Method Development towards Probing the Gut Metabolome using Reverse Phase Liquid Chromatography - Ion Mobility - Mass Spectrometry

Abstract

The aim of this research was to develop methods and strategies to use advancements in ion mobility-mass spectrometry to further metabolomic research. This work describes methods that have been developed to that end, with an emphasis on the gut metabolome. Ion mobility fits nicely into a traditional liquid chromatography-mass spectrometry work flow as it operates on the millisecond timescale. This allows ion mobility to enhance the separation of many of the biological classes that make up the metabolome simultaneously. Biological molecules travel through a mobility cell at speeds correlating to the number of inert gas collisions they experience. This allows the separation of molecules dependent on their gas-phase packing efficiency. This increase in separation capacity allows for the integration of all biological classes within one experimental method. A portion of this dissertation focused on the analysis of a class bile acids, small molecules found primarily in the enterohepatic circulation system. Many bile acids are isomers of each other and therefor difficult to distinguish in mass spectrometry as they have identical m/z and their polarities make them difficult to separate using liquid chromatography techniques as well. However, due to the gas phase interactions between the sterol and the tail, ion mobility allows these bile acids to be distinguished. This dissertation further demonstrates ion mobility’s utility in separating problematic isomers. Bile acid cross sections are then used to populate a CCS compendium to aid in the identification of compounds in complex biological mixtures. In addition, workflow was developed for a global, untargeted metabolomic platform that utilizes four descriptors (retention time, drift time, m/z, and fragmentation) to identify changes that are the result of biliary diversion surgery on mice. Fecal profiles of healthy controls were constructed from this metabolomic data and compared to two experimental surgical groups. In this, biological changes that result from bile acid dysregulation was discovered. This dissertation support the separation and analysis of metabolites derived from a complex sample aimed towards using this as a tool to understanding the microbiome.