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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
