On-line flow injection monitoring of ammonia in industrial liquid effluents

A flow-injection method was applied to on-line analysis for ammonia in industrial liquid effluents. The method utilised the diffusion of gaseous ammonia from an alkaline sample stream, through a microporous membrane, into a bromothymol blue indicator stream, with the resulting colour change measured photometrically using a red LED. Following initial development work, the method was adapted to an automated, portable system, which was capable of linear response in the range 1–100 mg 1−1 NH3-N. The portable flow injection monitor was powered by an external 12 V battery, and performed two-point self-calibration during each analytical cycle. The monitor was capable of unattended, continuous on-line monitoring of effluent streams at two industrial sites over several days. The results obtained were in good agreement with those produced by an indophenol blue laboratory reference method.