Extraction–spectrophotometric determination of nitrite using 1-aminonaphthalene-2-sulphonic acid

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Abstract
A simple and highly sensitive extraction–spectrophotometric method for the determination of nitrite is described. The method is based on diazotization of o-nitroaniline with nitrite and subsequent coupling with 1-aminonaphthalene-2-sulphonic acid in acidic medium to yield a red dye with an absorption maximum at 545 nm. The dye could be extracted into isopentyl alcohol, whereupon its absorption maximum shifted to 530 nm. Beer's law is obeyed in the range 0.08–0.68 and 0.01–0.08 ppm of nitrite in the aqueous and extraction systems, respectively. The molar absorptivity and Sandell's sensitivity were found to be 5.46 × 104 dm3 mol–1 cm–1 and 0.0008 µg cm–2, and 4.83 × 105 dm3 mol–1 cm–1 and 0.00009 µg cm–2 in the aqueous and extraction systems, respectively. The method is free from the interferences of Cu and Fe which are the normal interferents in other methods. The method was applied successfully to the determination of nitrite in polluted water.