Direct analysis of organic chloramines in low concentrations in aqueous solutions is achieved by membrane introduction mass spectrometry. Tandem mass spectrometry allows structures of the chlorination products to be determined and shows that nitrogen chlorination occurs for aliphatic amines and ring chlorination for aniline. Monochlorination of aniline occurs mainly at the ortho position, while dichlorination yields 20-35% diortho and 80-65% ortho-para substitution products. Depending on the reaction conditions, the actual chlorination reagent can be chloramine, hypochlorous acid, and possibly chlorine. The high ortho chlorination yields of aniline are explained by a mechanism in which chlorination occurs first at the nitrogen atom with subsequent intramolecular rearrangement to the ortho position in analogy to rearrangement of the nitro group in N-nitro aromatic amines. Using flow injection analysis procedures, it is possible to follow in an on-line fashion reactions that yield (or remove) organic chloramines at sub parts per million levels.