AMMONIA-SENSITIVE POLYMER MATRIX EMPLOYING IMMOBILIZED INDICATOR ION-PAIRS

A new sensor material for monitoring ammonia in aqueous solution is pr esented. It is based on lipophilic ion pairs consisting of an anionic pH indicator and a quaternary ammonium cation. The ion pairs are homog eneously distributed inside a layer of a silicone elastomer. Exposure of the indicators to ammonia leads to de-protonation of the hydroxy gr oup, and this causes the strong absorbance of the basic form of the in dicator. The process is fully reversible. The sensor can easily be man ufactured from plastic materials and responds to ammonia over the conc entration range of 0.015 to 20 mg l(-1) with a detection limit of 15 m u g l(-1), and is not affected by pH because the silicone matrix is pr oton-impermeable. The sensor is intended for use as a probe to monitor ammonia in surface waters.