With quadrupolar excitation of ions by a small auxiliary RF field, the first stability region of the quadrupole mass filter splits into islands of stability. This study is of the first upper island, “A”. We calculate the location of this island for different values of the excitation parameter, q‘. Ion trajectory calculations are used to study the influence of the input fringing fields and the separation time. The Runge-Kutta–Nustrom–Dormand-Prince (RK–N–DP) method of order 6(7) is used for integration of the equations of ion motion. It is found that a weak auxiliary RF signal improves the peak shape for quadrupole mass filters that have weak field distortions.
