An ion guide or ion trap 1 is disclosed comprising a segmented linear ion guide or ion trap. Ions are confined radially within the ion guide or ion trap 1 by the application of an AC or RF voltage to the electrodes. Ions are trapped within an axial quadratic potential well which is oscillated or modulated axially so as to cause ions to be ejected from the ion guide or ion trap 1 in a substantially non-resonant manner.