Colorimetric Determination of 2-Chlorobenzylidene Malonitrile in Gases and Liquids

Here is described a new approach for the simple and rapid detection of 2-chlorobenzylidene malonitrile (CS riot control agent) based on the reaction with isatin (1H-indole-2,3-dione) and, alternatively, with ninhydrin (2,2-dihydroxy-1H-indene-1,3(2H)-dione), both in an environment of ammonium acetate, dimethyl sulfoxide, and dimethylformamide. The method was designed for the preparation of detection tubes for air analysis, test strips for the analysis of liquid samples, and for spectrophotometric determination. The use of ninhydrin appears to be more sensitive, but isatin provides higher stability and practical applicability.