Untargeted Molecular Discovery in Primary Metabolism: Collision Cross Section as a Molecular Descriptor in Ion Mobility-Mass Spectrometry

Abstract

In this work we have established a collision cross section (CCS) library of primary metabolites based on analytical standards in the Mass Spectrometry Metabolite Library of Standards (MSMLS) using a commercially available ion mobility-mass spectrometer (IM-MS). From the 554 unique compounds in the MSMLS plate library, we obtained a total of 1246 CCS measurements over a wide range of biochemical classes and adduct types. Resulting data analysis demonstrated that the curated CCS library provides broad molecular coverage of metabolic pathways and highlights intrinsic mass/mobility relationships for specific metabolite super classes. The separation and characterization of isomeric metabolites were assessed, and all molecular species contained within the plate library, including isomers, were critically evaluated in order to determine the analytical separation efficiency in both the mass (m/z) and mobility (CCS/ΔCCS) dimension required for untargeted metabolomic analyses. To further demonstrate the analytical utility of CCS as an additional molecular descriptor, a well-characterized biological sample of human plasma serum (NIST SRM 1950) was examined by LC-IM-MS and used to provide a detailed isomeric analysis of carbohydrate constituents by ion mobility.

Molecular Level Analysis Reveals Changes in Chemical Composition of Dissolved Organic Matter From South Texas Rivers After High Flow Events

“…Given the current resolving power (ca. 60; Lu et al, 2018), this drift time ion mobility instrument is able to differentiate isomers with difference in CCS as low as 2% (Nichols et al, 2018). Note that a majority of molecules can be lost in the drift tube during the IM mode due to interactions with nitrogen gas (Lu et al, 2018).…”

“…Yellow oval indicates more extended compounds (less diagenetically altered) from high-flow samples. (Nichols et al, 2018). Therefore, isomer percentage was further defined as:…”

Ion mobility collision cross-section atlas for known and unknown metabolite annotation in untargeted metabolomics

“…Significant efforts have been made to curate large-scale experimental and calculated CCS databases 23 . For example, Baker group 24 and McLean group 25,26 measured chemical standards to construct experimental CCS databases with >1000 CCS values. Nevertheless, these CCS resources are reported in quite different formats, and lack appropriate procedures and tools for data collection, collation, standardization, and sharing.…”

Metabolic Phenotyping Using UPLC–MS and Rapid Microbore UPLC–IM–MS: Determination of the Effect of Different Dietary Regimes on the Urinary Metabolome of the Rat

“…Since its early beginnings in LC-MS-based metabolic phenotyping [19] the potential of IM, especially when combined with the CCS values derived from it, has been obvious, and both are increasingly being used in metabotyping (e.g., [5,6,[8][9][10][11][12]). However, whilst this trend is welcome, and the results obtained here employing the combination of t R , CCS are gratifying, the relatively low number of positive identifications does once again highlight a major problem for LC-MS-based metabolic phenotyping in that it is much easier to detect potential biomarkers than to actually convincingly identify them.…”

“…However, as well as this welcome increase in features, incorporation of IM can result in improved MS data as a result of the separation of co-eluting compounds and can also be used to determine the rotationally averaged collision cross section (CCS) of analytes. These CCS values, which represent a characteristic property of a molecule, provide a further means of improving the identification of metabolites detected in metabolic phenotyping studies in addition to MS [8][9][10][11][12].…”