Research Paper
Magnetic covalent-organic frameworks for the simultaneous extraction of eleven emerging aromatic disinfection byproducts in water samples coupled with UHPLC–MS/MS determination

https://doi.org/10.1016/j.jhazmat.2021.127687Get rights and content

Highlights

  • Magnetic covalent-organic frameworks (COFs) were facilely synthesized.

  • Well-synthesized COFs were used for magnetic solid-phase extraction (MSPE).

  • MSPE was applied for emerging pollutants of aromatic disinfection byproducts (DBPs).

  • The MSPE only took 7 min and enabled accurate quantification of stable DBPs in water.

  • The COFs-MSPE-UHPLC–MS/MS method was simple, fast, sensitive and practical for DBPs.

Abstract

A simple method based on magnetic solid-phase extraction (MSPE) was developed for the simultaneous extraction of eleven emerging aromatic disinfection byproducts (DBPs) in water samples coupled with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC–MS/MS) determination. A magnetic covalent-organic framework (COF) material, namely, Fe3O4 @TpBD, was facilely synthesized and fully characterized, followed by an MSPE process. Several important MSPE parameters, such as the magnetic ratio, Fe3O4 @TpBD amount and sample pH, were systematically investigated. Under optimal conditions, the limits of detection and quantification of this COF-MSPE-UHPLC–MS/MS method were as low as 0.07–1.81 ng/L and 0.24–5.99 ng/L, respectively. Good precision was obtained with relative standard deviations (RSDs) of 1.3–10.9% (intraday) and 4.3–15.9% (interday). Furthermore, the validated method was proven applicable to real water samples; for example, the recoveries were 86.8–115.1% for the secondary effluent, and several DBPs in swimming pool water were detected. Notably, the MSPE process required only 7 min, ensuring that the DBPs were relatively stable during the whole analysis process and that Fe3O4 @TpBD demonstrated excellent reusability. The COF-based MSPE method with simplicity, rapidity and efficiency provided an ideal sample pretreatment alternative to determine trace DBPs in complex matrices.

Introduction

Chlorine disinfectants have been widely used to inactivate pathogens and prevent water-borne diseases in the treatment of drinking water, swimming pool water and sewage effluent (Fernandez-Molina and Silva, 2011, Li et al., 2018a, Li et al., 2018b, Pichel et al., 2019). However, chlorine disinfectants easily react with different types of organic matter in the water, including natural organic matter, microorganisms, algae toxins, etc. Consequently, various disinfection byproducts (DBPs) are produced (He et al., 2018, Hu et al., 2018, Hu et al., 2018, Li et al., 2018b, Li et al., 2018, Li and Mitch, 2018, Yang et al., 2019). Long-term drinking of disinfected water may cause bladder cancer (Liu et al., 2020, Nlkolaou et al., 2005). Therefore, the regulations and guidelines of aliphatic DBPs have been formulated for drinking water (USEPA, 2006, WHO, 2006). Currently, some emerging DBPs can be identified and detected (Liberatore et al., 2017, Zhang et al., 2019, Zhang et al., 2019, Zhang et al., 2020, Zhang et al., 2020). Aromatic DBPs have attracted great attention because of their higher toxicity compared with aliphatic DBPs, and they can be decomposed into regular aliphatic DBPs (Liu et al., 2020). Aromatic DBPs are divided into C-DBPs (containing C atoms such as –CHO and –COOH) and N-DBPs (containing N atoms such as –NO2, –Ctriple bondN and –NH2) according to different functional groups (Liu et al., 2020). Due to the different electrostatic potentials of the functional groups, aromatic N-DBPs have higher cytotoxicity and genotoxicity than C-DBPs (Zhang et al., 2018, Zhang et al., 2018, Zhang et al., 2020). Moreover, they are a threat to human health and have adverse effects on the marine environment (Yang and Zhang, 2013). A few aromatic DBPs have unpleasant odors in drinking water (Ma et al., 2016). In addition, bromide/iodide ions can indirectly bring about the presence of aromatic Br-DBPs and I-DBPs (Yang and Zhang, 2013, Hu et al., 2018). Some studies have demonstrated that their toxicity order is I-DBPs > Br-DBPs > Cl-DBPs (Yang et al., 2019). In particular, aromatic Br-DBPs in swimming pool water have been reported to have skin permeability (Xiao et al., 2012), and the new aromatic DBPs found in indoor and outdoor chlorinated swimming pools include 2,4-dichlorophenol, 2,6-dibromo-4-nitrophenol and 2-bromo-6-chloro-4-nitrophenol. Pan et al., 2016a, Pan et al., 2016b detected the concentration of halo 3-hydroxy-2-methylbenzoic acid at 1.7–9.2 ng/L in tap water. Fan et al. (2013) found 0.50–13 ng/L aromatic DBPs in effluent water from drinking water treatment plants. Considering the health risks caused by emerging aromatic DBPs, it is of great necessity to monitor their contents.

