Development of NOx gas sensors based on nitrate-selective polypyrrole electrodes

A nitrate-selective polypyrrole-based electrode was used in the development of NOx sensors. The nitrate-selective film was prepared by electropolymerizing pyrrole in presence of a nitrate salt. This resulted in a film that responded to nitrate in buffered media with near-Nernstian slopes and excellent reproducibility. This electrode was incorporated into a gas-sensing arrangement where it was immersed in a buffered compartment and separated from an acidified sample solution by a gas-permeable membrane. Additions of nitrite to the acidified solution resulted in the production of NOx, which can cross the gas-permeable membrane into the buffered internal filling solution where it is trapped as nitrate and sensed by the nitrate-selective polypyrrole electrode. This sensor arrangement resulted in detection limits in the mu M range and had excellent selectivity characteristics.