Flow Injection-Spectrophotometric Determination of Trace Amounts of Bromide by Its Catalytic Effect on the 4,4′-Bis(dimethylamino)diphenylmethane-Chloramine T Reaction

Abstract

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 are studied at two pH values: 3.2 adjusted with sulfuric acid and 3.8 with acetate buffer. Although the sensitivity is slightly lower and the background noise is larger at pH 3.8, several ions show less interference at pH 3.8 than at pH 3.2. The detection limit is 1 µg l^-1 and the calibration graph for bromide is linear up to 40 µg l^-1, showing a slightly negative deviation in the higher concentration range. The relative standard deviations for 1.0, 10.0 and 40.0 µg l^-1 of bromide are 6.4, 0.79 and 0.45%, respectively, at pH 3.2 and 8.7, 1.2 and 0.38%, respectively, at pH 3.8. Bromide in water samples can be determined at a sampling rate of 100 h^-1 with 300 µl sample injections. The procedure is applied successfully to the determination of bromide in natural waters.