Chlorinated and brominated forms of salicylic acid (SA) have recently been identified as a new class of disinfection byproducts (DBPs) in drinking water. Herein, we report the inherent reactivity of several aqueous halogenating agents toward hydrogen salicylate, the predominant species of salicylic acid under environmental conditions. Using synthetic waters, halogenation rates associated with the formation of 3-chloro, 5-chloro, 3-bromo, and 5-bromosalicylate were measured as a function of pH, [Cl − ], [Br − ], free chlorine dose, and the initial concentration of SA. Halogenating-agent specific second-order rate constants were determined and decrease in the order: BrCl > BrOCl > Br 2 > Br 2 O > Cl 2 > Cl 2 O > HOBr > HOCl. Chloride is capable of enhancing rates of bromination and chlorination, ostensibly by promoting the formation of BrCl and Cl 2 , both of which are several orders of magnitude more inherently reactive than HOBr and HOCl, respectively. Kinetic data also support the participation of salicyloyl hypochlorite as a chlorination intermediate capable of influencing chlorination rates at pH >8. Experiments in which buffer concentrations were varied indicate that phosphate buffers can enhance rates of SA bromination but not chlorination; carbonate and borate buffers did not appreciably influence rates of bromination or chlorination. Under conditions representative of chlorinated drinking water, rates of SA bromination will generally exceed rates of SA chlorination. The results discussed herein demonstrate the importance of considering halogenating agents beyond HOBr and HOCl when developing kinetic models to describe and predict halogenation rates and selectivity in waters containing free chlorine.
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Applications of 1,3,5-trimethoxybenzene as a derivatizing agent for quantifying free chlorine, free bromine, bromamines, and bromide in aqueous systems
Free chlorine and free bromine ( e.g. , HOCl and HOBr) are employed as disinfectants in a variety of aqueous systems, including drinking water, wastewater, ballast water, recreational waters, and cleaning products. Yet, the most widely used methods for quantifying free halogens, including those employing N , N -diethyl- p -phenylenediamine (DPD), cannot distinguish between HOCl and HOBr. Herein, we report methods for selectively quantifying free halogens in a variety of aqueous systems using 1,3,5-trimethoxybenzene (TMB). At near-neutral pH, TMB reacted on the order of seconds with HOCl, HOBr, and inorganic bromamines to yield halogenated products that were readily quantified by liquid chromatography or, following liquid–liquid extraction, gas chromatography-mass spectrometry (GC-MS). The chlorinated and brominated products of TMB were stable, and their molar concentrations were used to calculate the original concentrations of HOCl (method quantitation limit (MQL) by GC-MS = 15 nmol L −1 = 1.1 μg L −1 as Cl 2 ) and HOBr (MQL by GC-MS = 30 nmol L −1 = 2 μg L −1 as Cl 2 ), respectively. Moreover, TMB derivatization was efficacious for quantifying active halogenating agents in drinking water, pool water, chlorinated surface waters, and simulated spa waters treated with 1-bromo-3-chloro-5,5-dimethylhydantoin. TMB was also used to quantify bromide as a trace impurity in 20 nominally bromide-free reagents (following oxidation of bromide by HOCl to HOBr). Several possible interferents were tested, and iodide was identified as impeding accurate quantitation of HOCl and HOBr. Overall, compared to the DPD method, TMB can provide lower MQLs, larger linear ranges, and selectivity between HOCl and HOBr.
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- Award ID(s):
- 1651536
- NSF-PAR ID:
- 10120530
- Date Published:
- Journal Name:
- Analytical Methods
- ISSN:
- 1759-9660
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9AY01443H
