Abstract: A mass spectrometry method in which trapped ions are excited in non-consecutive mass order for detection. The ions can be ejected from the trap in non-consecutive mass order for detection at an external detector, or detected at an in-trap detector in non-consecutive mass order before they leave the trap. In one embodiment, a sequence of supplemental AC voltage signals, each having a frequency matching a resonant frequency of one of the ions to be detected, is applied to a trap to resonate trapped ions in non-consecutive mass order. In another embodiment, the amplitude of the fundamental RF trapping voltage is varied while a sequence of supplemental AC voltage signals is applied to a trap to resonate trapped ions (or cause them to become unstable) in non-consecutive mass order. Another embodiment enables detection of both high mass ions and low mass ions with improved high mass resolution, when the ions are stably trapped in a three-dimensional quadrupole trapped field.

Abstract: A mass spectrometry method in which notch-filtered noise is applied to an ion trap to resonate all ions except selected ions out of the region of the trapping field. Preferably, the trapping field is a quadrupole trapping field defined by a ring electrode and a pair of end electrodes positioned symmetrically along a z-axis, and the filtered noise is applied to the ring electrode to eject unwanted ions in radial directions rather than toward a detector mounted along the z-axis. Also preferably, the trapping field has a DC component selected so that the trapping field has both a high frequency and low frequency cutoff, and is incapable of trapping ions with resonant frequency below the low frequency cutoff or above the high frequency cutoff. Application of the filtered noise signal to such a trapping field is functionally equivalent to filtration of the trapped ions through a notched bandpass filter having such high and low frequency cutoffs.

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.