1,3,5-Trimethoxybenzene (TMB) as a new quencher for preserving redox-labile disinfection byproducts and for quantifying free chlorine and free bromine
1,3,5-Trimethoxybenzene (TMB) as a new quencher for preserving redox-labile disinfection byproducts and for quantifying free chlorine and free bromine
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DOI：
10.1039/c8ew00062j
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发表时间：
2018-07-01
影响因子：
5
通讯作者：
Sivey, John D.
中科院分区：
文献类型：
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作者：
Lau, Stephanie S.;Dias, Ryan P.;Sivey, John D.
在饮用水、废水和娱乐用水中消毒副产物(DBPs)的研究中，通常使用亚硫酸钠、硫代硫酸钠和抗坏血酸来淬灭游离氯和游离溴。然而，这些猝灭剂的还原能力可能会导致一些氧化还原不稳定的分析物的降解。氯化铵是另一种常见的猝灭剂，它将游离氯转化为一氯胺，因此不适合用于对氯胺化敏感的分析物。在这里，我们证明了1，3，5-三甲氧基苯(TMB)作为游离氯和游离溴的猝灭剂的用途。TMB对游离氯的反应性已在前面进行了表征。本文用竞争动力学方法定量了TMB与游离溴的反应活性(KHOBr3.35×106M-1 S-1)。为了探索TMB作为无卤素猝灭剂用于动力学实验的可行性，对2，4-二氯苯酚的氯化反应、苯甲醚的溴化反应以及二甲基亚胺-P的氯化和溴化反应进行了考察。尽管TMB与游离氯或游离溴的反应速度不如某些(但不是全部)传统猝灭剂那样快，但以TMB(相对于硫代硫酸盐)作为猝灭剂时，其实验速率常数总体上没有显著差异。通过监测TMB的氯化和溴化产物，对淬火样品中的游离卤素残留量进行了定量。此外，TMB不影响在传统猝灭剂存在下否则会降解的DBPs(例如，氯苦和溴乙腈)的稳定性。因此，在涉及氧化还原不稳定分析物的水溶液卤化实验中和/或当需要选择性地定量残留的游离卤素时，TMB可以作为游离氯和游离溴的合适的猝灭剂。
Sodium sulfite, sodium thiosulfate, and ascorbic acid are commonly used to quench free chlorine and free bromine in studies of disinfection byproducts (DBPs) in drinking water, wastewater, and recreational water. The reducing capabilities of these quenchers, however, can lead to the degradation of some redox-labile analytes. Ammonium chloride, another common quencher, converts free chlorine into monochloramine and is therefore inappropriate for analytes susceptible to chloramination. Herein, we demonstrate the utility of 1,3,5-trimethoxybenzene (TMB) as a quencher of free chlorine and free bromine. The reactivity of TMB toward free chlorine was characterized previously. The reactivity of TMB toward free bromine was quantified herein (kHOBr, TMB = 3.35 x 106 M-1 s-1) using competition kinetics. To explore the feasibility of TMB serving as a free halogen quencher for kinetic experiments, chlorination of 2,4-dichlorophenol, bromination of anisole, and chlorination and bromination of dimethenamid-P were examined. Although TMB does not react with free chlorine or free bromine as quickly as do some (but not all) traditional quenchers, there was generally no significant difference in the experimental rate constants with TMB (relative to thiosulfate) as the quencher. By monitoring the chlorination and bromination products of TMB, free halogen residuals in quenched samples were quantified. Furthermore, TMB did not affect the stabilities of DBPs (e. g., chloropicrin and bromoacetonitriles) that otherwise degraded in the presence of traditional quenchers. TMB could, therefore, be an appropriate quencher of free chlorine and free bromine in aqueous halogenation experiments involving redox-labile analytes and/or when selective quantification of residual free halogens is desired.