Development of a Spatially Multiplexed Ion Mobility Spectrometer and Utilization of Ion Mobility-Mass Spectrometry for Conformational Analyses of Lipids and Other Biomolecules
Leaptrot, Katrina Lahoma
The aim of this research was to develop strategies to advance ion mobility-mass spectrometry (IM-MS) studies via both the development of a novel, spatially multiplexed instrument and the conformational analyses of biomolecules, specifically in regards to lipid structural identification. This work describes the theoretical considerations and development of a novel multiplexed ion mobility spectrometer (IM), which can be interfaced with mass spectrometry (MS) in the future and will provide benefits in throughput, sensitivity, versatility, and temporal sampling resolution (for on-line analyses), among other figures-of-merit. The spatially multiplexed IM consists of arrays of eight ion sources, optical components, and detectors, with all components housed in a single vacuum system, utilizing one set of electronics, and supported by shared hardware. This instrument is currently undergoing evaluation, modification, and optimization, with ions having been successfully generated, transmitted into vacuum, manipulated via ion optics, and detected at a Faraday plate, and the acquired signal having been displayed by means of software developed in-house. A commercially available IM-MS was used for comparison of collision cross section (CCS) and mass-to-charge ratio. Analyses across four chemically distinct classes of molecules revealed relative gas-phase densities as follows, from least to most efficient packing: tetraalkylammonium salts, lipids, peptides, and carbohydrates. Of the investigated biomolecules, lipids exhibited the largest CCS values, intrinsic to their inability to form compact gas-phase structures. The biological function of lipids is dictated by structure, making elucidation of their structural detail an important endeavor. Seven lipid classes within glycerophospholipid and sphingolipid categories were investigated and found to trend uniquely relative to headgroup size, with adoption of general and predictable gas-phase conformations governed by differences within the acyl tails, of which the degree of unsaturation was found to be four times as influential as acyl chain length on conformational broadening.