Mass spectrometry method using notch filter

Claim 1

A mass spectrometry method, including the steps of: (a) establishing a trapping field capable of storing parent ions and daughter ions having mass-to-charge ratio within a selected range within a trap region bounded by a set of electrodes; (b) applying a filtered noise signal to at least one of the electrodes to resonate out of the trap region unwanted ions having mass-to-charge ratio within a second selected range, wherein the trapping field is a three-dimensional quadrupole trapping field, wherein the electrodes include a ring electrode and a pair of end electrodes, wherein step (a) includes the step of applying a fundamental voltage signal to the ring electrode to establish the trapping field, and wherein step (b) includes the step of: applying the filtered noise signal to the ring electrode to resonate the unwanted ions out of the trap region in radial directions, toward the ring electrode, and wherein the selected range corresponds to a trapping range of ion frequencies, wherein the filtered noise signal has frequency components within a lower frequency range from a first frequency up to notch frequency band, and within a higher frequency range from the notch frequency band up to second frequency, wherein the frequency range spanned by the first frequency and the second frequency includes said trapping range, wherein the fundamental voltage signal has a radio frequency component and a DC component having an amplitude, wherein the amplitude of the DC component is chosen to establish both a desired low frequency cutoff and a desired high frequency cutoff for the trapping field, and wherein the first frequency is not significantly lower than the low frequency cutoff and the second frequency is not significantly higher than the high frequency cutoff.