Quadrupole RF ion traps for mass spectrometers

Abstract

The invention relates to quadrupole RF ion traps used in a mass spectrometer, either as storage elements or as mass separators for the measurement of the mass spectrum of stored ions. The invention particularly relates to ion traps, which should show a pure quadrupole field without superimpositions of higher multipoles or, on the other hand, a quadrupole field with superimposition of one or several higher multipole fields of a precisely defined intensity, but no others, particularly no higher multipole fields. The limitation of ring and end cap electrodes to finite dimensions induces components of higher multipole fields within the ion trap, which may cause negative influences on the storage and scanning behavior. The invention consists of strongly suppressing the formation of higher multipole fields other than those required, by reduction of the gap width between the electrodes in the marginal area, compared to the gap width of electrodes modeled exactly according to the equipotential surfaces of the required field mixture of infinite expansion. A particularly strong suppression of higher multipole fields can be achieved by a wave-shaped constriction in the marginal area between the electrodes.

Dependencies are inferred from the claim text.