Mass Spectrometry Identification of N-Chlorinated Dipeptides in

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Mass Spectrometry Identification of Nchlorinated Dipeptides in Drinking Water Guang Huang, Ping Jiang, and Xing-Fang Li Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b00228 • Publication Date (Web): 01 Mar 2017 Downloaded from http://pubs.acs.org on March 10, 2017

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Analytical Chemistry

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Mass Spectrometry Identification of N-chlorinated Dipeptides in Drinking Water

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Guang Huang, Ping Jiang, and Xing-Fang Li

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Division of Analytical and Environmental Toxicology, Department of Laboratory

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Medicine and Pathology, Faculty of Medicine and Dentistry, University of Alberta

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Edmonton, AB Canada T6G 2G3

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Corresponding author: Xing-Fang Li, [email protected], 1-780-492-5094

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Analytical Chemistry

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Abstract

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We report the identification of N-chlorinated dipeptides as chlorination products in

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drinking water using complementary high resolution quadrupole time-of-flight

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(QTOF) and quadrupole ion-trap mass spectrometry techniques. First, three model

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dipeptides,

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phenylalanylglycine (Phe-Gly), reacted with sodium hypochlorite, and these reaction

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solutions were analyzed by QTOF. N-Cl-Tyr-Gly, N,N-di-Cl-Tyr-Gly, N-Cl-Phe-Gly,

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N,N-di-Cl-Phe-Gly, N-Cl-Tyr-Ala, and N,N-di-Cl-Tyr-Ala were identified as the

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major products based on accurate masses,

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spectra. These identified N-chlorinated dipeptides were synthesized and found to be

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stable in water over 10 days except N,N-di-Cl-Phe-Gly. To enable sensitive detection

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of N-chlorinated dipeptides in authentic water, we developed a high-performance

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liquid chromatography–tandem mass spectrometry (HPLC-MS/MS) method with

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multiple reaction monitoring (MRM) mode. N-Cl-Tyr-Gly, N,N-di-Cl-Tyr-Gly,

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N-Cl-Phe-Gly, N-Cl-Tyr-Ala, and N,N-di-Cl-Tyr-Ala along with their corresponding

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dipeptides were detected in authentic tap water samples. The dipeptides were clearly

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detected in the raw water but the N-chlorinated dipeptides were at background levels.

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These results suggest that the N-chlorinated dipeptides are produced by chlorination.

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This study has identified N-chlorinated dipeptides as new disinfection byproducts in

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drinking water. The strategy developed in this study can be used to identify

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chlorination products of other peptides in drinking water.

tyrosylglycine

(Tyr-Gly),

tyrosylalanine

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(Tyr-Ala),

and

Cl/37Cl isotopic patterns, and MS/MS

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Analytical Chemistry

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Introduction

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Disinfection of drinking water is the most effective action to prevent waterborne

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diseases.1 However, natural organic matter and contaminants in source water

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unavoidably react with disinfectants (e.g., chlorine and chloramines) resulting in the

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formation of a large number of disinfection byproducts (DBPs), although only a few

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DBPs (e.g., trihalomethanes and haloacetic acids) are regulated.2,3 Epidemiological

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studies show an association of consumption of chlorinated drinking water with

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increased risk of bladder cancer.4-6 The regulated DBPs are the most abundant and

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easy to measure. However, none of these regulated DBPs has sufficient carcinogenic

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potency to account for the cancer risk observed in epidemiological studies.7,8 The

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majority (~70 %) of halogenated DBPs remain unidentified.9 We hypothesize that

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some of the unidentified DBPs may be of toxicological relevance.

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Proteins, peptides, and amino acids are relatively abundant with a median

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concentration of dissolved organic nitrogen (DON) of 0.37 mg/L as N in surface

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water.10 The majority of nitrogenous compounds