Studies On Disinfection By-Products Of Tryptophan In Chlorinated And Chloraminated Water

The safety of drinking water is the basic guarantee for the quality of human life.At present,chlorination or chloramination is mostly used to prevent the spread of water-borne diseases and ensure the safety of drinking water quality.Amino acids widely exist in water,and they will interact with disinfectants in the process of drinking water disinfection.In particular,aromatic amino acids are easy to react with disinfectants,such as electrophilic substitution and oxidation reactions,resulting in a large number of complex disinfection by-products(DBPs),which might be harmful to human health.Therefore,it is of great significance to study the DBPs produced by aromatic amino acids.In this paper,the DBPs generated from tryptophan,an aromatic amino acid,as the precursor during the chlorination and chloramination disinfection process of drinking water were studied using ultra performance liquid chromatography couple with quadrupole tandem time of flight mass spectrometry(UHPLC-Q-TOF HRMS).Furthermore,the reaction kinetics of tryptophan chloramination disinfection was studied as well by means of ultra high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry(UHPLC-QQQ MS).Firstly,a method for the analysis of the disinfecting reaction solution of tryptophan by UHPLC-Q-TOF HRMS was established.Fifteen chlorinated DBPs were found under the optimized instrument conditions.The structure of each DBPs was further inferred by accurate molecular weight and MSMS fragments.These chlorinated DBPs were aldehydes,alcohols,2-keto indoles,chlorides,dihydroxy substituted tryptophan and etc,which all contained the typical structural unit of indole ring from the tryptophan side chain in their structure.Based on the structural determining of the chlorination DBPs of tryptophan,the changing trend of their content against time in the disinfection reaction system with different molar ratios of tryptophan and sodium hypochlorite was further studied.Secondly,under the same UHPLC-Q-TOF HRMS analysis conditions,the structures of 16 chloramination DBPs of tryptophan were found and their structures were inferred by the similar method.They were amides,aldehydes,carboxylic acids,hydrazones,nitriles,alcohols,2-hydroxy indoles,chlorides and other more complex compounds also containing indole ring unit in the structure.Two of them were determined to be indole-3-carboxaldehyde and indole-3-acetamide by comparison with the standard substances.On this basis,the changing trend of the content of each chloramination DBPs against time in the disinfection reaction system with different molar ratios of tryptophan and chloramine was further studied.Finally,a UHPLC-QQQ MS quantitative analysis method for tryptophan was established and optimized.On this basis,the quasi-first-order reaction kinetics constants of the chloramination process of tryptophan at 40 °C,31 °C,22 °C,13 °C and 4 °C were determined.Furthermore,the activation energy of the chloramination disinfection reaction of tryptophan was calculated as 66.410 k J/mol based on Arrhenius Equation.This paper enriches the research on DBPs of amino acids as precursor compounds,and provides ideas and methods for related research on amino acid analogs.