Determn. of nitrogen oxide(s) in gas mixts. - by oxidising, treating with hydrazine deriv. to form di:nitrophenyl azide followed by spectrophotometric determn. of azide

摘要

Process comprises oxidn. of lower N oxides to NO2/N2O4 mixts., e.g. with CrO3; then passing the gas stream through a reaction tube packed with excess 2,4-dinitrophenyl hydrazine or other chromogenic hydrazine on a solid inert carrier; chromatographic sepn., of the resulting dinitrophenyl azide; and spectrophotometric determn. of the azide. The process is also applicable to gas mixts. contg. NO2, N2O4, aldehydes (esp. HCHO) and ketones, as the carbonyl cpds. produce the corresp. hydrazones, which are sepd. from azide chromatographically and also determined spectrophotometrically. Amperometric or voltametric redn. of the nitro substits. is an alternative means of analysis. USE - Process detects down to 0.1 ppb N oxides and down to 0.01 ppb carbonyl cpds., e.g. in the analysis of car exhaust gases and gas fire environments.