Fast determination of nine haloacetic acids, bromate and dalapon in drinking water samples using ion chromatography–electrospray tandem mass spectrometry

https://doi.org/10.1016/j.chroma.2020.461052Get rights and content

Highlights

  • Fast and sensitive determination of haloacetic acids by IC/MS/MS.

  • Direct trace level analysis of haloacetic acids.

  • 33% faster than the current EPA method 557.

Abstract

Ion chromatography–electrospray tandem mass spectrometry (IC-ESI-MS/MS) is used to determine nine haloacetic acids (HAAs), bromate, and dalapon in drinking water samples in U.S. EPA Method 557. In this method, all target analytes are separated and measured with good sensitivity without the need for sample preconcentration or derivatization. However, the separation time is relatively long. In order to reduce the sample analysis time in EPA Method 557, a new anion exchange column has been developed to perform fast separation of the target analytes. Using this new anion exchange column, nine HAAs, bromate, and dalapon can be resolved and separated from interfering matrix ions within 40 minutes, about 33% faster than the analysis time obtained using an earlier anion exchange column reported in EPA Method 557. The new anion exchange column has unique selectivity and high exchange capacity. Method optimization, simplification and improvements in robustness are demonstrated while validating the new column suitability for the determine of HAAs, bromate and dalapon according to EPA Method 557.

Introduction

Haloacetic acids (HAAs) are a class of widespread undesirable disinfection by-products formed during the disinfection process of drinking water in which routine water disinfectants such as chlorine or chloramine is used to kill pathogenic microorganisms. There are nine major HAAs, including monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), monobromoacetic acid (MBAA), dibromoacetic acid (DBAA), tribromoacetic acid (TBAA), bromochloroacetic acid (BCAA), bromodichloroacetic acid (BDCAA), and chlorodibromoacetic acid (CDBAA). Because of their suspected carcinogenicity, mutagenicity, as well as the developmental, reproductive and hepatic toxicity [1], [2], [3], [4], the World Health Organization (WHO) [5] has established guidelines for these disinfection by-products in drinking water. In the U.S., these disinfection by-products are regulated by the Environmental Protection Agency (EPA) as a part of the Safe Drinking Water Act. In 1998, the Stage 1 Disinfectants and By-products Rule was published, which set the limit for total trihalomethanes at 80 µg L−1 and, for the first time, set the maximum contamination levels for the sum of the five HAAs (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid) at 60 µg•L-1. It also sets a maximum contaminant level goal for dichloroacetic acid to zero and trichloroacetic acid to 30 µg L−1. In the Stage 2 Disinfectants and By-products Rule, the maximum contaminant level goal for trichloroacetic acid is reduced to 20 µg L−1 and monochloroacetic acid is set at 70 µg L−1 [6]. Ozone is a powerful drinking water disinfectant that is effective in treating chlorine resistant organisms, such as cryptosporidia [7]. For bottled water, ozonation is generally preferred over other available disinfection treatment methods because it does not leave a taste or residual disinfectant, due to the short lifetime of ozone. Ozone also improves the quality of finished drinking water by reducing filtered water turbidity and decreasing the formation of many halogenated disinfection by-products. Thus, some water utilities use a combination of chlorination and ozonation for the disinfection processes. However, ozonation of drinking water containing bromide can result in the formation of bromate, a potential human carcinogen even at low μg L−1 concentration [4]. The U.S. EPA and European Commission have established a regulatory maximum contaminant level of 10 μg L−1 bromate in drinking water [5,6]. Dalapon is an herbicide used to control grasses in a wide variety of crops, including fruit trees, beans, coffee, corn, cotton, and peas. Dalapon is also registered for use in a number of non-crop applications such as lawns, drainage ditches, along railroad tracks, and in industrial areas. Some people who drink water containing Dalapon well in excess of the maximum contaminant level for many years could experience kidney changes. The U.S. EPA has set a maximum contaminant level for dalapon at 200 µg L−1. [8] The other 4 HAAs (tribromoacetic acid, bromochloroacetic acid, bromodichloroacetic acid and chlorodibromoacetic acid) are monitored in the analysis as well to follow Unregulated Contaminant Monitoring Rule [9].

