NMR and MS analysis of 15N-labelled complex mixtures: investigation of chloramine disinfection by-products Justinas Sakas, Maria Vorka and Dušan Uhrín University of Edinburgh, UK
Chloramination is a water disinfection method used around the world to provide potable water. The addition of chloramine (NH 2 Cl) kills pathogens, however it also reacts with naturally dissolved organic matter (DOM) and anthropogenic contaminants to produce a complex mixture of disinfection by-products (DBPs), which are known to be cytotoxic, genotoxic and carcinogenic. 1 Although the level of some of these compounds is regulated, the majority of by-products are unregulated and more than 70% of chloramination DBPs are unknown. 2 Additionally, it has been shown that the total toxicity of DBPs cannot be accounted by regulated compounds alone. 3 Therefore, it is necessary to elucidate the structures of all DBPs in order to find out if they pose any health risks. Unfortunately, the structure elucidation of complex mixtures is an arduous task as they contain hundreds or even thousands of compounds that cannot be easily separated using chromatographic techniques. Fourier- transform ion cyclotron resonance mass spectrometry (MS) offers extremely high sensitivity and resolution and thus can be used for untargeted analysis of complex mixtures, bypassing the customary chromatographic step. To complement the information obtained from mass spectra, nuclear magnetic resonance (NMR) spectroscopy can be used to provide detailed structural information. NMR analysis of complex mixtures can be simplified by targeting specific moieties present in a subset of molecules in order to achieve spectroscopic ‘separation’. Recent examples include structure elucidation using NMR experiments designed for compounds tagged with −O 13 CH 3 and fluorinated compounds. 4,5 In this work, we have implemented new MS formula assignment procedures using the CoreMS Python library 6 for compounds containing halogens and 15 N atoms without the need for comparison to unlabelled data. Information about the reaction types occurring during chloramination is extracted from the detected molecular formulae using various statistical techniques, including the PageRank algorithm (also used by Google to rank search results). 7 Finally, new NMR experiments were designed to aid structure elucidation of 15 N-containing DBPs, such 1 H, 15 N constant-time HMQC-COSY in which proton-proton correlations are obtained between adjacent CH and 15 NH groups. We believe this suite of new methods will be applicable to other fields analysing 15 N-labelled mixtures, such as metabolomics. References 1. X. Li and W. A. Mitch, Environ. Sci. Technol. , 2018, 52 , 1681–1689. 2. G. Hua and D. A. Reckhow, Water Res. , 2007, 41 , 645–651. 3. R. Mian, G. Hu, K. Hewage, M. J. Rodriguez and R. Sadiq, Water Res. , 2018, 147 , 112–131. 4. N. G. A. Bell, A. A. L. Michalchuk, J. W. T. Blackburn, M. C. Graham and D. Uhrín, Angew. Chem. Int. Ed. , 2015, 54 , 8382–8385. 5. A. J. R. Smith, R. York, D. Uhrín and N. G. A. Bell, Chem. Sci. , 2022, 13 , 3766–3774. 6. Y. E. Corilo, W. R. Kew and L. McCue, EMSL-Computing/CoreMS: CoreMS 1.0.0, 2021. 7. Zenodo. DOI: 10.5281/zenodo. 4641553.L. Page, S. Brin, R. Motwani and T. Winograd, The PageRank Citation Ranking: Bringing Order to the Web , The Web Conference, 1998.
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