Nitrogen Oxide Gas Sensor Based on a Nitrite-Selective Electrode

Incorporation of dicyanocobalt(III) a,b,c,d,e,f,g-heptapropylcobyrinete in plasticized poly(vinyl chloride) membranes has resulted in the development of electrodes that are selective for nitrite. An NO_x gas sensor was prepared by placing this electrode behind a microporous gas-permeable membrane. NO_x is generated in the sample at pH 1.7 and, after crossing the gas-permeable membrane, is trapped as nitrite by an internal solution buffered at pH ≥ 5.5. This sensor is different from the conventional Severlnghaus-type sensor, which employs a flat-bottom pH electrode. The latter senses changes in the pH of an internal unbuffered solution as NO_x diffuses across the gas-permeable membrane. The Severinghaus-type sensor exhibits severe interferences from weak lipophilic acids that can cross the gas-permeable membrane and affect the pH of the internal solution. The described NO_x sensor does not suffer from such interferences and exhibits better detection limits.