A mass analyzer (2) is provided comprising a plurality of electrodes having apertures through which ions are transmitted in use. A plurality of seudo-potential corrugations are created along the axis of the mass analyzer (2). The amplitude or depth of the pseudo-potential corrugations is inversely proportional to the mass to charge ratio of an ion. One or more transient DC voltages are applied to the electrodes of the mass analyzer (2) in order to urge ions along the length of the mass analyzer (2). The amplitude of the transient DC voltages applied to the electrodes is increased with time and ions are caused to be emitted from the mass analyzer (2) in reverse order of mass to charge ratio.
