Ultra trace determination of bromate in mineral water and table salt by liquid chromatography–tandem mass spectrometry

doi:10.1016/j.talanta.2012.06.076

Talanta

Volume 99, 15 September 2012, Pages 677-682

https://doi.org/10.1016/j.talanta.2012.06.076 Get rights and content

Abstract

A liquid chromatography–tandem mass spectrometry method (LC–MS/MS) was developed in order to determine the bromate in mineral water and table salt. The following optimum conditions for the LC–MS/MS detection were established: derivatization reagent (300 mg/L of 2,6-dimethylaniline), acidity (0.2 M HCl), reaction temperature (30 °C) and heating time (20 min). The formed derivative was directly injected in the LC system without extraction or purification procedures. In the established conditions, the method was used to detect bromate in mineral water and table salt. The limit of detection and limit of quantification of bromate in mineral water were 0.02 μg/L and 0.07 μg/L, respectively, and those of table salt were 0.07 μg/kg and 0.23 μg/kg, respectively. The 17 common ions did not interfere even when present in 1,000-fold excess over the bromated ion of 10.0 μg/L. The accuracy was in a range of 92–104% and the assay precision was less than 9% in the table salt. The method was successfully applied to determine bromate in mineral water and table salt.

Highlights

► This method is directly used to determine bromate by LC–MS/MS after derivatization. ► Selection of reagent and its amount, reaction temp. and time and pH were optimized. ► Best reagent is 2,6-DMA. ► LOD and LOQ in table salt were 0.07 and 0.23 μg/kg respectively and RSD was less than 9.0%.

Introduction

Bromate is a disinfection by-product (DBP) that is generated during disinfection processes through the reaction of ozone and bromide in municipal drinking water [1], [2]. Bromate is a potential carcinogen, which has been proven by both the US Environmental Protection Agency (EPA) and the International Agency for Research on Cancer [3], [4]. Due to these health concerns, the bromated concentration in drinking water is a significant concern among regulatory agencies worldwide [5], [6], [7], [8]. Regulatory agencies in the USA [6] and European countries [7] have established a maximum contaminant level of bromate of 10.0 μg/L in drinking water, and Korea [8] has a standard level of the same concentration only in natural mineral water.

Considerable interest has been shown in bromate analysis due to its toxicology; a number of methods have been developed to manage the variety of water matrices using ion chromatography (IC) [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31]. In fact, the bromate quantity can be determined at sub-μg/L levels using pre-concentration techniques [12], [14]. Alternative and sensitive detection techniques include post-column derivatization [10], [28], [29] and mass detection [17], [18], [19], [20], [21], [22], [23], [24], [25], [30], [31], however, these methods suffer from complex plumbing operations. Gas chromatographic mass spectrometric methods (GC–MS) [32], [33], [34] following the redox reaction of bromate and extraction have been developed to detect bromate in complex matrices. These methods can analyze bromate with very low detection limits and without chloride interferences, but they involve multistep reactions including the removal of free bromide [32] and the solvent extraction and concentration before the injection in GC–MS [34], while also suffering from interference in chlorinated waters [33].

A liquid chromatography–tandem triple-quadrupole mass spectrometry (LC–MS/MS) is a common technique in the analytical area and is routinely used to automatically analyze many types of compounds. Several analytical methods for determining the bromate in drinking water or food have been developed using LC–MS/MS [35], [36], [37]; however, these methods suffer from interference of ions such as sulfate and carbonate. In particular, it has been difficult to evaluate the occurrence of the chemical in samples containing high concentration levels of ions such as seawater and salt.

The aim of this study is to develop a simple and sensitive bromate determination method using the LC–MS/MS but without the interference of various ions. Several derivatization tests were performed in order to select a reagent with a high sensitivity and low interference in the derivative and to optimize the parameters of LC–MS/MS for automatically analyzing bromate in natural mineral water and table salt. The new method was applied in real sample analyses.

Section snippets

Reagents

Sodium chloride (99.5%), potassium iodide (99.9%), potassium bromide (99%), potassium bromate (99.8%), 2,6-dimethylphenol (2,6-DMP, 99.0%), 2,6-dimethylaniline (2,6-DMA, 99%), 2,6-diisopropylphenol (2,6-DiPP, 97%), 2,6-di-tert-butylphenol (2,6-DtBP, 99%), chlorpromazine hydrochloride (99.9%), trifluoperazine dihydrochloride (99%), o-dianisidine (99.9%), acetanilide (99.9%) and 2-naphthol (99%) were obtained from Aldrich (Milwaukee, WI, USA). A stock standard solution of bromate was freshly

Selection of derivatization reagent

A derivatization method has been described for the sensitive LC–MS/MS analysis of bromate. In acidic media, bromate is reduced by chloride ion to form bromine, which reacts with the active hydrogen of reagents to form bromo-derivatives through the reaction [32], [34]2BrO₃⁻+10Cl⁻+12H⁺→Br₂+5Cl₂+6H₂OBr₂+reagent→bromo-derivative+Br⁻

The formed derivative was designed to be directly injected into the LC system without an extraction procedure. For the direct injection, the derivative must be sensitive

Conclusion

Major advantages of this method are as follows: (1) The proposed method sensitively determined bromate without interference from various ions in mineral water and table salts. Acceptable precision and accuracy were obtained in the samples with the complex matrices. (2) Although this method requires a derivatization step in comparison with other LC–MS/MS methods, the procedure is simple and rapid, and is not laborious. (3) This method can be used in drinking water, co-existing residual oxidants

