Diazo-coupling spectrophotometric determination of nitrogen oxides in the air

Özet

A new accurate, sensitive, rapid and convenient measurement for the determination of nitrogen oxides inthe air was established. After being oxidized by chromium trioxide (CrO3), nitrogen oxides in the airexisted in the form of NO2, then forming nitrite and nitrate after being absorbed by the alkaline aqueoussolution. Under acidic condition, the diazo reaction is specific to the nitrite and primary aromatic amine.In this paper, the structure of diazo and coupling compounds were selected and tested through theexperiments. The relationship between the azo compound's molecular structure and the sensitivity ofthe method as well as the electronic flow direction in the conjugated system of azo compounds werestudied. A theory that conjugated system's electron cloud in azo compound's molecule flowed fromcoupling compounds to diazo compounds through nitrogen and nitrogen double bond was proposed.This theory had a guiding function for exploiting highly sensitive chromogenic agents. Furthermore, theconditions and methods of diazo reaction and coupling chromogenic reaction were investigated. Aspectrophotometry that p-aminobenzenesulfonic acid as diazo compound and 2-amino-5-naphthol-7-sulfonic acid (J acid) as coupling compound for the determination of nitrogen oxides in the air wasestablished. The maximum absorption wavelength of p-aminobenzenesulfonic acid-J acid azo compoundwas at 480 nm. And the molar absorptivity was 4.01 104 L mol1 cm1 with recovery of 98.5%e100.9%and R.S.D. of 1.82%. In addition, the determination limit of measurement was 0.017 mg m3 nitrogenoxides and the determination range was 0.027e2.0 mg m3 nitrogen oxides. This method can be easilyapplied to the determination of the nitrogen oxides in the air