Spectrophotometric Method for the Determination of Nitrite and Nitrate

The diazotisable amine, p-aminoacetophenone has been diazotized with nitrite in the presence of hydrochloric acid at room temperature, and the diazotized salt thus produced has been allowed to couple with the reagent, 2,3-dihydroxynaphthalene in alkaline medium to produce a reddish orange azo-dye suitable for the determination of nitrite at ppm level. The ʎmax of the azo-dye being 475 nm. The very azo-dye is extractable into an organic solvent like ethylacetate without shifting the ʎmax. Similarly, nitrate ion forms a strong reddish-yellow nitro product with 2,3 dihydroxynaphthalene in the presence of concentrated sulfuric acid. This nitro product is extractable into ethylacetate, and its absorbance is measured at 380nm ( ʎmax ).The Beerˊs law for nitrite and nitrate were obeyed in the range, 0.1 to 5.0 ppm and 0.2 to 25 ppm, respectively. The molar absorptivity of nitrite and nitrate methods are 2.5х104 and 3.2х103 L.mol-1cm-1 respectively. The RSD for both the methods are in the range, 0.5 to 2.5%.