title: Determination of ion mobility collision cross sections for unresolved isomeric mixtures using tandem mass spectrometry and chemometric deconvolution.
abstract: Ion mobility (IM) is an important analytical technique for determining ion collision cross section (CCS) values in the gas-phase and gaining insight into molecular structures and conformations. However, limited instrument resolving powers for IM may restrict adequate characterization of conformationally similar ions, such as structural isomers, and reduce the accuracy of IM-based CCS calculations. Recently, we introduced an automated technique for extracting "pure" IM and collision-induced dissociation (CID) mass spectra of IM overlapping species using chemometric deconvolution of post-IM/CID mass spectrometry (MS) data [J. Am. Soc. Mass Spectrom., 2014, 25, 1810-1819]. Here we extend those capabilities to demonstrate how extracted IM profiles can be used to calculate accurate CCS values of peptide isomer ions which are not fully resolved by IM. We show that CCS values obtained from deconvoluted IM spectra match with CCS values measured from the individually analyzed corresponding peptides on uniform field IM instrumentation. We introduce an approach that utilizes experimentally determined IM arrival time (AT) "shift factors" to compensate for ion acceleration variations during post-IM/CID and significantly improve the accuracy of the calculated CCS values. Also, we discuss details of this IM deconvolution approach and compare empirical CCS values from traveling wave (TW)IM-MS and drift tube (DT)IM-MS with theoretically calculated CCS values using the projected superposition approximation (PSA). For example, experimentally measured deconvoluted TWIM-MS mean CCS values for doubly-protonated RYGGFM, RMFGYG, MFRYGG, and FRMYGG peptide isomers were 288.8 Å(2), 295.1 Å(2), 296.8 Å(2), and 300.1 Å(2); all four of these CCS values were within 1.5% of independently measured DTIM-MS values.
authors.affiliation: Institute of Biomedical Studies, Baylor University, Waco, TX 76798, USA.
authors.forename: Brett
authors.initials: B
authors.lastname: Harper
authors.affiliation: Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, USA.
authors.forename: Elizabeth K
authors.initials: EK
authors.lastname: Neumann
authors.affiliation: Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA; Vanderbilt Institute of Chemical Biology, Nashville, TN 37235, USA; Vanderbilt Institute for Integrative Biosystems Research and Education, Nashville, TN 37235, USA; Center for Innovative Technology, Nashville, TN 37235, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Stow
authors.affiliation: Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA; Vanderbilt Institute of Chemical Biology, Nashville, TN 37235, USA; Vanderbilt Institute for Integrative Biosystems Research and Education, Nashville, TN 37235, USA; Center for Innovative Technology, Nashville, TN 37235, USA.
authors.forename: Jody C
authors.initials: JC
authors.lastname: May
authors.affiliation: Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA; Vanderbilt Institute of Chemical Biology, Nashville, TN 37235, USA; Vanderbilt Institute for Integrative Biosystems Research and Education, Nashville, TN 37235, USA; Center for Innovative Technology, Nashville, TN 37235, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: McLean
authors.affiliation: Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, USA. Electronic address: Touradj_Solouki@baylor.edu.
authors.forename: Touradj
authors.initials: T
authors.lastname: Solouki
keywords: Chemometric analysis; Collision-induced dissociation (CID); Ion mobility-mass spectrometry; Peak deconvolution; Resolving power; Structural isomers