A mass spectrometer is disclosed comprising an ion guide or ion mobility spectrometer having helical, toroidal, part-toroidal, hemitoroidal, semitoroidal or spiral ion guiding region. The ion guide may comprise a tube made from a leaky dielectric wherein an RF voltage is applied to outer electrodes in order to confine ions radially within the ion guide. A DC voltage is applied to a resistive inner layer in order to urge ions along the ion guide. Alternatively, the ion guide may comprise a plurality of electrodes each having an aperture through which ions are transmitted.