Spectrophotometric determination of trace bromide by its catalytic effect on the tetrabase-chloramine T reaction

A catalytic Spectrophotometric method for the determination of trace amounts of bromide is proposed. In acidic solution 4,4′-bis(dimethylamino)diphenylmethane (tetrabase) is oxidized by chloramine T to form a blue compound, which is further oxidized to a greenish-yellow compound. The reaction is accelerated by trace amounts of bromide and can be followed by measuring the increase in the absorbance at 600 nm; the maximum absorbance is obtained on an absorbance-time curve at a given reaction time. Since the maximum value increases with increase in bromide concentration, this value is used as the measured parameter for the bromide determination. Under the optimum experimental conditions (4.1 × 10−6 M tetrabase, 3.8 × 10−4 M chloramine T, pH 3.8, 20 °C), bromide can be determined in the range 2–100 μg l−1. The relative standard deviations (n = 10) are 0.9, 1.7, 3.7% for 60, 20 and 10 μg l−1 bromide, respectively. This method was successfully applied to a determination of bromide in natural water samples.