Recommendations for reporting ion mobility mass spectrometry measurements

© 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc. Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide method-dependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc

The Use of Ion Mobility Mass Spectrometry for Isomer Composition Determination Extracted from Se-Rich Yeast

The isomer ratio determination of a selenium-containing metabolite produced by Se-rich yeast was performed. Electrospray ionization and ion mobility mass spectrometry (IM-MS) were unsuccessfully used in order to resolve the isomers according to their collisional cross section (CCS) difference. The isomer ratio determination of 2,3-dihydroxypropionylselenocystathionine was performed after multidimensional liquid chromatography preconcentration from a water extract of Se-rich yeast using preparative size exclusion, anion exchange, and capillary reverse phase columns coupled to IM-MS. 4′-nitrobenzo-15-crown-5 ether, a selective shift reagent (SSR), was added after the last chromatographic dimension in order to specifically increase the CCS of one of the isomers by the formation of a stable host–guest system with the crown ether. Both isomers were consequently fully resolved by IM-MS, and the relative ratio of the isomers was determined to be 11–13% and 87–89%. The present data compared favorably with the literature to support the analytical strategy despite the lack of an authentic standard for method validation. In addition, computational chemistry methods were successfully applied to design the SSR and to support the experimental data

The Use of Ion Mobility Mass Spectrometry for Isomer Composition Determination Extracted from Se-Rich Yeast

The isomer ratio determination of a selenium-containing metabolite produced by Se-rich yeast was performed. Electrospray ionization and ion mobility mass spectrometry (IM-MS) were unsuccessfully used in order to resolve the isomers according to their collisional cross section (CCS) difference. The isomer ratio determination of 2,3-dihydroxypropionylselenocystathionine was performed after multidimensional liquid chromatography preconcentration from a water extract of Se-rich yeast using preparative size exclusion, anion exchange, and capillary reverse phase columns coupled to IM-MS. 4′-nitrobenzo-15-crown-5 ether, a selective shift reagent (SSR), was added after the last chromatographic dimension in order to specifically increase the CCS of one of the isomers by the formation of a stable host–guest system with the crown ether. Both isomers were consequently fully resolved by IM-MS, and the relative ratio of the isomers was determined to be 11–13% and 87–89%. The present data compared favorably with the literature to support the analytical strategy despite the lack of an authentic standard for method validation. In addition, computational chemistry methods were successfully applied to design the SSR and to support the experimental data

Investigation of Structure-Stabilizing Elements in Proteins by Ion Mobility Mass Spectrometry and Collision-Induced Unfolding

A recently developed proteolytic reactor, designed for protein structural investigation, was coupled to ion mobility mass spectrometry to monitor collisional cross section (CCS) evolution of model proteins undergoing trypsin-mediated mono enzymatic digestion. As peptides are released during digestion, the CCS of the remaining protein structure may deviate from the classical 2/3 power of the CCS-mass relationship for spherical structures. The classical relationship between CCS and mass (CCS = A × M2/3) for spherical structures, assuming a globular shape in the gas phase, may deviate as stabilizing elements are lost during digestion. In addition, collision-induced unfolding (CIU) experiments on partially digested proteins provided insights into the CCS resilience in the gas phase to ion activation, potentially due to the presence of stabilizing elements. The study initially investigated a model peptide ModBea (3 kDa), assessing the impact of disulfide bridges on CCS resilience in both reduced and oxidized forms. Subsequently, β-lactoglobulin (2 disulfide bridges), calmodulin (Ca2+ coordination cation), and cytochrome c (heme) were selected to investigate the influence of common structuring elements on CCS resilience. CIU experiments probed the unfolding process, evaluating the effect of losing specific peptides on the energy landscapes of partially digested proteins. Comparisons of the TWCCSN2→He to trend curves describing the CCS/mass relationship revealed that proteins with structure-stabilizing elements consistently exhibit TWCCSN2→He and greater resilience toward CIU compared to proteins lacking these elements. The integration of online digestion, ion mobility, and CIU provides a valuable tool for identifying structuring elements in biopolymers in the gas phase