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Drinking water is an important source of human exposure to bromate, an ubiquitous environmental contaminant and a suspect human carcinogen. Nevertheless, little is known with regard to bromate exposure from water produced by thermal desalination of seawater. The purpose of this study was to determine the occurrence of bromate in desalinated drinking water and groundwater from Kuwait and estimate associated exposure and health risks to consumers. In this study, 194 tap and ground water samples collected from Kuwait were analyzed for the presence of bromate and bromide (reduced form of bromine). Bromate was found in almost all tap water samples with a mean concentration of 19.6 μg/L, which is higher than the maximum acceptable contaminant level (MCL) of 10 μg/L. The mean concentration of bromide in tap water samples was 46.2 μg/L. In bottled water, lower mean bromate concentration was found (2.89 μg/L) with mean bromide levels at 76.1 μg/L. Saline brackish water had bromate concentration at 9.48 μg/L while bromate was not detected in saline groundwater/well water samples. The mean estimated daily intake (EDI) of bromate by the Kuwaiti population through tap water and commonly consumed bottled water was 21.7 μg/d and 3.21 μg/d, respectively. Among the five age groups, 3 to 5-year-old children had the highest EDI of bromate at 15.4 μg/d. The excess cancer risk due to ingestion of bromate in tap water was estimated to be 3.92 × 10⁻⁴, which is approximately one order of magnitude higher than the maximum acceptable level of risk (2× 10⁻⁵). This study highlights the significance of desalinated water as a source of bromate exposure.
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The maximum allowable level of bromate in drinking water established by both the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO) is 10 μg/L (Zhang et al., 2016). Unfortunately, recent studies have shown that bromate is presented not just in water, but in potato snacks (Arias et al., 2010), flour (Yan et al., 2016), bread and bread additives (Shi, Liang, Cai, & Mou, 2006), and other foods (Kim & Shin, 2012). Therefore, although many countries have prohibited or reduced the use of bromate in the food industry, there is also a need for development of analytical technologies for bromate analysis in foods.
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Hence, the ongoing efforts for developing highly sensitive and yet affordable methods for monitoring and subsequent removal of BrO3− in drinking water as well as in food products are essential. Conventional techniques have been used for the detection and quantification of BrO3− such as chromatographic [9–11] and spectrofluorometric methods [12]. These methods usually rely on sophisticated instruments and require laborious extraction process of bromate ions.
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Bromine and water quality - Selected aspects and future perspectives
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Bromine is a microelement present in waters, both in inorganic and in a wide range of organic compounds, though at lower concentrations. Typically, concentrations of organobromine compounds in waters are several orders of magnitude lower than of bromides. Two issues are addressed in the paper: the influence of bromides on the quality of treated waters and organobromines as contaminants of natural waters. Bromide presence in treated water gives rise to formation of potentially mutagenic disinfection by-products (DBPs). Registered amounts of DBPs in potable waters, exceeding the admissible levels, and the published data on DBPs in waters used for leisure and recreation activities, clearly indicate the health risk. Major sources are identified and registered concentrations of EDB, DBCB, methyl bromide, bromacil and PBDEs in the aquatic environment are summarized. The effects of bromide on DBPs formation and numerous examples of organobromine contamination of the aquatic environment indicate that the presence of bromides and organobromine compounds in the aquatic environment will have to be given more consideration, for several reasons. Firstly, larger amounts of bromide are present in saline and contaminated waters and the proportion of such waters being handled is increasing. Similarly, the processes of water purification, treatment and disinfection are now playing a major role. Secondly, emissions from manufacturing of bromine-containing materials growing, due to, inter alia, intensive development of the electronic industry and the plastic manufacturing sector. Thirdly, bromine compounds are also used as medicine ingredients. There is now a growing awareness of the presence of pharmaceuticals in the aquatic environment. Fourth, low bromide concentrations in hypergene zones may be modified in the future, partly because of the climate changes, which may give rise to difficulties with water treatment systems.
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Thus, selective methods are necessary for BrO3− determination at trace levels. Several chromatographic methods have been reported for bromate determination at sub-μg L−1 level to mg L−1 e.g., ion chromatography (IC) with conductivity detection (IC–CD) [6,10–15], IC with atmospheric pressure ionization-mass spectrometry (IC/API-MS) and IC with inductively coupled plasma mass spectrometry (IC/ICP–MS) [16], liquid chromatography–tandem mass spectrometry method (LC–MS/MS) [10], headspace solid – phase microextraction coupled with GC–MS [17], and liquid–liquid extraction followed by GC–MS [18]. IC–CD has been documented by the US environmental protection agency (EPA) and International Organization for Standardization (ISO) as an official method for monitoring bromate concentration with LOD of 20.0 μg L−1 [10].
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Ultra trace determination of bromate in mineral water and table salt by liquid chromatography–tandem mass spectrometry

Abstract

Highlights

Introduction

Section snippets

Reagents

Selection of derivatization reagent

Conclusion

Chemosphere

Anal. Chim. Acta

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

Talanta

J. Chromatogr. A

Anal. Chim. Acta

J. Chromatogr. A

Anal. Chim. Acta

J. Chromatogr. A

Ozone News

Environ. Sci. Technol.