High Resolution Ion Mobility Spectrometry with Increased Ion Transmission: Exploring the Analytical Utility of Periodic-Focusing DC Ion Guide Drift Cells
Blase, Ryan Christopher
MetadataShow full item record
Drift tube ion mobility spectrometry (IMS) is a powerful, post-ionization separation that yields structural information of ions through an ion-neutral collision cross section. The ion-neutral collision cross section is governed by the collision frequency of the ion with the neutral drift gas. Consequently, ions of different size will have different collision frequencies with the gas and be separated in the drift cell. A significant challenge for IMS, however, is to separate ions with very similar collision cross sections, requiring higher resolution ion mobility spectrometers. Resolution in IMS is of utmost importance for the separation of complex mixtures, e.g. crude oil samples, proteolytic digests, positional isomers, and ion conformers. However, most methods employed to increase mobility resolution significantly decrease ion transmission through the mobility device. Herein, a periodic-focusing DC ion guide drift cell (PDC IG) is presented to display its potential capabilities for higher mobility resolution with increased ion transmission. The PDC IG utilizes unique electrode geometry compared to the conventional uniform field electrode design. Electrode geometry can be defined by the electrode inner diameter (d), thickness (t), and spacing (s). Specifically, the ratio of d : t : s is equal to, or very near, 1:1:1. The PDC IG electrode design creates a non-uniform (fringing) electric field-especially near the electrode walls. The design also causes variations in the radial electric field which provides an effective RF as ions move through the device and a radially confining effective potential that improves ion transmission through the device. In this dissertation the analytical utility of the PDC IG drift cell for ion mobility separations will be explored. The radial focusing properties of the device will be presented along with studies of electrode geometry and its effect on ion mobility resolution and ion transmission through the drift cell. PDC IG drift cell length is also examined to determine its effect on mobility resolution and ion transmission. Finally, the PDC IG drift cell device is coupled to an orthogonal-acceleration time-of-flight mass spectrometer as well as a modular, PDC IG drift cell being adapted to a commercial qTOF mass spectrometer for IM-MS experiments.