Spectrophotometric determination of nitrite by its catalytic effect on the oxidation of congo red with bromate

A novel simple, sensitive and rapid kinetic-spectrophotometric method for the determination of trace amounts of nitrite is proposed. The method is based on its catalytic effect on the oxidation of congo red (CR) by potassium bromate in acidic solution. The oxidation reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of CR at a suitable λmax= 570 nm for the first 10–40 s from the start of the reaction. Under the optimum experimental conditions (sulfuric acid, 0.3 M; CR, 0.75x10-4 M; potassium bromate, 5x10-4 M and 25 oC), nitrite can be determined in the range of 0.015–0.75 μg mL 1 with the detection limit of 0.006 μg mL 1. The relative standard deviation of five replicate determination of 0.25 μg mL 1 nitrite was 2.5%. The proposed method was applied satisfactorily to the determination of nitrite in spiked drinking water samples. KEY WORDS: Nitrite, Catalytic effect, Congo red, Spectrophotometry, Drinking water Bull. Chem. Soc. Ethiop. 2012, 26(2), 159-169. DOI: http://dx.doi.org/10.4314/bcse.v26i2.1