DNCB (2,4-dinitrochlorobenzene) is used in the treatment of alopecia areata, recalcitrant verrucae, and for evaluating immunocompromised patients. Currently, there is no pharmaceutical grade of DNCB available for clinical use. Recently, no nitrochlorobenzene contamination was found with the use of positive ion detection gas chromatography-mass spectrometry. We examined six commercial sources of DNCB, with the use of negative ion detection gas chromatography-mass spectrometry, for volatile impurities such as nitrochlorobenzene which might remain from the manufacturing process. The use of negative ion detection increases the sensitivity of this technic to benzene rings substituted with electron withdrawing groups like the nitrochlorobenzenes. We found that all sources of DNCB contain various combinations of nitrochlorobenzene, dinitrobenzene, nitrodichlorobenzene, and other isomers of DNCB. Nitrochlorobenzene has been shown to be mutagenic in the Ames test and carcinogenic in animal studies. The presence of nitrochlorobenzene and other contaminants in commercial grades of DNCB raises questions about the continued clinical application of this agent.
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