Spectrophotometric determination of low levels of bromate in drinking water after reaction with fuchsin

Abstract

A simple spectrophotometric procedure for the determination of trace levels of bromate in drinking water is described, which uses metabisulfite reduction to form bromine and reaction with reduced fuchsin to form a bromurated red coloured product absorbing at 530 nm. The present procedure is free of known interferences (Cl^–, ClO₃^–, SO₄^2–) which affect other commonly used analytical techniques, such as ion chromatography, and thus require time consuming steps for separation with additional costs. Cationic interferences from heavy metals and major elements are removed by passage through a strong cationic resin (Na⁺ form). The sample is then mixed with a little volume of fuchsin solution decoloured with excess of metabisulfite in HCl medium and 1–2 ml of citrate buffer solution (pH 3.4). Bromate is converted to bromine by metabisulfite and subsequently reacts with fuchsin regenerating the quinoide structure absorbing at 530 nm. Maximum colour development occurs at about 26 min after reagent addition and absorbance is stable for at least 30 min. The response is linear up to 20 µg l^–1 of bromate. The detection limit (propagation of errors approach) is 1 µg l^–1 (40 mm path length) and the precision (short term relative standard deviation) is 6% at 5 µg l^–1 level of bromate (n = 10). This method allows a low detection limit to be reached making it particularly attractive for accurate control of bromate level in drinking water in accordance to the European standard.