Spectrophotometric Determination of Nitrogen Oxides in the Air with 2-N-Ethyl-5-Naphthol-7-Sulfonic Acid

For the determination of nitrogen oxides in the air, the structure of diazo and coupling compounds was studied and tested by experiments. The conditions and methods of diazo and coupling reactions were investigated. Furthermore, a spectrophotometric method using sulfanilamide as a diazo compound and 2-N-ethyl-5-naphthol-7-sulfonic acid (N-ethyl J acid) as a coupling compound was proposed. The maximum absorption wavelength of sulfanilamide-Nethyl J acid azo compound was at 478 nm. The molar absorptivity was 4.31 × 104 L/(mol × cm) with a recovery of 98.7–100.9% and RSD of 1.85%. For nitrogen oxides, the determinate limit of this measurement was 0.015 mg/m3 and the determinate range 0.024–2.0 mg/m3. Moreover, a high degree of correlation was observed between the results obtained by the proposed method and the standard methods. The proposed method can be easily applied to determine nitrogen oxides in the air.