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Abstract

A mass spectrometry method in which an improved field comprising two or more trapping fields having substantially identical spatial form is established and at least one parameter of the improved field is changed to excite selected trapped ions sequentially, for example for detection. The improved field can also include a supplemental field of different spatial form. The changing improved field can sequentially eject selected ones of the trapped ions from the improved field for detection (or other purposes). An improved field comprising two quadrupole trapping fields can be established in a region defined by the ring and end electrodes of a three-dimensional quadrupole ion trap, and the amplitude of an RF (and/or DC) component (and/or the frequency of the RF component) of one or both trapping fields can be changed to sequentially excite trapped ions. Alternatively, a trapping field capable of storing ions having mass to charge ratio within a selected range is established, a supplemental field is superimposed with the trapping field to eject unwanted ions having mass-to-charge ratio within a second selected range from the improved field, the supplemental field having frequency components in one frequency range from a first frequency up to a notch frequency band and in another frequency range from the notch frequency band up to second frequency, and an improved field is then established by superimposing the trapping field with a second trapping field of substantially identical spatial form. Preferably, the relative phase of two or more component fields of the improved field is controlled to achieve an optimal combination of mass resolution, sensitivity, and mass peak stability.

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First Claim