Repetitive determination of chloride using the circulation of the reagent solution in closed flow-through system

The precipitation reaction of silver chloride (AgCl) is carried out in a large amount of ammonia (NH₃). This makes possible to adopt a closed-loop flow injection (FI) system and to determine chloride repetitively. A solution of 30 mmol l^?1 silver nitrate and 80 mmol l^?1 NH₃ in a single reservoir (250 ml) is continuously circulated through the flow cell at a flow rate of 2.0 ml ml^?1. The chloride containing sample (100 μl) was introduced into this reagent solution by means of six-way valve. AgCl precipitates formed in the sample zone are monitored spectrophotometrically (at 500 nm) in the flow system. After passing through the flow cell, the excess NH₃ in the circulating reagent solution dissolves AgCl precipitates and the stream then returns to the reservoir. Various variables of the FI system were optimized and a study of interfering ions was also carried out. A linear calibration graph was obtained from 3.0 to 30 mg l^?1 chloride. Two hundred repetitive injections of 5.0 mg l^?1 chloride into the circulating reagent solution have shown unchanged base-line and good reproducibility. The method was successfully applied to the determination of chloride in tap, natural and the reference waters.