Reaction rate method for determination of nitrite by applying a stopped-flow technique

A rapid, sensitive, and accurate method for the determination of nitrite is described based on its catalytic effect on the reaction between thymol blue and bromate in the presence of sulphuric acid. The optimum conditions for various parameters on which the rate of the reaction depends, such as temperature and pH, were investigated. The kinetics of the reaction were established by monitoring the decrease in absorbance of thymol blue at 543 nm by a stopped-flow technique. The linear calibration range for low concentration of nitrite ions was found to be 5-80 ng ml(-1)with a 2 sigma limit of detection of 4.5 ng ml(-1). The calibration for higher concentrations of nitrite was linear from 0.1 to 25 mu g ml(-1). The interference effect of several ions was investigated. The method can be extended to the determination of nitrate after their reduction to nitrite. (C) 1998 Elsevier Science B.V. All rights reserved.