Attapulgite modified with covalent organic frameworks as the sorbent in dispersive solid phase extraction for the determination of pyrethroids in environmental water samples

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Attapulgite modified with covalent organic frameworks as the sorbent in dispersive solid phase extraction for the determination of pyrethroids in environmental water samples Chendi Jia Writing-original draftConceptualizationMethodologyInvestigationValidationVisualizationData Curation , Yiduo Mi Writing - review & editingFormal analysisMethodology , Zikai Liu Writing - review & editingFormal analysisMethodology , Wenfeng Zhou ResourcesMethodologyProject administration , Haixiang Gao ResourcesMethodologyProject administration , Sanbing Zhang ResourcesMethodologyProject administration , Runhua Lu ConceptualizationWriting - review & editingResourcesSupervisionFunding acquisition PII: DOI: Reference:

S0026-265X(19)32699-2 https://doi.org/10.1016/j.microc.2019.104522 MICROC 104522

To appear in:

Microchemical Journal

Received date: Revised date: Accepted date:

25 September 2019 6 December 2019 10 December 2019

Please cite this article as: Chendi Jia Writing-original draftConceptualizationMethodologyInvestigationValidationVisu Yiduo Mi Writing - review & editingFormal analysisMethodology , Zikai Liu Writing - review & editingFormal analysi Wenfeng Zhou ResourcesMethodologyProject administration , Haixiang Gao ResourcesMethodologyProject admin Sanbing Zhang ResourcesMethodologyProject administration , Runhua Lu ConceptualizationWriting - review & ed Attapulgite modified with covalent organic frameworks as the sorbent in dispersive solid phase extraction for the determination of pyrethroids in environmental water samples, Microchemical Journal (2019), doi: https://doi.org/10.1016/j.microc.2019.104522

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HIGHTLIGHTS 

The sorbent attapulgite grafted covalent organic frameworks was synthesized by a mild condition.

  

The parameters affecting the ATP@COFs-based DSPE were optimized. Rapid adsorption and desorption were obtained in this method. The method was successfully applied to extract pyrethroids in environmental water samples.

1

Attapulgite modified with covalent organic frameworks as the sorbent in dispersive solid phase extraction for the determination of pyrethroids in environmental water samples Authors: Chendi Jia, Yiduo Mi, Zikai Liu, Wenfeng Zhou, Haixiang Gao, Sanbing Zhang, Runhua Lu* Affiliations: Department of Applied Chemistry, China Agricultural University, Yuanmingyuan West Road #2, Haidian District, Beijing 100193, China Corresponding author: Runhua Lu

E-mail: [email protected]

2

Abstract A facile synthetic method of attapulgite@covalent organic frameworks was reported in this study. The composite was synthesized by covalently grafting covalent organic

frameworks

(synthesized

from

1,3,5-triformylphloroglucinol

and

p-phenylenediamine) onto attapulgite at room temperature and was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, zeta potential analysis, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy

and

Brunauer-Emmett-Teller

measurement.

The

synthesized

nanocomposite was used as a sorbent in dispersive solid phase extraction to extract pyrethroids from environmental water samples, and the parameters affecting the extraction efficiency were optimized. The linear range of the four pyrethroids was 2.5-500 μg L-1, and the enrichment factors ranged from 65.0 to 68.2. The method detection limits were between 0.83 and 1.79 μg L -1 under the optimal conditions. In addition, the intra-day and inter-day precision were 1.4%-4.8% and 2.7%-3.6%, respectively. Finally, the method was successfully applied to extract pyrethroids from real water samples with relative recoveries ranging from 71.2% to 88.7%. Keywords Attapulgite, Covalent organic frameworks, Dispersive solid phase extraction, Pyrethroids, Real water samples

