Patent ID: 7692143
Filing Date: 2010-04-06
Classification: H01J

Abstract:
1. A method of operating a mass spectrometer having an elongated rod set and a set of auxiliary electrodes, the rod set having an entrance end and an exit end and a longitudinal axis, the method comprising: a) admitting ions into the entrance end of the rod set; b) trapping at least some of the ions in the rod set by producing a barrier field at an exit member adjacent to the exit end of the rod set and by producing an RF field between the rods of the rod set, wherein the RF field and the barrier field interact in an extraction region adjacent the exit end of the rod set to produce a fringing field; and, c) providing an auxiliary ejection-inducing AC excitement voltage to the set of auxiliary electrodes to energize a first group of ions of a selected mass to charge ratio within the extraction region to mass selectively axially eject the first group of ions from the rod set past the barrier field; wherein the set of auxiliary electrodes comprises a plurality of segments spaced lengthwise along the mass spectrometer, the plurality of segments comprising an entrance segment set of auxiliary electrodes, a middle segment set of auxiliary electrodes and an exit segment set of auxiliary electrodes; the entrance segment set of auxiliary electrodes is between the middle segment set of auxiliary electrodes and the entrance end; the exit segment set of auxiliary electrodes is between the middle segment set of auxiliary electrodes and the exit end; step b) comprises trapping an entrance group of ions between the entrance segment set of auxiliary electrodes and an exit group of ions between the exit segment set of auxiliary electrodes, and providing a barrier voltage to the middle segment set of auxiliary electrodes to provide a barrier field between the entrance group of ions and the exit group of ions; and, step c) comprises i) providing the auxiliary ejection-inducing AC excitement voltage to the exit segment set of auxiliary electrodes to energize the ions of the selected mass to charge ratio within the extraction region to mass selectively axially eject the first group of ions from the rod set past the barrier field while retaining ions not of the selected mass to charge ratio.