Specific Gas Probes:

Membranes are also used in specific gas probes for measuring dissolved gases and gas phase partial pressures. The specific gas analysis is based on the electrochemical oxidation or reduction of the gas at the suitable electrode of an electrochemical cell giving increase to a current whose magnitude depends on the concentration of the gas consumed in the electrochemical reaction. The overall detection system is protected through the membrane that is permeable to the particular gas component of interest. A membrane could be polytetrafluoro ethylene, polyethylene, polypropylene, nylon or cellophane. The membranes typically have pore sizes of several microns. Portable devices for specific gas analysis are available for detection of gaseous oxygen, carbon dioxide, sulphur dioxide,  hydrogen sulphide, nitrogen dioxide and hydrogen cyanide.