Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, USA. hogan108@ umn.edu.
Analyst. 2017 May 21;142(10):1800-1812. doi: 10.1039/c7an00328e. Epub 2017 May 2.
Drift tube-ion mobility spectrometers (DT-IMSs) are used to separate and characterize the structures of gas phase ions. Recent work in coupling an atmospheric pressure DT-IMS to a condensation particle counter (CPC) has extended the application of drift tube ion mobility spectrometry to nanoparticle analysis, with measurements possible for singly charged particles up to 20 nm in diameter. In examining systems with such large analytes, often of interest is not only separation, but also determination of the nanoparticle size or mobility distribution function, defined as the nanoparticle concentration per unit mobility/size. Distribution function determination requires a priori knowledge of the DT-IMS transfer function, i.e. the DT-IMS combined transmission and detection efficiency as a function of both mobility and drift/arrival time. The transfer function completely describes analyte transport through an instrument; unfortunately, it has not been experimentally determined in previous work for a DT-IMS. Here, we develop and apply a new method to infer the transfer function of a DT-IMS-CPC system, wherein the system is used to measure particles which are first transmitted through a well-characterized differential mobility analyzer (DMA). The DMA acts as a mobility filter, and only transmits particles within a narrow, well-defined mobility range. From a series of measurements at fixed drift/arrival time (up to 12 seconds) but variable DMA transmission window, DT-IMS-CPC transfer functions are inverted via a Twomey-Markowski algorithm. Transfer function inversion reveals that the DT-IMS-CPC system has a resolving power in excess of 10 and upwards of 20. Such resolving powers are in good agreement with model predictions, and are higher than commercially available DMAs in the nanoparticle size range.
漂移管离子迁移谱仪（DT-IMS）用于分离和描述气相离子的结构。最近，将大气压 DT-IMS 与凝结核计数器（CPC）耦合的工作扩展了漂移管离子迁移谱在纳米颗粒分析中的应用，对于直径达 20nm 的单电荷颗粒可以进行测量。在研究具有如此大的分析物的系统时，通常不仅需要分离，还需要确定纳米颗粒的大小或迁移率分布函数，该函数定义为单位迁移率/大小的纳米颗粒浓度。分布函数的确定需要 DT-IMS 传递函数的先验知识，即 DT-IMS 的传输和检测效率作为迁移率和漂移/到达时间的函数。传递函数完全描述了分析物在仪器中的传输；不幸的是，在以前的工作中，DT-IMS 尚未通过实验确定。在这里，我们开发并应用了一种新方法来推断 DT-IMS-CPC 系统的传递函数，其中该系统用于测量首先通过特征良好的差分迁移率分析仪（DMA）传输的颗粒。DMA 充当迁移率滤波器，仅传输在狭窄、明确定义的迁移率范围内的颗粒。通过在固定漂移/到达时间（最多 12 秒）但可变 DMA 传输窗口的一系列测量中，通过 Twomey-Markowski 算法对 DT-IMS-CPC 传递函数进行反演。传递函数反演表明，DT-IMS-CPC 系统的分辨率超过 10，并且高达 20。这种分辨率与模型预测一致，并且在纳米颗粒尺寸范围内高于商用 DMA。
