A novel method for measuring dissolved gases in liquids

In many chemical and biotechnological plants, such as biogas plants, the measurement of the concentrations of dissolved gases and volatile components in liquids is very helpful for process control and to indicate and prevent process instabilities. Conventional membrane-covered electrochemical sensors are often not suitable for this purpose. Here we describe a new method for parallel measuring dissolved gases in complex and even corrosive liquids providing excellent selectivity, sensitivity, high long-term stability and low maintenance. The measuring method is an innovative combination of gas stripping and chemical sensing. It consists in the sequence of the following three main steps: (1) membrane-free extraction of the dissolved components in a special vessel by means of an extraction gas stream, (2) chromatographic separation of the gas mixture and (3) detection of oxidizable and reducible components by means of a coulometrically operated high-temperature solid-electrolyte cell. In the extraction vessel the dissolved volatile constituents pass off by diffusion via the open interface from the sample medium into an extraction gas stream that is passed through the vessel.