Gas chromatography (GC) with electron capture detection and GC equipped with mass spectrometry (GC-MS) are commonly used to analyze HAAs after sample acidification, extraction and derivatization [10], [11], [12], [13]. However, these two methods involve tedious labor-intensive sample preparation and the use of carcinogenic reagents in analyte derivatization. Liquid chromatography tandem mass spectrometry (LC–MS or LC - MS/MS) is an alternative analytical technique due to its sensitivity and specificity for determination of HAAs [14], [15], [16]. Ion-exchange liquid chromatography and hydrophilic interaction liquid chromatography are used to increase the retentivity and separation of these small, charged polar molecules such as HAAs, but even with preconcentration of samples, the required detection limits can barely be met due to the limited instrumental sensitivity possibly caused by the suppression of additives [17,18]. In the U.S. EPA Method 557 [19], ion chromatography – electrospray tandem mass spectrometry (IC-ESI-MS/MS) is used to determine haloacetic acids, bromate, and Dalapon in drinking water samples. All the targeted analytes are separated and analyzed without preconcentration and derivatization in a total analysis time of about 60 minutes. In 2017, the U.S. EPA has approved Method 557.1, which uses a two-dimensional ion chromatography technique for haloacetic acids analysis [20].

In this study, we report the use of a new anion exchange column for the determination of nine haloacetic acids, bromate and Dalapon at trace levels in drinking water samples using IC-MS/MS. The new IC-MS/MS method determines these target analytes in water samples in 40 minutes, delivering 33% faster analysis time relative to that obtained using EPA Method 557. Organic solvents such as isopropanol and acetonitrile have been used as the make-up flow solvent to increase the ionization at MS source in the IC/MS methods. The unique selectivity and high loading capacity of the IonPac AS31 column enables a simpler instrumental setting by eliminating the use of organic solvent and an extra auxiliary pump for the makeup flow, achieving a simpler, more robust and lower cost workflow.

Section snippets

Reagents

The haloacetic acid standard containing monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid, tribromoacetic acid, bromochloroacetic acid, bromodichloroacetic acid, and chlorodibromoacetic acid (1000 µg•mL-1 each in methyl-tert-butyl-ether) was purchased from Restek (Bellefonte, PA). Both Dalapon and bromate were purchased from Chem Service (West Chester, PA). The internal standards including monochloroacetic acid-2-13C, dichloroacetic

Optimization of IC–MS conditions

EPA method 557 uses IonPac AS24 columns to perform the separation of target analytes including nine HAAs, bromate and dalapon. While IonPac AS24 columns provide good separation of target analytes, the separation time of 60 min is relatively long. The long separation time hinders the throughput of sample analysis. To address this analytical challenge, we recently developed a new IonPac™ AS31 anion exchange separation column. The anion exchange stationary phase in the AS31 columns consists of a

Conclusions

A fast, sensitive and simple method was developed for direct analysis of nine HAAs, bromate and dalapon for drinking water samples using IC-MS/MS without any sample pretreatment. The IonPac AS31 column based on hyper-branched anion exchange condensation polymer provides a unique selectivity which allows a simple and fast separation method for 9 HAAs, bromate and dalapon from common interference anions in a total analysis time of 40 min, which is 33% faster than the total analysis time of EPA

CRediT authorship contribution statement

Xin Zhang: Conceptualization, Data curation, Methodology, Formal analysis, Writing - original draft. Charanjit Saini: Conceptualization, Data curation, Methodology, Formal analysis, Writing - original draft. Chris Pohl: Conceptualization, Data curation, Formal analysis, Writing - original draft. Yan Liu: Conceptualization, Formal analysis, Writing - original draft.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Thermo Scientific™ TSQ Fortis™ Mass Spectrometer support provided by Claudia Martins, Cristina Jacob, and Michael Volny of Thermo Fisher Scientific is greatly achnowledged.

References (23)

  • U.S. Environmental Protection Agency, Stage 1 and stage 2 disinfectants and disinfection byproducts rules website,...
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