3

1. Introduction Pyrethroids are a class of chemical synthetic insecticides based on the structure of pyrethrins, which are naturally present in chrysanthemums and have insecticidal activity [1]. Since pyrethroids were invented, they have been widely used in pest control because of their high efficiency, wide insecticidal spectrum and low toxicity to mammals [2]. However, with widespread application, pyrethroids will accumulate in the environment. Long-term exposure to pyrethroids can cause health hazards because pyrethroids are neurotoxic and will cause the destruction of sodium channels in axons. Some studies have shown that pyrethroids could also affect male reproductive function [3, 4]. Therefore, the detection of pyrethroids in the environment is of great significance. Because of the complexity of the sample matrix and the trace concentration of analytes, direct detection of pyrethroids with analytical instruments is very difficult. Therefore, sample pretreatment technology is indispensable. Through sample pretreatment, a sample can be purified and concentrated, and the interference can be reduced for subsequent instrumental analysis. Solid phase extraction (SPE) and liquid-liquid extraction (LLE) are two common methods. Compared with LLE, SPE has the advantages of simplicity, flexibility and the low consumption of organic solvents [5-7]. The basic principle of solid phase extraction is to transfer the analytes from the matrix to the active sites of the solid material [8]. Several materials have been applied as sorbents in SPE, including ion-imprinted polymer nanoparticles [9], porous carbons [10], multiwalled carbon nanotubes [11], etc. 4

Dispersive solid phase extraction (DSPE) was developed on the basis of the solid phase extraction method and was introduced by Anastasias et al. [12] In DSPE, sorbent materials are dispersed directly into the sample solution and fully contact with the analysts under the assistance of vortex or ultrasound [13-15]. The DSPE method has attracted wide attention in recent years due to its advantages of simple operation, high efficiency and no sorbent conditioning. DSPE also eliminates problems that may occur in traditional SPE, such as high pressure inside the SPE system or nanosorbent particles escaping from the cartridges [16-18]. The extraction efficiency in this method mainly depends on the properties of the sorbents, so the preparation of suitable sorbents is extremely important. Covalent organic frameworks (COFs) is a class of crystalline organic porous materials composed of small molecules connected by covalent bonds [19]. COFs have been widely applied in the fields of supercapacitor electrodes [20], gas separation [21], catalysis [22] and adsorption [23] owing to their high thermal stability, low density, large specific surface area, porosity and tunable pore size [24, 25]. However, compared with uses in other fields, the application of COFs in pesticide extraction is less common. The synthesis conditions of COFs are usually harsh, requiring a high temperature, inert gas protection and a long reaction time [26], which limit the further application of COFs in extraction fields. Therefore, the aim of this study is to establish a milder synthesis method and broaden the application of COFs in the field of pesticide extraction. Attapulgite (ATP), molecular formula [(OH2)4(Mg, Al, Fe)5(OH)·2Si8O20]·4H2O, is 5

a hydrated magnesium aluminum silicate clay mineral that commonly has a bedded structure, lath or fibrous morphology, and numerous features, such as a large specific surface area, stable physical and chemical properties and easy modification. More importantly, ATP is abundant in nature and cheap. These advantages give ATP great application potential and have caused ATP to attract widespread attention [27-29]. In addition, due to the high surface activity of raw ATP, it easily aggregates in solution, which is not conducive to dispersion [29]. Therefore, modifying ATP to improve its dispersion properties and extraction efficiency is necessary. In this study, covalent organic frameworks were grafted onto salinized attapulgite via covalent bonds and used as sorbents in the DSPE process of pyrethroids from real environmental water samples. The parameters that affect the extraction efficiency, such as the sorbent quantity, extraction time, salt concentration, pH, and desorption conditions, were optimized. 2. Experimental 2.1. Reagents and materials Sodium chloride (NaCl) and hydrochloric acid (HCl) were purchased from Beijing Chemical Factory (Beijing, China). Raw attapulgite (ATP) was purchased from Xuyi (Jiangsu, China). 3-Aminopropyltriethoxysilane (APTES), trifluoroacetic acid (TFA), phloroglucinol,

