GEOMETRY FOR GENERATING A TWO-DIMENSIONAL SUBSTANTIALLY QUADRUPOLE FIELD

摘要

A method and apparatus for manipulating ions using a two­dimensional substantially quadrupole field, and a method of manufacturing an apparatus for manipulating ions using a two-dimensional substantially quadrupole field are described. The field has a quadrupole harmonic with amplitude A2, an octopole harmonic with amplitude A4, and higher order harmonics with amplitudes A6 and A8. The amplitude A8 is less than A4. The A4 component of the field is selected to improve the performance of the field with respect to ion selection and ion fragmentation. The selected A4 component can be added by selecting a degree of asymmetry under a 90° rotation about a central axis of the quadrupole. The degree of asymmetry is selected to be sufficient to provide the selected A4 component.