Applications of a travelling wave‐based radio‐frequency‐only stacked ring ion guide

TLDR

RF‑only ion guides are widely used in mass spectrometry to transport ions through high‑pressure regions, but collisions that aid fragmentation can also slow axial ion velocity, and current guides typically employ multipole rod sets. This study investigates a new ion propulsion mode in an RF ion guide that uses a stack of ring electrodes. Ion propulsion is achieved by superimposing a voltage pulse on the guiding RF, then sequentially shifting the pulse along adjacent ring electrodes to generate a travelling voltage wave that ions can surf. With suitable travelling‑wave pulse height, velocity, and gas pressure, the stacked‑ring guide functions as an effective collision cell for rapid mass scanning, an ion‑mobility separator at ~0.2 mbar, an ion‑delivery device that boosts duty cycle on oa‑TOF analyzers, and a fragmentation device at higher wave speeds. © 2004 John Wiley & Sons, Ltd.

Abstract

Abstract The use of radio‐frequency (RF)‐only ion guides for efficient transport of ions through regions of a mass spectrometer where the background gas pressure is relatively high is widespread in present instrumentation. Whilst multiple collisions between ions and the background gas can be beneficial, for example in inducing fragmentation and/or decreasing the spread in ion energies, the resultant reduction of ion axial velocity can be detrimental in modes of operation where a rapidly changing influx of ions to the gas‐filled ion guide needs to be reproduced at the exit. In general, the RF‐only ion guides presently in use are based on multipole rod sets. Here we report investigations into a new mode of ion propulsion within an RF ion guide based on a stack of ring electrodes. Ion propulsion is produced by superimposing a voltage pulse on the confining RF of an electrode and then moving the pulse to an adjacent electrode and so on along the guide to provide a travelling voltage wave on which the ions can surf. Through appropriate choice of the travelling wave pulse height, velocity and gas pressure it will be shown that the stacked ring ion guide with the travelling wave is effective as a collision cell in a tandem mass spectrometer where fast mass scanning or switching is required, as an ion mobility separator at pressures around 0.2 mbar, as an ion delivery device for enhancement of duty cycle on an orthogonal acceleration time‐of‐flight (oa‐TOF) mass analyser, and as an ion fragmentation device at higher wave velocities. Copyright © 2004 John Wiley & Sons, Ltd.