Optical sensor for ammonia based on the inner filter effect of fluorescence.

A new indicator-immobilization technique for the development of a sensor material for monitoring ammonia gas in aqueous solutions in presented. It is based on the change in absorbance intensity of a lipophilized pH indicator homogeneously dissolved in silicone rubber. Exposure to ammonia leads to a deprotonation of the indicator and this increases the absorbance of the base form of the indicator bromophenol blue. The sensor responds over a 17 μg/L to 17 mg/L concentration range, with a detection limit of 12 μg/L.