The mass-mobility correlation redux: The conformational landscape of anhydrous biomolecules

Abstract

Structural separations on the basis of gas-phase ion mobility-mass spectrometry are increasingly used for the analysis of complex biological samples. As a tool to elucidate biomolecular structure, ion mobility-mass spectrometry methods are unique in that direct molecular structural information is obtained for all resolved species, largely irrespective of the complexity of the sample. Computational approaches are used to interpret and discern structural details consistent with the empirical results. To a first approximation, correlations of mobility with mass allow for qualitative identification of the molecular class to which a particular species belongs. These correlations allow simultaneous characterization of different classes of biomolecules, which provides a means for combining omics measurements, such as lipidomics, proteomics, glycomics, and metabolomics, in the same analysis. Examination of the correlation of fine structure reveals that specific structural motifs, chemical functionality, chemical connectivity, and composition may also be determined, depending on the specific biomolecular class. Mapping the coarse and fine structure in ion mobility-mass spectrometry conformation space measurements provides an atlas for interpretation and discovery in complicated spectra. as-phase separations on the basis of migration and diffusion of ions through a neutral gas under the influence of an applied field have existed for over a century. The first examples of gasphase ion mobility (IM) include the quantitative studies of ionized gases by Rutherford shortly after the discovery of X-rays [1,2]. To place these early IM experiments in the context of mass spectrometry (MS), it would be almost another decade before J. J. Thomson would construct his first mass spectrograph [3]. Over the historic span of IMS development, the technique has been referred to by several names, including plasma chromatography [4], ion chromatography [5], and the currently accepted term ion mobility spectrometry (IMS). A detailed account on the historic development of IMS and milestones in the progress of gas-phase IM techniques is described elsewhere [6,7]. For many years, IMS separations were used for the fundamental study of atomic and small molecular ions in plasma physics. In the 1960s and 70s, a transition occurred from using IMS primarily as a fundamental physics research tool to using it as a separations device for analytical and physical chemistry applications. Notably, the early 1960s also marked the first reports of combining IMS with MS (IM-MS) [8,9].On the basis of these early IM-MS instruments, it was proposed that with proper calibration, IMS instruments could be operated as atmospheric pressure mass spectrometers in that mass could be assigned to a particular IM drift time [10,11]. This supposition was derived from plotting curves of mass as a function of mobility, which resulted in highly correlated calibration curves. However, this notion was qualified by Horning and colleagues in that highly correlated mass-mobility relat...

Correlating Resolving Power, Resolution, and Collision Cross Section: Unifying Cross-Platform Assessment of Separation Efficiency in Ion Mobility Spectrometry

“…4,62,63 Current mass analyzers are highly selective ( R p > 100,000), and, in many cases, accurate mass measurement when combined with tandem MS/MS capabilities can elucidate an analyte identification. However, when investigating analytical mixtures that possess isomers or investigating proteins which often express many conformers, ion mobility analysis is chemically insightful.…”

Increased ion transmission in IMS: A high resolution, periodic-focusing DC ion guide ion mobility spectrometer

“…Resolution is the most significant limitation of IMS for interrogation of complex biological mixtures whether for post-ionization separation, analytical applications, and/or structural characterization of ions which have similar ion-neutral collision cross sections [7,13]. Diffusion limited resolution is defined by Eq.…”

Structuring Microbial Metabolic Responses to Multiplexed Stimuli via Self-Organizing Metabolomics Maps

“…Technical triplicates of extracts were analyzed in a randomized sequence using UPLC-IM-MS (Waters Synapt G2, Milford, MA) with lock mass correction to provide accurate mass measurements. During each spectral acquisition, an intact and fragmentation spectrum was taken for all ions present (herein referred to as MS E analysis (Plumb et al, 2006)) (Goodwin et al, 2012; McLean, 2009). Fragmentation was performed subsequent to IM separation, which allowed for the correlation of product ions to precursor origins through matched mobility.…”