High-performance liquid chromatography (HPLC) (Dahl et al., 2012) and ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC–MS/MS) (Zhai et al., 2014) have been used to determine aromatic DBPs. However, it is still imperative to combine effective sample pretreatment techniques for the cleanup and enrichment of ultratrace aromatic DBPs before instrumental analysis since the aromatic DBPs in environmental water are usually at the ng/L level. Currently, there are few studies on the pretreatment methods of emerging aromatic DBPs, only liquid-liquid extraction (LLE) (Jiang et al., 2017, Jiang et al., 2017, Zhang et al., 2020, Zhang et al., 2020) and solid-phase extraction (SPE) (Fernandez-Molina and Silva, 2011, Hu et al., 2018). The LLE method usually consumes a large amount of organic solvent; for example, 100 mL of methyl tert-butyl ether (MtBE) is used to extract the targets from water samples, which undoubtedly violates the concept of green chemistry (Zhang et al., 2020, Zhang et al., 2020). The SPE method usually adopts an SPE column to extract and concentrate the targets. The clogging of the column and cumbersome equipment have always been difficult to overcome. It is worth mentioning that research on the stability of aromatic DBPs is limited; for example, they are easily hydrolyzed (Gong and Zhang, 2015, Pan et al., 2016b), photolyzed (Liu et al., 2017, Liu et al., 2019), or susceptible to the influence of residual chlorine in water (Gong et al., 2016, Jiang et al., 2017, Jiang et al., 2017). Therefore, it is necessary to apply quenching agents to stabilize the aromatic DBPs in water before analysis (Gong et al., 2016). This will inevitably increase the pretreatment time and cause the degradation risk of aromatic DBPs. Therefore, it is urgently necessary to develop fast, facile and powerful sample pretreatment methods for emerging aromatic DBPs. Compared with traditional pretreatment technologies, magnetic SPE (MSPE) has the remarkable advantages of simplicity, easy operation and rapid separation from water samples (Li et al., 2018a, Li et al., 2018b). We have applied this technology to the analysis and removal of pollutants in water (Ma et al., 2020, Ma et al., 2018). The key to MSPE technology is the selection and preparation of magnetic adsorbents.

Covalent-organic frameworks (COFs) are porous polymers with covalent bonds that form a network (Zheng et al., 2020, Xu et al., 2020). Because of their high stability, strong function, large porosity and specific surface area, and modification variety, COFs have been widely used in gas storage (Van der Jagt et al., 2021), catalysis (Wang et al., 2020, Wang et al., 2020), sensing (Liu et al., 2019, Liu et al., 2019) and so on. Due to the particular structure of COFs, they can form hydrogen bonds, π-π conjugation and hydrophobic interaction forces with pollutants (Wen et al., 2020) and thereby show outstanding adsorption capacity. Hence, they have also been used to remove and analyze pollutants (Li et al., 2019, Chen et al., 2019, Zhuang et al., 2020). However, COFs are highly hydrophobic and difficult to separate from water due to their low density, limiting their applications (Chen et al., 2019, Li et al., 2018a, Li et al., 2018b). Magnetic functionalization of COFs can solve the above problems (Zhang et al., 2019, Zhang et al., 2019). For example, Li et al., 2018a, Li et al., 2018b employed magnetic TpBD to extract six steroidal and phenolic endocrine-disrupting chemicals in food (Li et al., 2018a, Li et al., 2018b). Pang et al. (2020) used a mechanical grinding method to prepare magnetic TpBD and applied it to enrich fifteen kinds of phthalate esters in beverage samples.

Therefore, magnetic TpBD was utilized in this work for vortex-assisted MSPE of eleven aromatic DBPs, combined with UHPLC–MS/MS detection. To the best of our knowledge, this is the first application of magnetic COFs to analyze emerging aromatic DBPs in water. The magnetic TpBD COF adsorbent was synthesized by a facile approach and well-characterized, followed by use in MSPE. Several factors affecting the MSPE efficiency were studied in detail, including the magnetic ratio, amount of magnetic TpBD and pH. Then, the recyclable use of the TpBD was investigated and the analytical performance of the COFs-MSPE-UHPLC–MS/MS method. Finally, the method was successfully applied to analyze eleven emerging aromatic DBPs in tap water, swimming pool water, and effluents of sewage plants.

Section snippets

Chemical reagents and water samples

Hydrochloric acid and methanol were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Tetrahydrofuran (THF) was purchased from Fuyu Chemical Co., Ltd. (Tianjin, China). Iron oxide (Fe3O4) was obtained from Macklin Biochemical Co., Ltd. (Shanghai, China). 2,4,6-triformylphloroglucinal (Tp) was supplied by TCI Chemical Co., Ltd. (Shanghai, China). Benzidine (BD) was purchased from Aladdin Chemical Reagent Co., Ltd. (Shanghai, China). Chromatography grade methanol for

Stability of aromatic DBPs

According to reports, the transformation among DBPs can be generated under heat, solar radiation and residual disinfectants in water (Liu et al., 2017, Liu et al., 2019, Liu et al., 2019, Pan et al., 2014). The conversion between aromatic DBPs affects water safety, so evaluating their stability is very important. However, there are no reports on the systematic investigation of their stability time to the best of our knowledge. Herein, we investigated the stability of eleven kinds of aromatic

Conclusions

To conclude, this work systematically investigated the stability of eleven emerging aromatic DBPs. An efficient and rapid MSPE method based on magnetic COF (TpBD) was developed. It can rapidly enrich eleven aromatic DBPs within 7 min and validly avoid their decomposition. The magnetic composites were easily collected and reused ten times with excellent stability. Moreover, the established COFs-MSPE-UHPLC–MS/MS method showed high sensitivity, with LODs ranging from 0.07 to 1.81 ng/L. In

CRediT authorship contribution statement

Shuang Li: Methodology, Investigation, Formal analysis, Writing – original draft. Jiping Ma: Project administration, Validation, Supervision, Funding acquisition, Writing – review & editing. Gege Wu: Investigation, Formal analysis. Jinhua Li: Methodology, Writing – review & editing. Xiaoyan Wang: Writing – review & editing. Lingxin Chen: Supervision, Validation, Writing – review & editing.

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.

Acknowledgments

The authors acknowledge the financial support from the National Natural Science Foundation of China (21976099, 21876199, 21804010, 22176210), the Natural Science Foundation of Shandong Province of China (ZR2019MB046), and the Taishan Scholar Project Special Funding (ts20190962).

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