Detection of nitrobenzene and related aromatics by reduction and indophenol formation

The detection of nitrobenzene is based on its partial reduction with zinc in slightly acidic medium to yield phenylhydroxylamine, acid-catalyzed rearrangement to form a mixture of 2- and 4-aminophenol, and formation of indophenol blue by 4-aminophenol on oxidative coupling with an alkaline phenol solution. The limit of detection is 0.1 μg ml^?1 nitrobenzene in the test solution. A positive test is also given by 2- and 3-nitrotoluene but various other aromatics containing nitro groups do not interfere. The method was tested on wastewaters.