hexamethylenetetramine

and

p-phenylenediamine

(Pa)

were

purchased from Maya Reagent Corporation (Jiaxing, China). Dichloromethane, N,N-dimethylformamide (DMF), ethanol, acetone, hexane and ethyl acetate were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All 6

pyrethroid standards (cyhalothrin, bifenthrin, ethofenprox and fenpropathrin) (95%-97%) were purchased from Aladdin Reagent Corporation (Shanghai, China). HPLC-grade acetonitrile was obtained from Sigma-Aldrich LLC (USA). 2.2. Instrumentation and chromatographic conditions A vacuum drying oven (DZF-6050, Yiheng, Shanghai, China) was used to dry products. A TARGIN VX-III multitube vortexer (Beijing, China) was applied to automatically vortex samples. Quantitative analysis of pyrethroids was performed using an Agilent 1100 HPLC system (Agilent, USA) equipped with a DAD system. A Venusil XBP C18 analytical column (5 μm, 4.6 mm× 250 mm, Agela, China) and a Venusil C18 guard cartridge (5 μm, 4.6 mm × 10 mm, Agela, China) were applied for analyte separation. The mobile phase had a flow rate of 1 mL min-1 and consisted of a mixture of acetonitrile and water (77:23, v/v). The DAD detection wavelength was set at 220 nm, and the temperature of the column was kept at 25 °C. Fourier transform infrared (FT-IR) spectra (4000-400 cm−1) of the ATP, COFs and ATP@COFs were obtained by IRTracer-100 (Shimadzu, Japan). The texture of the ATP, COFs and ATP@COFs were observed by scanning electron microscopy (SEM) using a JEM-7800F instrument (JEOL, Tokyo, Japan). Transmission electron microscopy (TEM) imaging of ATP@COFs was performed on a JEM-2100F instrument (JEOL, Japan). X-ray diffraction (XRD) analysis was performed with an X’Pert PRO (PANalytical, Netherlands). The zeta potential was measured by a Zetasizer Nano-ZS90 (Malvern, UK). Brunauer-Emmett-Teller (BET) measurements were performed on an ASAP 2020 surface area and porosity analyzer (Micromeritics, 7

USA). X-ray photoelectron spectroscopy (XPS) was performed using a Kratos Axis Ultra DLD (Shimadzu, Japan). 2.3. Preparation of real environmental water samples The water samples were obtained from three different places (Miyun, Yanqi, and Changping) in Beijing, China, and stored in the dark at 4 °C. These environmental water samples were filtered through a 0.22 μm membrane before extraction. 2.4. Synthesis of 1,3,5-triformylphloroglucinol (Tp) The synthesis of Tp was performed according to a reported method [30, 31] with some modifications. A total of 45 mL of trifluoroacetic acid (TFA) was added to a 250 mL flask, and 7.55 g of hexamethylenetetramine was added in an ice bath with stirring. Then, the flask was removed from the ice bath, and 3 g of phloroglucinol was added under nitrogen atmosphere. The mixture was stirred at 100 °C for 2.5 h under N2, and then 75 mL of 3 mol L−1 hydrochloric acid was slowly added to the solution. The mixture was stirred continuously at 100 °C for another 1 h under N2. After cooling to room temperature, the mixture was filtered, and the filtrate was extracted with dichloromethane (50 mL×3). The organic phase was dried over magnesium sulfate and concentrated on a rotary evaporator to obtain Tp. 2.5. Synthesis of amino-functionalized ATP (ATP-NH2) First, raw ATP was activated and purified in hydrochloric acid (3 mol L−1) for 3 h, then filtered and washed with water until the filtrate was neutral. The ATP was dried at 60 °C for 8 h under vacuum to remove water. Then, 5.0 g of activated ATP and 150 mL of ethanol were added to a 500 mL flask and dispersed under ultrasonication for 8

