Abstract: Apparatus for determining the concentration of a component of a gaseous mixture by selective absorption of the component in a liquid absorbent and measurement of a property of the absorbent, such as the electrical conductivity, related to the concentration of the component therein, comprising an absorption cell for containing the liquid absorbent; means for bringing a stream of said gaseous mixture into contact with the absorbent; means for flushing the absorption cell with absorbent from a reservoir so as to recharge the cell with absorbent; and means for providing a first signal related to said property of the absorbent immediately after flushing the cell, for providing a second signal related to the property after a predetermined time, and for providing a third signal related to the difference between the second and first signals.