Breakpoint chemistry and volatile byproduct formation resulting from chlorination of model organic-N compounds

Aqueous solutions containing six model organic-N compounds (glycine, cystei ne, asparagine, uracil, cytosine, and guanine) were subjected to chlorinati on at various chlorine (Cl)to precursor (P) molar ratios for 30 min. Chlori ne residuals were determined by both DPD/FAS titration and the MIMS (Membra ne Introduction Mass Spectrometry) method to evaluate breakpoint chlorinati on behavior, residual chlorine distributions, and byproducts. DPD/FAS titra tion was found to yield false-positive measurements of inorganic combined c hlorine residuals in all cases. The breakpoint chlorination curve shape was strongly influenced by the structure of the model compound. Cyanogen chlor ide was found to be present as a byproduct in all cases, and the yield was strongly dependent on the CI:P molar ratio and the structure of the compoun ds, with glycine being the most efficient CNCI precursor. Six byproducts ot her than cyanogen chloride were also identified. Free chlorine measurements by DPD/FAS titration and MIMS were in good agreement. This finding, togeth er with the results of previously conducted research, suggests that both me thods are capable of yielding accurate measurements of free chlorine concen tration, even in solutions that contain complex mixtures of +1-valent chlor ine compounds.