Catalytic Spectrophotometric Determination of Traces of Nitrite Based on the Oxidative Decoloration of Toluidine Blue by Potassium Bromate

It was found that in 1.5 mol·L-1 phosphoric acid medium,the redox reaticon between KBrO3 and Toluidine Blue (TB) was strongly catalyzed by NO-2 ion,leading to an enhancement of color-fading of the TB.Influential factors,including the kinds and concentration of acid mediums,amount of KBrO3 and TB added,temperatue and time of reaction,and interferences of coexisting ions were studied and optimized.Linear relationship between values of lgΔA(ΔA=A0-A) and mass concentration of NO-2 ion was obtained in the range of 0.01-0.12 mg·L-1 as measured at the absorption maximum of 622 nm.Detection limit (3s) of the method found was 4.8×10-7g·L-1.The proposed method was used in the determination of NO-2 ion in water sample,giving values of recovery ranged from 99.3% to 105.7%,and values of RSD′s (n=9) in the range of 2.5%-2.9%.