An ion mobility spectrometer (100) comprising a first ion source (102-1, 108-1) for providing positive ions to be analyzed, an electric field applier arranged to provide an electric field configured to move the positive ions in a first direction towards a first ion detector (106-1, 110-1) adapted for detecting the positive ions, and a second ion source (102-2, 108-2) for providing negative ions to be analyzed, wherein the electric field applier is arranged to move the negative ions in a direction opposite to the first direction, towards the first ion source (102-1, 108-1) and towards a second ion detector (106-1, 110-1) adapted for detecting the negative ions.