Fourier transform mass spectrometer based on use of a fringing field to convert radial oscillations of excited ions to axial oscillations

Abstract

In one aspect, a mass analyzer is disclosed, which comprises a quadrupole having an input end for receiving ions and an output end through which ions can exit the quadrupole, said quadrupole having a plurality of rods to at least some of which an RF voltage can be applied for generating a quadrupolar field for causing radial confinement of the ions as they propagate through the quadrupole and further generating fringing fields in proximity of said output end. The mass analyzer further includes at least a voltage source for applying a voltage pulse to at least one of said rods so as to excite radial oscillations of at least a portion of the ions passing through the quadrupole at secular frequencies thereof, where the radially-excited ions interact with the fringing fields as they exit the quadrupole such that their radial oscillations are converted into axial oscillations.