The determination of bromide has received increased interest in a variety of fields, but the bromide found in many natural samples occurs often at fairly low concentrations of µg l -1 level. We have reported a kineticspectrophotometric method for the determination of trace amounts of bromide based on its catalytic effect on the tetrabase-Chloramine T reaction. 1 This method is highly sensitive, but the catalyzed reaction proceeds so rapidly as to complete in 30 s at 20˚C. Hence, in order to follow the reaction, an elaborate procedure is required and a home-made device for in-cell mixing is used.Flow injection analysis is widely used as a simple and convenient approach to rapid analyses, in which the reaction time can easily be controlled by varying the flow rate of the solution and the length of reaction coil. Hence the application of a flow injection technique to the above-mentioned catalytic method based on a rather rapid reaction should offer a reproducible and rather convenient procedure for routine determinations of trace concentrations of bromide. Although some FIA methods for the determination of bromide have been reported [2][3][4][5][6][7] , these methods were not sensitive enough to determine bromide in µg l -1 level. The present paper describes an investigation regarding the adaptation of the tetrabase-Chloramine T method for the determination of bromide to a flow injection system. The effects of reaction variables, particularly pH, were examined in greater detail. It was observed that the use of acetate buffer of higher concentration, which leads the reaction solution to higher ionic strength, alleviates interferences of several ions. The resulting method is more sensitive, more reproducible and suffers less interference, yet has higher sample throughput, than the batch procedure:1 by the proposed method, as low as 1 µg l -1 of bromide can be determined with the relative standard deviation of 6.4 or 8.7%, while the detection limit of the batch procedure was 2 µg l -1 , at which the relative standard deviation was 17.1%. This method has been successfully applied to the determination of bromide in natural water samples. ExperimentalReagents Pure water was prepared by purifying distilled water with a Millipore Milli-Q SP system just before use. Reagent-grade chemicals were used throughout. A potassium bromide stock solution (0.1 M) was standardized by a Volhard titration. The working solutions were prepared by diluting this solution with water. A potassium iodide stock solution (0.1 M) was also standardized by Volhard titration. The working solutions were prepared by diluting this solution with water. An acetate buffer solution (pH 3.8) was prepared by mixing 176 ml of 2.0 M acetic acid and 19 ml of 2.0 M A flow injection analysis method is proposed for the spectrophotometric determination of trace amounts of bromide based on its catalytic effect on the oxidation of 4,4′-bis(dimethylamino)diphenylmethane (tetrabase) by Chloramine T in a weakly acidic solution. The effects of the reagent concentrations a...