Abstract: An analyzer and a process analyze a breath sample exhaled by a subject for a predetermined substance, particularly alcohol. An input fluid connection connects an input unit (1) to a measuring chamber (3). A suction fluid connection connects the measuring chamber to a suction chamber unit (5, 6), that is selectively transferrable to a with minimum volume state or a maximum volume state. A sensor (12) measures an amount or a concentration of the substance in the measuring chamber. A drive unit (4, 11) moves a valve (2, 13) for the input fluid connection selectively into a closing or into a releasing end position. The drive unit can also move the suction chamber unit between the two states. The movement of the valve (2, 13) from one end position to the other end position is coupled with a transfer of the suction chamber unit (5, 6) between the two states.