A simple, sensitive, and selective method for rapid determination of nitrite is described which is based on its catalytic effect in the reaction between thymol blue and bromate in acidic media. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance at 543 nm by a fixed time method of 2.0 min. The method allows the determination of nitrite in the range 0.4-1500 ng/ml. The relative standard deviation for seven determinations of 40 ng ml 01 nitrite is 1.54% and the detection limit of the method is 0.32 ng ml 01 . The method is applied to the determination of nitrite in water. แญง 1997 Academic Press The important role of nitrite in producing N-nitrosamines, some of which have been shown to be carcinogens in the human body, is well established (1). The occurrence of nitrite salts in the environment and their use as food preservatives is widespread. The level of organic pollution in water is indicated by nitrite (2). Hence rapid, sensitive, and accurate methods are required for determination of ultratrace amounts of nitrite in different samples. The method most commonly used to determine trace levels of nitrite is based on the spectrophotometric measurement of the azo dye formed by diazotization of an aromatic amine by nitrite followed by coupling of the diazonium cation with an aromatic amine or phenol (3-8). These methods are time consuming and the reagents used are toxic.
Catalytic kinetic methods are an attractive alternative for the determination of ultratrace concentrations of nitrite. Such methods have the general advantages of combining high sensitivity with relatively simple procedures and apparatus. Some methods for the determination of nitrite based on its catalytic effect have been reported (9-14). Most of these methods lack sufficient sensitivity for determinations at or below ng ml 01 levels, and, therefore, more sensitive and selective methods are required.
This paper describes a rapid, accurate, sensitive, and selective method for the determination of nitrite based on the catalysis of the reaction of thymol blue with bromate in acidic media. The detection limit of the method is 0.32 ng/ml.
EXPERIMENTAL
Reagents
Triply distilled water and analytical-reagent grade chemicals were used. A 1000 mg/liter nitrite stock solution was prepared by dissolving 1.500 g sodium