Abstract
A reagent consisting of 0.25% 4-p-nitrobenzylpyridine and 0.5% N-benzylaniline in diethylphthalate was tested and proved to be highly sensitive and relatively specific for the spectrophotometric determination of phosgene in air. Concentrations under 0.1 ppm of phosgene in air may be determined with reliability. The color developed with the reagent was stable for several hours and only slightly affected by normal ambient humidity. None of the following substances interfered with the reaction: hydrogen chloride, chlorine, chlorine dioxide, carbon tetrachloride, chloroform, trichloroethylene, tetrachlorethylene, and dichlorodifluoromethane in concentrations likely to be encountered under industrial conditions.