30 min. Then, 5 mL of APTES was added, and the mixture was stirred under reflux at 80 °C for 10 h under nitrogen atmosphere, filtered, and washed with ethanol three times. The obtained ATP-NH2 was dried under vacuum overnight at 60 °C. 2.6. Preparation of ATP@COFs The synthesis steps of ATP@COFs are shown in Fig. S1a. ATP-NH2 (1.00 g) was added to a solution of 50 mL of ethanol containing Tp (315 mg, 1.5 mmol) and maintained at 50 °C for 1 h. Then, 50 mL of ethanol solution containing Pa (243 mg, 2.25 mmol) was added. The solution was reacted at room temperature for 30 min and washed with DMF and ethanol to obtain ATP@COFs [32]. The ATP@COFs were dried overnight at 60 °C under vacuum. To compare the extraction effect, COFs were synthesized by the same method without ATP-NH2. 2.7. Extraction procedure Fig. S1b demonstrates the DSPE procedure. A total of 10 mg of ATP@COFs and 8 mL of a water sample were added to a 10 mL centrifuge tube. The mixture was vortexed for 1 min to obtain full contact between the sorbent and the target analytes, followed by centrifuging (4500 rpm) for 5 min. The supernatant was removed, and the solid was dried under nitrogen stream at 50 °C. Then, 1000 μL acetonitrile was added with vortexing for 0.5 min. Half of the volume of the supernatant was transferred to another tube and evaporated to dryness at 45 °C under a nitrogen stream. Then, the residue was dissolved with 100 μL of acetonitrile. Finally, the solution was filtered with a 0.22 μm membrane, and 10 μL of the final solution was injected into the 9

HPLC-DAD system for detection. 2.8. Statistical analysis The enrichment factor (EF) for the target analytes was calculated using the following equation: EF=

Ce C0

where Ce is the final concentration of the analytes in the desorption solvent and C0 is the initial concentration of the analytes in the water sample solution. Ce was calculated from external calibration curves (Fig. S2) obtained by detecting different concentrations of standard solutions. The relative recovery (RR%) [33] was used for the analysis of real samples. The formula for RR% was as follows: RR (%) = (Cfound − Creal/Cadded) × 100 where Cfound is the detected concentration of the analyte after the addition of a known amount of standard to a real sample, Creal is the concentration of the analyte in the real sample, and Cadded is the concentration of the spiked known amount of standard in the real sample.

3. Results and discussion 3.1. Characterization of the materials SEM images of the ATP, COFs and ATP@COFs are shown in Fig. 1. As shown in Fig. 1 (a) and (b), ATP consists of randomly oriented rod-like fibers, and the COFs have a porous spherical structure. After modification with COFs, the surface of ATP 10

(Fig. 1c) becomes rough and is clearly covered with small particles, indicating that the COFs were grafted onto the ATP successfully. Furthermore, it can be observed from the TEM image of the ATP@COFs (Fig. 1d) that a lamellar structure appears between the rod fibers. The XRD patterns of ATP and ATP@COFs are shown in Fig. S3. The three characteristic peaks at 2θ=8.4° (110), 13.7° (200), and 16.3° (130) are attributed to ATP. The ATP@COFs composite exhibits the same characteristic diffraction peaks of ATP, which means that the crystal structure of ATP is not changed after modification by COFs. The ATP, COFs and ATP@COFs were characterized by FT-IR in the range of 4000 - 400 cm−1 (Fig. 2a). The characteristic peaks at 3553 cm−1 and 3422 cm−1 correspond to the stretching vibration bands of the -OH groups of ATP, and the peak at 1655 cm−1 is assigned to zeolite water. The peak at 1034 cm−1 is attributed to the stretching vibration of Si-O-Si groups [34]. The broad peak at 1611 cm−1 could be explained by the pooling of the C=O peaks and C=C peaks of COFs. The peak at 1441 cm−1 is attributed to aromatic C=C peaks, and that at 1254 cm−1 is attributed to the C=N characteristic stretching vibration band of COFs [30, 32]. Compared with the infrared spectrum of ATP, the ATP@COFs spectrum not only retains the characteristic absorption peaks of ATP but also presents new peaks at 1292 cm−1 and 1458 cm−1, which correspond to C=N and aromatic C=C groups, respectively. The above results indicate that COFs were successfully grafted onto ATP. The BET measurement of ATP and ATP@COFs was performed. As shown in Fig. 11

