Spectrophotometric method for the determination of trace levels of nitrite in waters

Abstract

A selective and sensitive spectrophotometric method for the determination of nitrite is presented. It relies on the reaction of the nitrite with 4-amino-1-naphthalenesulphonic acid (naphthionic acid) to form a diazonium ion, which is coupled with 1-naphthol, in a basic medium, to form a stable water soluble purple azo dye anion, which shows an absorption maximum at 530 nm. Beer's law is obeyed in the range 3.3–98.6 µg of nitrite-nitrogen in a final volume of 20 ml, with a molar absorptivity of 30.5 × 10³ l mol^–1 cm^–1, sensitivity index of 0.0033 µg cm^–2, relative error of +0.24 to –1.0% and relative standard deviation of 0.2–4.0%, depending on the concentration level. Furthermore, the reaction is fast and temperature control is unnecessary.