Spherical conjugated microporous polymers for solid phase microextraction of carbamate pesticides from water samples

https://doi.org/10.1016/j.chroma.2020.461360Get rights and content

Highlights

  • Spherical sp2 carbon-conjugated microporous polymers (sp2c-CMPs) were prepared.

  • Surface areas of sp2c-CMPs can be regulated by inorganic salt.

  • sp2c-CMPs were used as solid-phase microextraction (SPME) coating.

  • SPME method was established for detecting carbamate pesticides in water.

Abstract

Conjugated microporous polymers (CMPs) with uniform morphology have shown fascinating application in the separation science. In this study, metal-free Knoevenagel condensation was adopted to prepare spherical sp2 carbon-conjugated microporous polymers, which used tetrakis(4-formylphenyl)methane and 1,4-phenylenediacetonitrile as monomers. Due to the remarkable extraction capability for carbamate pesticides (CPs), the as-synthesized CMPs were fabricated as the coating for solid-phase microextraction (SPME). After optimized SPME parameters (adsorption time, salt concentration, sample pH, adsorption temperature, desorption time, desorption solvent and desorption volume), ten CPs in water samples were quantified by ultrahigh performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Linearity in the range 0.005–100 ng mL−1 with low detection limits of 0.00060–0.017 ng mL−1 was obtained. The intra-day and inter-day precisions expressed as relative standard deviations were 1.5–8.1% and 1.1–8.0%, respectively. Fiber-to-fiber reproducibility was below 7.3%. The CMPs-SPME-UPLC-MS/MS method was applied to detect trace CPs in real water samples with relative recoveries from 91.8% to 108%.

Introduction

Carbamate pesticides (CPs) are widely used in agriculture and forestry as fungicides, insecticides, molluscicides, miticides, and nematocides due to their high efficacy, low cost, and broad spectrum of biological activity [1]. However, inappropriate or extensive use can lead to environmental contamination [2]. Thus, considerable techniques have been devoted for the sensitive detection of CPs, including high performance liquid chromatography (HPLC) [2], [3], [4], gas chromatography (GC) [5], gas chromatography-mass spectrometry (GC–MS) [6,7], and liquid chromatography-tandem mass spectrometry (LC-MS/MS) [8,9]. Efficient sample pretreatment is a key step for the sensitive and accurate determination of CPs due to the complexity of sample matrices and their low concentration. As a great promising sample preparation technique, solid-phase microextraction (SPME) has gained wide acceptance which stems from its multiple merits (solvent-free, simple, sensitivity, integrate sampling, extraction and concentration into one step) [10,11]. It has been employed for the enrichment of compounds from pharmaceutical, environmental, food, and biological samples [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. As the critical factor for SPME, various materials have been explored as the coatings, such as conjugated microporous polymers (CMPs) [13,25], metal-organic frameworks [14], [15], [16], covalent organic frameworks [17,18], and hyper-crosslinked polymer [24]. Importantly, the morphologies of materials can significantly influence the microextraction performance [11,26]. Therefore, there has been growing interest in the development of SPME adsorbent with uniform morphology.

As an emerging class of amorphous porous organic materials, CMPs are composed of aromatic compound by cross-coupling reactions [27]. Due to the good stability, mechanical rigidity and excellent porosity, CMPs have been used for optical applications [28], gas storage [29], catalysis [30], electronic devices [31] and adsorbents [25,[32], [33]. Several conventional reactions including Suzuki coupling [31], Yamaoto coupling [34], Sonogashira-Hagihara coupling [35], and Friedel-Crafts reaction [36] have been utilized to synthesize CMPs. Due to the use of noble metals as catalysts, fabricating of CMPs by facile and universal synthetic protocols remains a formidable challenge. It is pivotal to seek novel approaches which without metal catalysts. Knoevenagel condensation is a potential cost-effective methodology that can obtain sp2 carbon-conjugated microporous polymers (sp2c-CMPs). As reported, these materials obtained by Knoevenagel condensation show different morphologies such as core-shell structure [37], irregular block [38], and sheet-like flakes [39]. Even though the great achievements have been made in the morphological control, the synthesis of sp2c-CMPs with uniform sphere remains to be solved.

In this work, sp2c-CMPs were synthesized using tetrakis(4-formylphenyl)methane (TFPM) and 1,4-phenylenediacetonitrile (PDAN) as monomers via Knoevenagel reactions which is named as TpPn-CMPs (Fig. S1). The uniform morphology of TpPn-CMPs can be regulated by Na2SO4. After the TpPn-CMPs were coated on the surface of fiber, the effecting SPME factors were investigated and optimized in detail. Compared with commercial adsorbents and sp2c-CMPs with irregular morphologies, the TpPn-CMPs show the best microextraction capacity for CPs. Finally, the SPME coupling with ultrahigh performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was applied to analyze target CPs in environment water samples.

Section snippets

Materials

Mesitylene, 1,4-dioxane, tetrahydrofuran (THF) and dichloromethane (CH2Cl2) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). NaOH, Na2SO4, Mg2SO4 and K2CO3 were acquired from Kemiou Chemical Reagent Co., Ltd. (Tianjin, China). Formic acid (FA) and trifluoroacetic acid (TFA) were purchased from J&K (Beijing, China). TFPM and PDAN were supplied by Yanshen Technology Co., Ltd. (Jilin, China). The HPLC grade methanol (MeOH) and acetonitrile (ACN) were brought from Merck

Synthesis and characterization of TpPn-CMPS

According to the literature, sp2c-CMPs can be prepared via conventional solvothermal method (Table S3, entry 1) [40]. As shown in Fig. 1, however, irregular morphology is obtained. Recently, Faul and coworkers reported that CMPs can be regulated by adding inorganic salts [41]. Thus, inorganic salts including MgSO4, K2CO3 and Na2SO4 were verified. Under the regulation of Na2SO4, interestingly, the TpPn-CMPs display uniform spherical nanoparticles with the size of around 700 nm (Fig. 1). As shown

Conclusion

In summary, TpPn-CMPs with uniform sphere were synthesized and employed as SPME adsorbents. The TpPn-CMPs coated fibers possessed higher extraction efficiency than irregular morphology CMPs coated fibers and PA, PDMS/DVB, PDMS, and C18 SPME fibers. Under optimal conditions, the TpPn-CMPs-SPME was combined with UPLC-MS/MS to detect trace CPs in environmental waters with wide linear ranges, low detection limits, excellent precisions, and good relative recoveries.

Declaration of Competing Interest

The authors declare no conflict of interest.

CRediT authorship contribution statement

Rongyu Wang: Investigation, Methodology, Writing - original draft. Xiaowei Sun: Writing - review & editing. Xiao Wang: Writing - review & editing. Jie Chen: Writing - review & editing, Funding acquisition. Bin Wang: Writing - review & editing, Funding acquisition. Wenhua Ji: Conceptualization, Funding acquisition.

Acknowledgments

We acknowledge financial support of this work from the National Natural Science Foundation of China (31972145, 21771087 and 21703080), the NSF of Shandong Province (ZR2017MB007 and ZR2017BB010), Taishan Scholar Program of Shandong Province (tsqn201812078 to B.W.)

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