2b, the adsorption curve of the isotherm is not consistent with the desorption curve, indicating that the N2 adsorption-desorption isotherm (77 K) of ATP@COFs is a type IV curve with a type H3 hysteresis loop. Fig. 2c-d shows that the ATP@COFs have both mesoporous (3.36 nm) and microporous (0.57 nm) structures, which are derived from the structure of the COFs. The total pore volume of ATP@COFs is 0.50 cm3/g. The specific surface areas of ATP and ATP@COFs are 142 m2/g and 94 m2/g, respectively. The results indicate that grafting COFs onto ATP can reduce the surface activity of ATP, prevent its aggregation and facilitate dispersion [35]. The chemical composition of ATP@COFs was studied by XPS measurement (Fig. S4). From the wide-scan spectrum of ATP@COFs (Fig. S4a), silicon (103 eV, Si 2p; 154 eV, Si 2s), carbon (285 eV, C 1s), nitrogen (400 eV, N 1s), oxygen (532 eV, O 1s), and magnesium (1304 eV, Mg 1s) are obviously observed [36]. As shown in the high-resolution spectra of C 1s in Fig. S4b, the binding energy peaks at 284.7, 284.8, 286.1 and 288.5 eV are attributed to C-C/C-H, C=C, C-N and C=O, respectively. In the high-resolution spectrum of N 1s in Fig. S4c, the two peaks at 399.9 and 400.1 eV are assigned to N-H and C-N, respectively. The nitrogen-containing groups mainly originate from COFs; ATP does not contain nitrogen element or carbonyl groups. Therefore, the existence of N-H, C-N and C=O bonds indicates the successful preparation of ATP@COFs. The surface electrical characteristics of the ATP and ATP@COFs suspensions at different pH values were investigated by the zeta potential (Fig. S5). The isoelectric point (IEP) of ATP and ATP@COFs was approximately 2.6 and 3.3, respectively. 12

Moreover, the increase in zeta potential and shift in IEP toward higher pH of ATP@COFs illustrate that the COFs were successfully bonded to ATP. Moreover, the increase in zeta potential is conducive to the dispersion of ATP@COFs. 3.2. Optimization of ATP@COFs-DSPE conditions A dispersive solid phase extraction method based on ATP@COFs as an adsorption material was established and applied to the determination of pyrethroid pesticides in environmental water samples. The parameters affecting the extraction efficiency of the DSPE procedure were optimized to obtain a high extraction capacity. The standard stock solution of pyrethroids (cyhalothrin, bifenthrin, ethofenprox and fenpropathrin) at a concentration of 1000 mg L−1 was prepared by dissolving pyrethroids in acetonitrile and stored at 4 °C. The working standard solution was prepared by diluting the standard stock solution with acetonitrile. 3.2.1. Sorbent type For comparison, the extraction efficiency of the three solid materials (ATP, COFs and ATP@COFs) was studied. As observed in Fig. 3a, the recoveries of ATP and COFs were lower than 40%. The aggregation of ATP and COFs in solution [37] may affect their dispersion, resulting in poor contact with the analytes and thus affecting the extraction efficiency. However, the recoveries of ATP@COFs were higher than 80%. Grafting COFs onto ATP is beneficial to the dispersion of the sorbent in solution, and the recoveries are significantly improved. Therefore, ATP@COFs was finally selected as the sorbent in this experiment. 13

