An efficient absorbing system for spectrophotometric determination of nitrogen dioxide

A simple and sensitive spectrophotometric method for determination of atmospheric nitrogen dioxide using o-nitroaniline as an efficient absorbing, as well as diazotizing, reagent is described. o-Nitroaniline present in the absorbing medium is diazotized by the absorbed nitrite ion to form diazonium compound. This is later coupled with 1-amino-2-naphthalene sulphonic acid (ANSA) in acidic medium to give red-violet-coloured dye,having λ_max = 545 nm. The isoamyl extract of the red azo dye has λ_max = 530 nm. The proposed reagents has ≈ 100% collection efficiency and the stoichiometric ratio of NO₂:NO₂^? is 0.74. The other important analytical parameters have been investigated. By employing solvent extraction the sensitivity of the reaction was increased and up to 0.03 mg m^?3 nitrogen dioxide could be estimated.