Extracted fragment ion mobility distributions: A new method for complex mixture analysis

Abstract

A new method is presented for constructing ion mobility distributions of precursor ions based upon the extraction of drift time distributions that are monitored for selected fragment ions. The approach is demonstrated with a recently designed instrument that combines ion mobility spectrometry (IMS) with ion trap mass spectrometry (MS) and ion fragmentation, as shown in a recent publication [J. Am. Soc. Mass Spectrom. 22 (2011) 1477–1485]. Here, we illustrate the method by examining selected charge states of electrosprayed ubiquitin ions, an extract from diesel fuel, and a mixture of phosphorylated peptide isomers. For ubiquitin ions, extraction of all drift times over small mass-to-charge (m/z) ranges corresponding to unique fragments of a given charge state allows the determination of precursor ion mobility distributions. A second example of the utility of the approach includes the distinguishing of precursor ion mobility distributions for isobaric, basic components from commercially available diesel fuel. Extraction of data for a single fragment ion is sufficient to distinguish the precursor ion mobility distribution of cycloalkyl-pyridine derivatives from pyrindan derivatives. Finally, the method is applied for the analysis of phosphopeptide isomers (LFpTGHPESLER and LFTGHPEpSLER) in a mixture. The approach alleviates several analytical challenges that include separation and characterization of species having similar (or identical) m/z values within complex mixtures.

Gas-Phase Hydrogen-Deuterium Exchange Labeling of Select Peptide Ion Conformer Types: a Per-Residue Kinetics Analysis

“…Supplementary Figure 1 shows a schematic presentation of the instrument showing home-built components (ESI source, desolvation region, and drift tube) that have been coupled to a linear ion trap (LTQ Velos; ThermoScientific, San Jose, CA, USA). The instrument configuration is similar to that described in previous reports [28,29,51]. Electrosprayed peptide ions were stored in a Bhour-glass^ion funnel device [52] (Supplementary Figure 1), where they were periodically (20 ms) pulsed into a 1-m-long drift tube filled with~2.5 Torr of 300 K He buffer gas.…”

“…Drift Time Distributions (XIDTD) [51] As described previously [28], each t D -resolved mass spectrum was manually converted to a separate text file. An algorithm developed in-house linked t D values with each mass spectrum generating a three-column array text file of points with intensity (i) values above user-defined thresholds.…”

Chemometric Data Analysis for Deconvolution of Overlapped Ion Mobility Profiles

“…However, the analytical resolving powers (defined as the peak arrival time/full width at half height (FWHH)) of the current conventional IM-MS systems are limited to under~70 [9,10]. Often, the IM profiles of various ionic species with similar (or very close) collision cross sections (CCSs) are not completely resolved [11][12][13][14][15][16].…”

“…Employing a similar approach to conventional GC/MS peak deconvolution (viz., comparing single ion chromatograms (SIC) across a GC peak), Clemmer et al [11] and Cooper et al [12,13] utilized post-IM fragmentation techniques for deconvolution of mobility-overlapped profiles. Clemmer et al acquired post-IM/CID MS data for mass isolated mobility-overlapped isobaric precursor ions [11] and by inspecting the CID mass spectra across the mobility profiles of the mass isolated precursor ions, fragment ions specific to each species were identified.…”

“…Clemmer et al acquired post-IM/CID MS data for mass isolated mobility-overlapped isobaric precursor ions [11] and by inspecting the CID mass spectra across the mobility profiles of the mass isolated precursor ions, fragment ions specific to each species were identified. The resultant fragment IM profiles (referred to as the "extracted fragment ion drift time distributions (XFIDTD)") represented the AT distribution of each species [11].…”