A spectrophotometric method for determination of phosgene in air

A reagent consisting of 0.4% of nitrobenzyl pyridine and 0.5% of sodium acetate in ethanol was found to be applicable as a sampling and coloring solution to a sensitive and relatively specific spectrophotometric determination of phosgene. This method is a modification of the method developed by Noweir et al. An aqueous 0.005% methyl orange pretrap was used to eliminate interference with chlorine and hydrogen chloride which are likely to be encountered in industrial environment. This colour produced by this method was stable for 2 hours, reduced by 3% and 7% after 3 and 4 hours of sampling respectively. The method is so sensitive as to detect phosgene at a concentration of 0.1 microgram/ml in the sampling solution with the coefficient of variation (CV) of 4.5%. The collection efficiency of phosgene with the sampling solution was found to be greater than 98% at a sampling rate of 1 l/min.