With support from the Chemical Measurement and Imaging program in the Chemistry Division, Professor Carlos Larriba-Andaluz at Indiana University-Purdue University in Indianapolis is working to improve our fundamental understanding of the principles of Ion Mobility Spectrometry (IMS), a technique that separates charged molecules through differences in their geometrical and electronic structure in the gas phase. This technique is utilized in a wide range of applications, such as airport security, health research, and environmental sciences. The Larriba-Andaluz group seeks to improve the performance of this important analysis tool by bridging the gap between classical assumptions and the influence of previously neglected secondary effects that are now known to have consequential impact on the performance of modern instruments. The impact of the research is enhanced through dissemination of user-friendly IMS software. An ancillary goal is expanding understanding of chemistry by outreach both to mechanical engineering students and to K-12 students. The outreach efforts especially seek to engage women and minorities, encouraging their participation in science and engineering.

IMS is becoming an integral part of modern mass spectrometry (MS). This has resulted in important advances in IMS instrumentation with improved resolution, transmission, and sensitivity. Despite these advances, there has not been a parallel improvement in understanding the underlying theory. The problem is challenging, because IMS separates analytes based on size over charge, where the size is an intricate combination of gas parameters, forces applied and potential interactions between ion and buffer gas. As IMS instruments reach resolving powers of several hundreds, the existing simplified theory will often prove inadequate. By means of relaxing Chapman and Cowling's first collision integral theory, Professor Larriba-Andaluz and his team are 1) evaluating the effect of high field to density ratios, permanent dipole moments, and preferred orientations; 2) addressing the elastic/diffuse inelastic nature of the impingement-reemission collision theory through the coupling of quantum mechanics (QM) and molecular dynamics(MD) to kinetic theory; and 3) assessing collision cross section (CCS) modification due to ion structure compaction in the gas phase. The aims are to 1) improve existing theoretical knowledge in the free molecular regime through relaxation of linearization of the momentum transfer equations; 2) study momentum exchange upon impingement, thereby improving understanding of how energy exchange occurs at the molecular level; and 3) close the existing gap between novel existing IMS systems and the theoretical understanding of how separation occurs in them. Free dissemination of the algorithms developed should spur development of new calculations, leading to better optimization and development of instrumentation, and the emergence of new applications in imaging for complex samples.

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.

National Science Foundation (NSF)
Division of Chemistry (CHE)
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Kelsey Cook
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Indiana University
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