CDS&E: Theoretical, Numerical and Experimental Analysis of Gas-Ion Energy Exchange in Ion Mobility for the Separation of Polyatomic Ions

Indiana University, Bloomington IN

Investigators

Abstract

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Carlos Larriba-Andaluz and his group at Indiana University-Purdue University in Indianapolis are working on improving the understanding of how ionic compounds may be separated and characterized in the gas phase via a technique known as Ion Mobility Spectrometry (IMS). Understanding how this separation occurs is not only vital to analytical chemistry, but also to aerosol science and plasma physics. One of the reasons that IMS has become quite relevant is that it is able to distinguish ions that have the same mass but different shapes, known as isomers. Distinguishing isomers is extremely important - small changes in shape can result in drastic changes in chemical and physical properties. In fact, IMS systems have arrived at such sophistication that the existing theory is incapable of describing some of the observed separation capabilities. The Larriba-Andaluz group is working to fill this knowledge gap through novel theoretical approaches and numerical tools. The team is engaging undergraduate students, including members of underrepresented groups, through summer courses. They are also developing online IMS training materials to captivate both new and seasoned users. Ion Mobility Spectrometry (IMS) is becoming one of techniques most employed in combination with Mass Spectrometry (MS). As IMS systems become more sensitive and accurate, commonly used modeling and theory approximations have been unable to explain some recently observed capabilities, including separations of isomers, isotopologues, and even isotopomers. Interchange of energy between translational and internal degrees of freedom accompanying ion-molecule collisions is a potential contributor to these phenomena which has not yet been incorporated into existing theories. The Larriba-Andaluz group is investigating the mechanism and role of this energy exchange under conditions of varying electric field and temperature. Specifically, they are developing 1) higher-order ion mobility approximations using two-temperature theory, followed by the inclusion of ion energy calculations and inelasticity effects, and 2) models of mobility and energy balance using an in-house Molecular Dynamics-Monte Carlo hybrid code. Comparison of experimental results at different fields and temperatures is being used to predict the effect of inelastic contributions. The resulting insights are expected to help explain the remarkable separation ability of ion mobility spectrometry and to broadly advance the field of ion mobility. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.