Spectrophotometric determination of nitrite in water

Abstract

A sensitive and selective colour reaction for the determination of nitrite is presented. Nitrite reacts with p-aminophenylmercaptoacetic acid in the presence of hydrochloric acid to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)ethylenediamine dihydrochloride in acidic medium to form a stable bluish violet azo dye. The method is suitable for the determination of nitrite from 0.02 to 0.80 p.p.m. in a 1.0-cm cuvette. The observed molar absorptivity and Sandell's sensitivity of the azo dye are 4.65 × 10⁴ l mol^–1 cm^–1 and 0.001 µg cm^–2, respectively. The method is free from most interferences. The method has been applied to polluted water samples and the results obtained compare favourably with those from standard methods.