METHOD OF OPERATING QUADRUPOLES WITH ADDED MULTIPOLE FIELDS TO PROVIDE MASS ANALYSIS IN ISLANDS OF STABILITY

摘要

A method of processing ions in a quadrupole rod set usprovided. The method comprises a) establishing and maintaining a two-dimensional substantially quadrupole field for processing the ions, the fieldhaving a quadrupole harmonic with amplitude A2 and a selected higher orderharmonic with amplitude Am wherein m is an integer greater than 2, and themagnitude of Am is greater than 0.1% of the magnitude of A2; b)introducingthe ions to the two-dimensional substantially quadrupole field and subjectingthe ions to both the quadrupole harmonic and the higher order harmonic ofthe field to radially confine ions having Mathieu parameters a and q within astability region defined in terms of the Mathieu parameters a and q; c) addingan auxiliary excitation field to transform the stability region into aplurality ofsmaller stability islands defined in terms of the Mathieu parameters a and q;and, d) adjusting the two-dimensional substantially quadrupole field to placeions within a selected range of mass-to-charge ratios within a selectedstability island in the plurality of stability islands to impart stabletrajectories tothe selected ions within the selected range of mass-to-charge ratios fortransmission through the rod set, and to impart unstable trajectories tounselected ions outside of the selected range of mass-to-charge ratios tofilterout such ions.