U.S. Department of Energy

Pacific Northwest National Laboratory

Development and Evaluation of Long Serpentine Path Traveling Wave SLIM Modules for High Resolution Ion Mobility Separations

Introduction

Ion Mobility Spectrometry (IMS) is a well-established analytical method that is used to separate ionic species based on differences in their mobilities through buffer gas. One limiting feature of contemporary IMS technology is its limited ability to resolve different species with similar m/z. Conventional IMS instruments commonly have drift tubes of ~ 1m providing resolving powers of ~50-120. Although these platforms are sufficient for differentiation of chemical classes and determination of cross sections, many separations require much higher resolution. This presentation will focus on development and evaluation of a new novel high resolution IMS platform based upon a serpentine 13 m path length traveling wave Structures for Lossless Ion Manipulations (TW-SLIM) device.

 

Methods

The serpentine long path TW-SLIM module was fabricated using printed circuit board (PCB) technology, and consisted of a pair of parallel PCBs spaced by a small gap and having a 13 m long ion path, including 44-“U” turns and 2-90° turns. A pair of guard electrodes extend along the ion path and provide lateral ion confinement when an appropriate DC voltage is applied. RF voltages are applied to an array of 6 extended RF electrodes aligned with the ion path, creating pseudopotentials that prevent ion losses to the PCB surfaces. The TW potentials are applied to a separate set of electrodes that are positioned between the RF strips, and that drive ion motion to achieve ion mobility separations.

 

Preliminary data

We have developed and evaluated a 13 m long path TW-SLIM device for achieving lossless ion transmission along with robust performance and high resolution ion mobility separations. Using RF confinement orthogonal to the ion motion and a lateral static DC potential to prevent ion losses, and the application of TW potentials allows ions to be effectively moved and separated. The performance of long serpentine path TW-SLIM was found to be robust over extended periods (~8 hours). The ion mobility resolution of the TW-SLIM device was characterized over a wide range of pressures, SLIM PCB gaps, traveling wave and RF parameters. The resolution achieved was shown to be independent of guard electrode potential and RF amplitude; however, TW amplitude had significant effect on the resolution. Peak capacity and peak generation rate at 4 torr were estimated to be 176 and 264 s-1, respectively, at a optimum traveling wave speed of 148 m/s. Challenging separations were demonstrated revealing many new features, otherwise hidden by lower resolution IMS. This work has demonstrated a simple route for improving ion mobility resolution by increasing the length of ion path due to the lossless ion transmission enabled in SLIM devices. We anticipate that much longer ion paths and use of multi-pass cyclic TW-SLIM arrangements will further enhance the ion mobility resolution feasible, and enabling a broad range of applications that can be achieved with much greater throughput.

 

Novel aspect

High resolution ion mobility separations for biochemical molecules were achieved using 13 m long path TW-SLIM device

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