3.2.2. Amount of ATP@COFs The amount of solid sorbent is a key parameter affecting the extraction efficiency of pyrethroids. To study the effect of the amount of ATP@COFs, different amounts of ATP@COFs (5, 10, 15, 20, and 25 mg) were used during the DSPE procedure, and each sample was measured three times in parallel. As shown in Fig. 3b, increasing recoveries were obtained when the amount of the sorbent was increased from 5 mg to 10 mg. More active adsorption sites can be obtained as the sorbent quality increases, which is conducive to the increase of recoveries. At amounts of 15 mg or higher, the recoveries did not increase further, but decreased slightly. Therefore, 10 mg was chosen as the optimum amount of ATP@COFs in the following experiments. 3.2.3. Effect of extraction time The extraction process was carried out with the assistance of an automatic vortex instrument, and the time was set to 0.5, 1, 1.5, 2, or 2.5 min. It can be seen in Fig. 3c that extraction equilibrium was reached at 1 min and the recoveries were the highest. After 1 min, with increased extraction time, the recoveries decreased because the analytes may dissolve from the sorbent into the matrix. Therefore, in the following experiments, the extraction time was fixed at 1 min. 3.2.4. Effect of salt concentration and solution pH Different concentrations of NaCl were set in this experiment (0%, 2%, 4%, 6%, 8% and 10% (w/v)) to study the effect of ionic strength on extraction efficiency. Fig. 3d showed that the extraction efficiency of all pyrethroids declined with the addition of NaCl. The reason for this phenomenon may be that an increase in salt concentration 14

leads to an increase in solution viscosity, which is not conducive to the mass transfer of analytes to sorbent. After the sorbent is separated from the sample solution, NaCl is deposited on the surface of the sorbent, which may affect the subsequent desorption process. Therefore, no NaCl was added. pH plays an important role in the DSPE process because it may determine the existing form of the analytes and the charge species on the sorbent surface [38]. Different pH values ranging from 4 to 9 were investigated. As observed in Fig. S6, the overall recoveries did not change much in the selected pH range, so the pH was not adjusted in the following experiments. 3.2.5. Effect of desorption conditions Different desorption solvents have different action modes and dispersive properties with respect to the target analytes. Selecting suitable desorption solvents is also an important factor affecting the extraction efficiency. In this experiment, different desorption solvents (acetonitrile, ethanol, acetone, ethyl acetate and hexane) were selected (Fig. 3e). The ATP@COFs sorbent was agglomerated and could not be uniformly dispersed in hexane. Among the five desorption solvents, acetonitrile had the highest recoveries, so acetonitrile was chosen as the desorption solvent. Next, the effect of the acetonitrile volume in the range of 500-2500 μL was studied. As shown in Fig. S7, satisfactory recoveries were achieved with 1000 μL of acetonitrile. Further increases in volume would cause an unnecessary waste of acetonitrile without significantly changing the recoveries. The effect of desorption time was also studied by increasing the automatic vortex 15

time from 0.25 min to 2 min. The results (Fig. 3f) showed that 0.5 min was the optimum desorption time, meaning that desorption equilibrium was achieved quickly. Based on the above data, 1000 μL of acetonitrile with 0.5 min of vortex treatment was chosen as the optimum desorption conditions. 3.3. Method validation Under the optimized conditions, crucial analytical parameters were investigated to evaluate the method, such as the linearity, method detection limit (MDL), enrichment factor (EF), extraction recovery (ER), inter-day and intra-day precision, and so on. To validate these parameters, a series of spiked water samples with different concentrations (2.5, 5, 10, 25, 50, 100, 250, and 500 μg L-1) were analyzed, and each concentration was tested in four parallel replicates. The results were listed in Table 1. The linear range of the four pyrethroids was 2.5-500 μg L-1, with correlation coefficients (r) ranging from 0.9994 to 0.9997. The enrichment factors ranged from 65.0 to 68.2. The MDLs based on a signal-to-noise ratio of 3:1 (S/N=3) ranged from 0.83 to 1.79 μg L-1. Additionally, the absolute extraction recoveries (ER%) were in the range of 81.3–85.3%. The relative standard deviations (RSDs, n=4) of the intra-day and inter-day precision were detected for water solution spiked with pyrethroids on the same day and on four consecutive days. The intra-day RSDs were in the range of 1.4%-4.8%, and the inter-day RSDs were between 2.7% and 3.6%. 3.4. Reusability of sorbent To assess the reusability of the ATP@COFs, the used sorbents were washed with acetonitrile three times and then dried overnight under vacuum at 60 °C. As shown in 16

