Basic principle of ion mobility spectrometry (IMS)
The principle of ion mobility spectrometry is based on the fact that ions generated under normal pressure drift in an electric field against the direction of flow of a gas. Ions of different mass and/or structure reach different drift velocities and are separated from each other until they hit a detector one after the other in time. The ratio of the ion velocities (v) to the strength of the electric field (E) is referred to as ion mobility and the separation of these ions over a certain distance based on the different drift velocities is referred to ion mobility spectrometry.
The setup of an IMS drift tube and the measurement procedure is shown in the following picture gallery. The drift tube consists of an ionization region and a drift region, which are separated by an ion shutter. The ions generated in the ionization region reach an ion shutter, which lets a small part of the ions into the drift region at certain times. Due to the electric field, the ions with different mass and/or structure reach drift velocities differing from each other and are thus registered by the detector at different times.