A method of introducing and ejecting ions from an ion entry/exit device 4 is disclosed. The ion entry/exit device 4 has at least two arrays of electrodes 20,22. 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 20,22 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 20,22 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. The device provides a single, relatively simple device for manipulating ions in multiple directions. For example, the device may be used to load ions into or eject ions from an ion mobility separator in a first direction, and may then be used to cause ions to move through the ion mobility separator in the second direction so as to cause the ions to separate.