MS and NMR analysis of isotopically-labelled chloramination disinfection by-products

FT-ICR MS and NMR analysis of an isotopically-labelled complex mixture of water disinfection by-products formed by chloramine disinfection of model phenolic acids is described. A new molecular formula assignment procedure using the CoreMS Python library able to assign isotopically-enriched formulae is proposed. Statistical analysis of the assigned formulae showed that the number of compounds, the diversity of the mixture and the chlorine count increase during the chloramination reaction. The complex reaction mixture was investigated as a network of reactions using PageRank and Reverse PageRank algorithms. Independent of the MS signal intensities, the PageRank algorithm calculated the formulae with highest probability at convergence of the reaction; these were chlorinated and nitrated derivatives of the starting materials. The Reverse PageRank revealed that the most probable chemical transformations in the complex mixture were chlorination and decarboxylation. This agreed with the data obtained from INADEQUATE NMR spectra and literature data, indicating that the above approach could be applied to gain insight into reactions pathways taking place in complex mixtures without any prior knowledge.