A device for determining a concentration of at least one gas in a sample gas flow by infrared absorption spectroscopy. The device includes an infrared radiation source which emits a radiation which is conducted through an analysis cell, a feed line, the sample gas flow which is conducted into and out of the analysis cell via the feed line, a detector which measures an absorption spectrum arising in the analysis cell, a suction jet pump which includes a propellant gas connection, and a propellant gas line which extends to the propellant gas connection of the suction jet pump. The suction jet pump is arranged downstream of the analysis cell and feeds the sample gas flow through the analysis cell via the feed line. The propellant gas line includes a regulating valve which regulates a propellant pressure in the propellant gas line.