Mass spectrometry method and apparatus employing in-trap ion detection

Abstract

A mass spectrometry method and apparatus in which trapped ions of interest are detected as they strike a detector comprising at least one of the electrodes which establish the ion trapping field. The invention eliminates the need to eject ions from the trap, and thus eliminates the need to perforate one or more of the trap electrodes. In one class of preferred embodiments, the trapping field is a three-dimensional quadrupole trapping field within a region bounded by a ring electrode and a pair of end electrodes. In one embodiment, the inventive in-trap detector is a trap electrode composed (or partially composed) of phosphorescent material which emits photons in response to incidence of ions at its inward-facing surface (the surface of the electrode which faces the trap region). In another embodiment, the in-trap ion detector is a Faraday effect detector which includes an electrically isolated conductive pin mounted with its tip flush with the inward-facing surface of one of the trap electrodes.