Molecular Descriptor on the Basis of Structural Analysis in Ion Mobility-Mass Spectrometry

Abstract

Ion mobility (IM) is an important electrophoretic technique where gas-phase ions are separated by their collision cross section (CCS). Often, it is integrated with mass spectrometry, allowing separation of both ion size and mass on millisecond timescales to create a high sensitivity, high throughput analytical technique. Reproducible properties such as CCS can be utilized as metrics for identification and characterization. Molecular size and mass scale predictably in these gas-phase measurements, creating class distinctions that aid in identification. Databases have been curated to allow improved identification of unknowns using descriptors such as mass and size and mapping IM class trends. Large databases of canonical CCS values demonstrate current trends in IM as well as new areas of exploration that will generate a significant impact. One area that has been relatively unexplored is the effect of drift gas on CCS. It has been noted that adjusting the ion mobility drift gas can affect these class distinctions. However, large scale studies had not been performed to investigate this effect across a wide mass and mobility range. This work demonstrates the value of ion mobility as a molecular descriptor in addition to mass spectrometry, establishes signposts for underexplored areas of study through a large database housing thousands of canonical CCS values, and further investigates one of these areas, exploring the effect of drift gas selection on CCS.