An ion optical arrangement (1) for use in a mass spectrometer comprises a collision cell defining an ion optical axis along which ions may pass, electrodes comprising a set of parallel poles (11A, 11B, 11C) arranged in the collision cell, and a voltage source for providing voltages to the electrodes to produce electric fields. The ion optical arrangement is arranged for switching between a first operation mode in which the collision cell is pressurized and a second operation mode in which the collision cell is substantially evacuated. The ion optical arrangement is further arranged for producing a radio frequency electric focusing field in the first operation mode and a static electric focusing field in the second operation mode.