U.S. Department of Energy

Pacific Northwest National Laboratory

Rectangular Ion Funnel (RIF): Conceptualization and Analytical Performance of a New ESI-MS Interface for Structures for Lossless Ion Manipulations (SLIM)

Introduction 

SLIM devices make use of capabilities for near lossless ion focusing, transfer, and trapping in regions of elevated pressure, and are advantageous for fast ion mobility separation and gas phase reactions. As advanced methods and instrumentation related to SLIM develop, the ion introduction through the ring electrode ion funnel to SLIM with rectangular lens entrance constitute additional technological challenges. Ions can experience discontinuities in electric fields that results in losses during transmission. In this work, we are investigating a new funnel that can seamlessly couple to SLIM devices with a proper electric field at the funnel exit. The newly designed RIF for SLIM essentially aims to achieve lossless ion introduction at elevated pressure region.

 

Methods

Initially, an ion simulation model was used to simulate the RIF which has one pair of the electrodes (x) on each lens independently connected to a dc power supply and another electrodes pair (y) on the same lens having an rf waveform applied for ion confinement. Adjacent electrodes in the axial direction have an rf waveform of equal amplitude but opposite phase for optimal ion confinement. A dc gradient was applied to the pairs of electrodes (x and y) that was continuously decreasing toward the end of the funnel to drive ions in the axial direction (z). For performance evaluation, the ions over wide m/z range were simulated in the RIF coupled to a PCB-based SLIM design.

 

Preliminary data

The newly designed RIF prototype consists of a stack of PCB fabricated lenses. Each lens has two electrode pairs forming a rectangle shape. The first 40 lenses has a dimension of 25x25 mm and the last 35 lenses dimensions decrease linearly from 25x25 mm to 5x5 mm (the same dimensions as the SLIM entrance). The RIF lenses are 0.75 mm thick and spaced 0.75 mm apart. The ion trajectory modeling was performed with SIMION 8.1 software with the Statistical Diffusion Simulation model for the ion mobility and diffusion at a pressure of 4 torr. In the simulation model, the RIF was synchronized with the first 4 trace electrodes of the SLIM board. The result shows a near-circular trapping potential in the region near the central of the RIF is similar to that from ion funnel with ring electrodes. The current approach to avoiding ion loss is to apply proper rf and dc bias on x and y pair of the electrodes for better ion confinement. With 1 MHz rf potential and 2 V dc bias, ion simulation results indicate 100% transmission efficiency for ions of m/z 50-1000 with an rf potential (100-200Vp-p,) and a dc gradient (4 to 30 V/cm) from the beginning of RIF lens to the fourth lens of the SLIM device.

 

Novel aspect

A newly designed rectangular ion funnel that is capable of highly efficient ion transmission into PCB-based SLIM devices.

 

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