Organic and inorganic N-chloramines are converted to highly fluorescent dansyl derivatives by reaction with 5-dimethylaminonaphthalene-1-sulfinic acid (DANSO2H). The synthesis and properties of the sulfinic acid are described in detail. Details of the method for derivatizing dilute aqueous solutions of N-chloramines are given along with the application of HPLC to the separation of mixtures of chloramine derivatives. The derivatization method is applied to the analysis of aqueous solutions of individual amines and a mixture 2 mg/L as N in each amine component chlorinated to different Cl2/N levels and incubated for one hour. The chloramine concentrations measured in the manner are correlated with residual chlorine levels determined by the DPD-titrimetric method. A sample of a chlorinated surface water which contained high concentrations of dissolved organic nitrogen was analyzed and found to contain both organic and inorganic N-chloramines. The kinetics and mechanism of the derivatization reaction are discussed. (Copyright (c) 1984 American Chemical Society.)