Abstract

Optical sensing films for ammonia gas have been developed by immobilizing zinc 5,10,15,20-tetraphenylporphine (ZnTPP) in silicone rubber. The detection of ammonia can be achieved using both absorbance and fluorescence emission measurements. Spectral changes were observed due to the coordination of NH3 molecules to the ZnII ion in the immobilized metalloporphyrin. Effects of other immobilization matrices on sensor properties were investigated. ZnTPP-silicone films were found to show a reasonably high sensitivity to ammonia, with a linear range of 0-6 mg m-3 (0-8.5 ppm). The detection limit for ammonia in nitrogen was 0.5 mg m-3 (0.7 ppm). The equilibrium response time of the films was approximately 4 min and the reaction with ammonia was reversible. ZnTPP films were also found to be sensitive to triethylamine.