Colorimetric Microdetermination of Nitrogen Dioxide in Atmosphere

The determination of nitrogen dioxide in the atmosphere has heretofore been hampered by difficulties in sample absorption and lack of specificity. A new specific reagent has been developed and demonstrated to absorb efficiently in a midget fritted bubbler at levels below 1 ppM. The reagent is a mixture of sulfanilic acid, N-(1-naphthyl)-ethylenediamine dihydrochloride, and acetic acid. A stable direct color is produced with a sensitivity of a few parts per billion for a 10-minute sample at 0.4 liter per minute. Ozone in five-fold excess and other gases in tenfold excess produce only slight interfering effects; these may be reduced further by means which are described. 25 references, 1 figure, 3 tables.