Performance Simulation of a Quadrupole Mass Filter Operating in the First and Third Stability Zones

A method of computation that accurately simulates the performance of quadrupole mass filters (QMFs) is described. Behavior is described by determining the individual trajectories of a large number of ions (10⁸) as they are injected into the QMF. The effects of the ratio of circular electrode radius r to electric field radius r0 on the performance characteristics have been investigated for zone 1 (a ap 0.237 and q ap 0.706) and zone 3 (a ap 3.16 and q ap 3.23) operation. We demonstrate that performance sensitivity to the r/r0 ratio is different for zone 3 than those previously reported for zone 1. The magnitude and variation of the ldquotailrdquo in the mass spectral peak shapes that are apparent for zone 1 is much decreased for zone 3 and does not influence QMF resolution. Variation in ion trajectories and associated power-spatial frequency spectra when operated in zones 1 and 3 with varying r/r0 geometrical ratios are also presented. We demonstrate that these provide an alternative method in determining an ideal value for r/r0.