Photometric determination of nitrite

A sensitive colored reaction for nitrite determination is developed. It involves the reaction of the titled ion with p-aminobenzoic acid to form a diazonium ion, which is then coupled with α-naphthol in alkaline medium to form a pinkish red soluble azo dye absorbing maximum at 519 nm. The described method is capable of determining 0.1–1.3 ppm of nitrite with a relative standard deviation of 0.3–1.7% depending on the concentration level, molar absorptivity of 3.5 × 10⁴ liter mol⁻¹ cm⁻¹, and Sandell sensitivity index of 0.0013 μg cm⁻². Diazotization and coupling are very fast and control of temperature is unnecessary. Moreover, the colored azo dye is stable and its intensity is in direct proportion with nitrite concentration over a wide range.