Altering Conformational States of Dynamic Ion Populations using Traveling Wave Structures for Lossless Ion Manipulations

Abstract

With its capacity to store and translate ions across considerable distances and times, traveling wave structures for lossless ion manipulations (TW-SLIM) provide the foundation to expand the scope of ion mobility spectrometry (IMS) experiments. While promising, the dynamic electric fields and consequential ionneutral collisions used to realize extensive degrees of separation have a considerable impact on the empirical results and the fundamental interpretation of observed arrival time distributions. Using a custom-designed set of TW-SLIM boards (∼9 m) coupled with a time-of-flight mass spectrometer (SLIM-ToF), we detail the capacity to systematically alter the gas-phase distribution of select peptide conformers. In addition to discussing the role chargetransfer may play in TW-SLIM experiments that occur at extended time scales, the ability of the SLIM-ToF to perform tandem IMS was leveraged to confirm that both the compact and elongated conformers of bradykinin 2+ undergo interconversion within the SLIM. Storage experiments in which ions are confined within SLIM using static potential wells suggest that factors aside from TW-induced ion motion contribute to interconversion. Further investigation into this matter suggests that the use of radio frequency (RF) fields to confine ions within SLIM may play a role in ion heating. Aside from interconversion, storage experiments also provide insight into charge transfer behavior over the course of extended periods. The results of the presented experiments suggest that considerations should be taken when analyzing labile species and inform strategies for the TW-SLIM design and method development.

On the Arrival Time Distribution of Reacting Systems in Ion Mobility Spectrometry

“…This can also be understood in terms of ensemble mobility, ⟨ K ⟩ ens , as represented on the rhs of eq . On the other hand, slow or irreversible chemistry was observed in IMS for ion-neutral adduct formation at low neutral concentrations − or cold temperatures, the fragmentation of ions, , or conformational dynamics of flexible ions, ,,, all resulting in non-Gaussian peak shapes. Importantly, eq needs to be replaced by a more complex picture.…”