transparency to improve ion transmission into the drift region. Furthermore, it is shown that under certain conditions, ion transmission through multiple grids in series can even surpass transmission through a single grid of the same transparency. For the studied ions, the signal intensity at low concentrations increases by approximately a factor of 7 to 9 for protonated monomers, 10 to 14 for proton-bound dimers, and 25 for the proton-bound 1-octanol trimer compared to the classical field switching shutter. However, due to the nonlinear response for ions containing multiple analyte molecules, the limits of detection improve only by a factor of 3 to 4 for proton-bound dimers and 3 for the proton-bound 1-octanol trimer. Nevertheless, this still leads to single-digit ppt limits of detection for protonated monomers and hundred ppt limits of detection for proton-bound dimers measured for a series of ketones. However, for the most intense peaks such as the reactant ion peak, a significant loss of resolving power by a factor of up to 1.4 was observed due to Coulomb repulsion.
场切换离子快门通过先在无场电离区域电离数毫秒，然后迅速将整个离子群推出到漂移区域，从而允许产生具有高离子密度的短离子包。因此，它们是具有高分辨能力和低检测限的紧凑型离子迁移谱仪的绝佳选择。在此，我们展示了一种改进的装置，称为扩展场切换离子快门。通过在电离区域和漂移区域之间产生第二个无场区域，即使使用具有更高光学透明度的栅格来改善离子传输到漂移区域，电离区域的屏蔽也得到了显著改善。此外，结果表明，在某些条件下，串联通过多个栅格的离子传输甚至可以超过通过具有相同透明度的单个栅格的传输。对于所研究的离子，与传统场切换快门相比，低浓度下质子化单体的信号强度增加约7至9倍，质子键合二聚体增加10至14倍，质子键合1-辛醇三聚体增加25倍。然而，由于含有多个分析物分子的离子的非线性响应，质子键合二聚体的检测限仅提高3至4倍，质子键合1-辛醇三聚体提高3倍。尽管如此，这仍然导致一系列酮类物质中质子化单体的检测限达到个位数ppt，质子键合二聚体的检测限达到百位数ppt。然而，对于诸如反应物离子峰等最强峰，由于库仑排斥，观察到分辨能力显著损失高达1.4倍。
