An ion guide for transferring ions to a mass analyzer is disclosed. The ion guide is characterized in that a plurality of DC rings and a plurality of RF multi-pole rings with a plurality of electrodes are arranged alternatingly along a central axis between an inlet into which the ions move and an outlet for transferring the ions. The inner diameter of the DC rings is kept constant and the inner diameter of the RF multi-pole rings gradually decreases in a direction from the inlet to the outlet.