The invention relates to an ion mobility spectrometer in which a measuring
tube, a filter and a transport device are connected to form a circulatory
gas system, with a gas inlet which introduces ambient gas for analysis
into the measuring tube of the ion mobility spectrometer. The invention
involves connecting the measuring tube with the ambient gas by means of a
dosing channel and connecting the circulatory gas system with the ambient
gas by means of an outlet channel. The outlet channel joins the
circulatory gas system between the high-pressure side of the transport
device and the measuring tube, so that ambient gas for analysis is
introduced into the measuring tube via the dosing channel while, at the
same time, gas flows out of the circulatory gas system via the outlet
channel without further transport devices being required.