An analyzer (100) and a process for analyzing a gas (G) for a predetermined substance. A sensor measures an indicator of the amount or concentration of the substance in a gas sample located in a measurement chamber (3). A movement of an actuating unit (4, 17, 19) in a first direction (R.1) increases the volume of a suction chamber unit (5). A movement of the actuating unit (4, 17, 19) in a second direction (R.2) decreases the volume of the suction chamber unit (5). A motor (7) rotates a cam disk (1) about an axis (MA). The actuating unit (4, 17, 19) is mechanically coupled to the cam disk (1). Each rotational position of the cam disk (1) relative to the axis (MA) determines a position of the actuation unit (4, 17, 19) and thus a volume of the suction chamber unit (5).