PNNL

Abstract

The ion mobility spectrometry (IMS) is now taking its place among widely applied analytical methods. When coupled with mass spectrometers (MS), IMS becomes a powerful analytical tool for separating complex samples and investigating molecular structure, and improvements of IMS-MS instrumentation, e.g. to IMS resolving power and sensitivity, are highly desirable. Implementation of an ion trap for accumulation and pulsed ion injection to IMS based on the ion funnel has provided considerably increased ion currents, and thus a basis for improved sensitivity and (indirectly) measurement throughput. However, large ion populations may manifest Coulombic effects contributing to the spatial dispersion of ions traveling in the IMS drift tube, and thus affect IMS resolving power. In this study we present an analysis of Coulombic effects on IMS resolution. Basic relationships have been obtained for the spatial evolution of ion packets due to Coulombic repulsion. The theoretical relationships were compared with results of a computer model that simulates IMS operation based on a first principles approach. Initial experimental results reported here are consistent with the computer modeling and these relationships. A noticeable decrease of the IMS resolving power was observed for specific ion populations of >10,000 elementary charges. IMS operation conditions to minimize Coulombic effects, while minimizing sacrifices to performance, are discussed.