Kinetic spectrophotometric determination of trace amounts of nitrite by catalytic reaction between methylthymol blue and bromate

A kinetic spectrophotometric method for determination of trace nitrite in two dynamic ranges (2-100 and 100-500 ng/mL) based on its catalytic effect on the reaction between methylthymol blue and potassium bromate in acidic (sulfuric acid) media is described. The reaction was monitored spectrophotometrically by measuring the decreasing color of methylthymol blue at 437 nm by the fixed-time method of 4.0 min at 30 degreesC. The detection limit is 0.6 ng/mL, and the relative standard deviations for 50.0 and 250.0 ng/mL nitrite are 1.6% and 1.3%, respectively. The method was used for the determination of nitrite in water samples.