Study on Transformation of Natural Organic Matter in Source Water during Chlorination and Its Chlorinated Products using Ultrahigh Resolution Mass Spectrometry

Haifeng Zhang,^† Yahe Zhang,^‡ Quan Shi,^‡ Jianying Hu,^§ Mengqiao Chu,^† Jianwei Yu,^† and Min Yang^*,†

^†State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

^‡State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China

^§College of Environmental Science, Peking University, Beijing 100871, China

^*Corresponding Author: Tel: +86-10-62923475; fax: +86-10-62923541; e-mail: yangmin@rcees.ac.cn.

DOI: 10.1021/es203587q

Keywords: Chlorine; Halogenation; Molecules; Natural Organic Matter; Nitrogen

Abstract: Natural organic matter (NOM) can affect the performance of water treatment processes, and serves as a main precursor for the formation of disinfection byproduct (DBPs) during chlorination. To minimize such undesirable effects, a better understanding of its structural information and reactivity toward chlorine is necessary. In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was used to study the molecular composition of NOM in source water. More than four thousand NOM components were resolved in the sample. NOM molecules with a low degree of oxidation (low O/C ratio) were found to be more reactive toward chlorine than those with high O/C ratio. Totally, 659 one-chlorine containing products and 348 two-chlorine containing products were detected in the chlorinated sample at a high confidence level. The chlorinated products can be arranged into series, which indicate they were originated from precursor compounds in series related by the replacement of CH4 against oxygen. Of the 1007 chlorine-containing products observed in this study, only 7 molecular formulas can be found in previous studies, showing the distinct difference from previous studies. This study explored the reactivity of NOM toward chlorine on a molecular level, which was previously explained on the level of whole mixtures or fractions of NOM, and the identified chlorinated products may contribute to our knowledge of the unknown total organic halide (TOX).