Mass selective multinotch filter with orthogonal excision fields

摘要

A multinotch filter for selectively removing target ions with a plurality of specific mass-to-charge ratios from an ion beam is disclosed. The multinotch filter uses a quadrupole and a power supply for generating rf voltages in the quadrupole. The quadrupole has two pairs of parallel electrodes. Each pair has two parallel, oppositely facing electrodes. The rf voltages generated by the power supply includes a rf quadrupole frequency component and at least a first excision frequency component and a second excision frequency component. The rf quadrupole frequency component is applied to the electrodes such that within each pair the two oppositely facing electrodes with respect to the rf quadrupole frequency component are equal in potential and the two pairs are 180 DEG out of phase. With respect to the first excision frequency component, the oppositely facing electrodes within one pair are 180 DEG out of phase with each other. With respect to the second excision frequency component, the oppositely facing electrodes within the other pair are 180 DEG out of phase with each other. The quadrupole has an inlet end and an outlet end and the ion beam traverses from the inlet end to the outlet end. As a result of the rf quadrupole frequency component, ions of above a selected mass-to-charge ratio are guided down the quadrupole. The excision frequency components cause target ions of a plurality of specific mass-to-charge ratios to resonate and be removed from the ion beam before exiting the quadrupole.