Studies with solid-state phosphorescent coatings on their sensitivity to nitrogen oxides

Phosphorescent polymer film compositions and phosphorescent Langmuir-Blodgett coatings based on platinum and palladium porphyrins were tested in the presence of nitrogen oxides (NOx). Dynamic quenching of phosphorescence by NOx was observed. It was accompanied by chemical interaction of NOx with the dye molecules which caused persistent decrease of the phosphorescence signal and irreversible degradation of the sensor. Two modes of NOx quantitation based on measurement of either phosphorescence lifetime or time drift of intensity were examined. For the phosphorescent polymer film compositions the analytical range of NOx was found to be 0-3.0% (mm) with a detection limit of 0.1%. For the LB-film coatings the sensitivity for NOx was about five times better: the range was 0-1.0% (mm) with a detection limit of 0.02%. Although for both systems the analytical range of NOx covered was poor for practical purposes, the data obtained are useful for evaluation of possible interferences by NOx in other applications, such as in oxygen and SO2 sensors. The possibilities of the realization of a dual-sensing concept with a single phosphorescent probe is discussed with respect to simultaneous measurement of NOxoxygen using polymer film compositions and NOxSO2 using Langmuir-Blodgett coatings.