A method of introducing and ejecting ions from an ion entry/exit device is disclosed. The ion entry/exit device has at least two arrays of electrodes. The device is operated in a first mode wherein DC potentials are successively applied to successive electrodes of at least one of the electrode arrays in a first direction such that a potential barrier moves along the at least one array in the first direction and drives ions into and/or out of the device in the first direction. The device is also operated in a second mode, wherein DC potentials are successively applied to successive electrodes of at least one of the electrode arrays in a second, different direction such that a potential barrier moves along the array in the second direction and drives ions into and/or out of the device in the second direction.