The composition of oxidant-reactive dissolved organic nitrogen (DON) is poorly characterized, although its ozonation is likely to form a great variety of disinfection by-products containing a nitrogen-oxygen bond (NDBPs). In this study, two chemical oxidation procedures were developed: continuous ozonation at pH 7.0 and free available chlorine (FAC) titrations at pH 9.2. The formation of two oxidation products (nitrate (NO3 ) and chloramines, respectively) was used to quantify and characterize oxidant-reactive nitrogenous moieties in DON. In addition, batch experiments were conducted to study the NO3 yields of 30 selected nitrogenous model compounds upon ozonation. The NO3 yields of 12 primary and secondary amines were highly variable (17-100%, specific ozone dose of 20 molO3/molN), 7 amino acids had high NO3 yields (>= 90%), and tertiary amines as well as pyrrole, acetamide and urea had low NO3 yields (<= 15%). The mechanisms of NO3 formation were further examined with benzylamine and N-methylbenzylamine as model compounds. Our results show that nitroalkanes are the last intermediate products before the formation of NO3 , both for primary and secondary amines. The presence of an electron-withdrawing group in the vicinity of the N-atom facilitates the formation of NO3 from nitroalkanes. Therefore, the formation of NO3 is attributed to amino acids and activated primary and secondary amines. In contrast, all primary and secondary amines were transformed to chloramines upon chlorination, which was determined by a novel oxidative titration with chlorine. To further support the selectivity of this assay, it was demonstrated by derivatization of amine moieties that chloramine formation could be inhibited. 13-45% of the DON of 4 dissolved organic matter isolates and 2 wastewater effluents formed NO3 and 0-39% formed chloramines, indicating that the potential for N-DBP formation is high (mu MN/mgC-level). From differences in the formation of NO3 and chloramines the nature of the precursors can be hypothesized (e.g., activated or nonactivated primary and secondary amines, partially oxidized nitrogenous compounds). This study highlights the capacity of two novel methods to characterize the oxidant-reactive DON fraction. Our results suggest that this fraction is significant and could form a variety of potentially toxic N-DBPs.