Ion gating in ion mobility spectrometry: Principles and advances

Linear drift tube ion mobility spectrometry (DTIMS) is widely used in standalone and hyphenated IMS instruments for detecting trace chemical compounds. As a temporal dispersion technique, DTIMS requires an ion injection process for generating discrete ion packets to start the ion mobility separation and detection steps. The ion injection process is carried out mainly via ion gating with ion gates of different mechanism and that defines largely the resolving power and the sensitivity of IMS analysis. This work is to present a systematic interpretation on the principles, limitations, and advances of ion gating in IMS. It mainly focuses on understanding the movement behaviors of ions around the ion gates along with the gating field changing actions and how to use such information fully to enhance the analytical performance of IMS. A summary description of the working principles and various configurations of ion gates will be presented first to comprehend the fundamentals of ion gating in IMS, followed by a discussion of the ion mobility discrimination arising from the non-idealities of ion gate as well as its effect on the ion packet injection process. Then, the dynamics of ion swarm in temporal and spatial varying electric fields would be explained mathematically and graphically to understand how ion gating under such conditions might affect the resolving power and the sensitivity of IMS. Further, advanced ion gating modes developed in the past decade for improving the analytical performance of IMS would be categorized and discussed along with analytical results. In the conclusion, perspectives on the current status and future development of ion gating in IMS would be provided. (C) 2020 Elsevier B.V. All rights reserved.