Aportable,12Vbattery-powered,automatedspectrophotometric field monitor has been developed that permits the continuous long-term recording of the total ammonia concentration in the surrounding aquatic environment. The flow-injection (FI)-based monitor incorporates a gas diffusion unit and an acceptor stream containing an acid-base indicator. The detection system utilizes a red solid-state light-emitting diode source and photodiode detector. Remote control and data processing are achieved by an inhouse-designed microcomputer system. The instrumentation was fully evaluated in the laboratory and was shown to operate unattended for periods of up to 1 week (analyzing every hour) before battery charging and reagent replacement were required. The precision and accuracy of the chemical monitor was examined by continuously analyzing a sample of a known ammonia concentration (80.0 mg L โซ1ืโฌ NH 3 -N) at 60 minute intervals over a 7 day period (n โซืกโฌ 170). The calculated mean concentration was 79.0 mg L โซ1ืโฌ (using 50 and 150 mg L โซ1ืโฌ standards) with an RSD of 5.2%. The detection limit (3r) was determined as 2.5 mg L โซ1ืโฌ . The feasibility of using the system in situ was demonstrated by a 2 week field trial in which the automated field monitor was successfully deployed at a landfill leachate lagoon. Data from the trial are presented, and the potential applications of the system in environmental management are discussed. แญง 1997