Patent ID: 8525108

Claim:
A mass spectrometry apparatus comprising: in a linear ion trap constructed of a plurality of quadrupole rod electrodes for performing mass-selective ejection, means for exciting ions along a first direction which orthogonally intersects a center axis of said rod electrodes; and means for forming an on-axis electric field along a second direction which orthogonally intersects the center axis of said rod electrodes and the first direction, wherein said first direction is a direction which connects a center of said quadrupole rod electrodes to an intermediate position of adjoining rod electrodes of said quadrupole rod electrodes, and wherein said means for forming the on-axis electric field along the second direction is means in which a direct current (DC) voltage is applied to a plurality of vane electrodes which are inserted between one pair of the adjoining rod electrodes of said quadrupole rod electrodes and whose distances from a center of said quadrupole rod electrodes vary.