ION EXCITATION IN A LINEAR ION TRAP WITH A SUBSTANTIALLY QUADRUPOLE FIELD HAVING AN ADDED HEXAPOLE OR HIGHER ORDER FIELD

摘要

A two-dimensional substantially quadrupole field is established and maintained to trap a selected group of ions. The field has a quadrupole harmonic with amplitude A<SUB>2</SUB>, and a higher order harmonic with an amplitude A<SUB>N</SUB>, A<SUB>N</SUB> being greater than 0.1%. The selected group of ions are trapped in the field. An oscillation frequency at a selected amplitude of excitation for the selected group of ions is determined. An excitation field at the selected amplitude of excitation is added to the two-dimensional substantially quadrupole field to deplete ions within a depletion peak having a low frequency side slightly above the oscillation frequency at the selected amplitude of excitation for the selected group of ions.