Nitrogen-15 NMR study on the incorporation of nitrogen into aquatic NOM upon chloramination

Chloramination is being used increasingly in water treatment to lower the formation of regulated disinfection byproducts (DBPs). How monochloramine nitrogen becomes incorporated into aquatic natural organic matter (NOM) and potentially affects the formation of nitrogenous DBPs is an unresolved question in the chemistry of humic substances. To address the problem, Suwannee River NOM and Suwannee River fulvic acid were reacted with preformed ¹⁵NH₂Cl and analyzed by solid and liquid state ¹⁵N NMR spectrometry. Both samples were also reacted with ¹⁵NH₄Cl as a control. A majority of the monochloramine nitrogen incorporated into the samples matched the structural forms resulting from the control reaction with ammonia, indicating that condensation reactions of ammonia with the carbonyl functionality can partly explain the transformation of the ¹⁵NH₂Cl nitrogen into the NOM. These structural forms include aminohydroquinone, 1° amide, indole, and pyridine-like nitrogens. Spectra of the samples reacted with ¹⁵NH₂Cl also showed possible evidence for nitrosophenol nitrogens, which would arise from the reaction of hydroxylamine or nitrite, intermediates in the chemical oxidation of the inorganic nitrogen to nitrate.