The method ia applicable of oxide of nitrogen contents equal to or greater than 0, 00002 % (m/m). The principle is based on oxidation of nitrous nitrogen to nitric nitrogen by potassium permanganate. Reaction of nitric nitrogen with 2, 4-xylenol under specified conditions to form a nitrate derivate. Distillation of the nitrate derivate and absorption in sodium hydroxide solution. Spectrophotometric measurement of the yellow coloured nitrophenol at a wavelength of about 445 nm.