Optical ammonia sensing films based on an immobilized metalloporphyrin

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 Zn^II 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.