Spectrophotometric determination of bromide in water using the multisyringe flow injection analysis technique coupled to a gas-diffusion unit

A novel spectrophotometric method for the determination of bromide has been developed using the Multisyringe Flow Injection Analysis technique (MSFIA). This method is based on the decolorization of methylene blue by the bromine released from the oxidation of bromide by bromate under acidic conditions. By incorporating a gas-diffusion unit into the MSFIA system the transferred bromine reacts with methylene blue in the acceptor stream. The decrease of the methylene blue absorbance is monitored at 745 nm. The oxidation conditions are not strong enough to oxidize chloride to chlorine, which is a major component of both natural and seawater. The proposed method provides linearity for the determination of bromide over a range of 1 × 10^-5 mol L^-1 to 6 × 10^-5 mol L^-1 in 5 × 10^-2 mol L^-1 of chloride, with a correlation coefficient (r²) of 0.9939, and a precision of 3.1% (%RSD for 3 × 10^-5 mol L^-1 Br^- in 5 × 10^-2 mol L^-1 Cl^-, n = 10). The limit of detection (3σ) is 0.5 × 10^-5 mol L^-1. The proposed method has been applied to the determination of Br^- in water samples, obtaining recoveries in the analysis of spiked tap, natural, and seawater samples in the range of 90-106%.