US Patent 7851743 Ion mobility spectrometer

The present invention achieves an ion mobility spectrometer which is small-sized but has higher selectivity. In an interior of a drift tube, air flow moving from a detector side to an ion source side is generated, and there are arranged, in order from an upstream side of the air flow to a downstream side thereof, a first region where a flow rate increases in a flow direction, a second region where the flow rate is constant, and a third region where the flow rate decreases. Light irradiation mechanisms for dissociating an ion are provided in the second region.