Fig. S8, the recoveries of fenpropathrin, cyhalothrin and ethofenprox did not decrease significantly within five times, but with increasing recycling times, the recovery of bifenthrin decreased gradually but remained over 75%. Therefore, the ATP@COFs have good reusability and can be reused five times. 3.5. Adsorption mechanism According to the structure of ATP@COFs (which have amino groups), hydrogen bond interactions may exist between ATP@COFs and pyrethroids. Further study was conducted by adding pyrethroids at 50 μg L-1 to water samples containing some amount of ATP@COFs. After filtration, the sorbent was dried under nitrogen stream at 50 °C. The FT-IR spectra of ATP@COFs before and after adsorption (Fig. S9) were compared. The ATP@COFs exhibited obvious N-H (3553 cm−1) stretching vibrations. After the adsorption of pyrethroids, this peak moved to 3547 cm−1, showing a redshift to some extent, indicating that there were hydrogen-bond interactions between the ATP@COFs and pyrethroids. According to the reported literature [31], we speculated that π-π stacking interactions and hydrophobic interactions may also exist. 3.6. Application to real water samples To evaluate the applicability of the ATP@COFs-based DSPE method, pyrethroids in river water samples from three different locations in Beijing were determined. No pyrethroids were detected in these water samples. The relative recoveries of the analytes were evaluated by analyzing spiked water samples at concentrations of 10, 50 and 100 μg L-1 in quadruplicate (Table 2). The relative recoveries ranged from 71.2% to 88.7%, and RSDs were found to be within 0.7% to 8.7%. Typical chromatograms 17

of blank and spiked water samples are given in Fig. S10. The

matrix effects

were

evaluated

by calculating

the

percent

signal

suppression/enhancement obtained via the extraction process for three water samples. The slope ratios of the spiked blank water sample extracts were compared with those of the corresponding spiked solvent (mobile phase) at the same concentration level [39, 40]. The matrix effect values ranged from 96.1% to 103.8%, which demonstrated that there were very few matrix effects present. 3.7. Comparison of ATP@COFs-DSPE with other reported methods To evaluate the advantages of ATP@COFs-DSPE, a comparison of several important parameters in this work and previous methods is summarized in Table 3 [41-45]. The extraction equilibrium time (1 min) of this method is less than those of other methods. Moreover, the ATP@COFs-DSPE method has a lower RSD and required

sorbent

amount.

The

comparative

results

indicate

that

the

ATP@COFs-DSPE method is quick and effective with satisfactory precision. 4. Conclusion In this study, COFs was successfully grafted onto attapulgite, and ATP@COFs were applied as a sorbent in dispersive solid phase extraction combined with high performance liquid chromatography to detect pyrethroids in real water samples. Raw ATP is abundant and cheap in nature, and the grafting reaction with COFs has the advantages of mild synthesis conditions, a short time requirement (1.5 h) and simple operation, which are conducive to further application. Moreover, the reduced amount of organic solvent required, rapid adsorption and desorption, good linearity, 18

satisfactory recoveries and reusability make ATP@COFs an excellent sorbent for DSPE technology. Therefore, ATP@COFs can be a good choice for extracting pyrethroids in environmental water samples. To expand the application of this method to more complex matrixes, the ATP@COFs-DSPE method may be combined with more sensitive detection methods, such as mass spectrometry, in subsequent experiments. Acknowledgments This work was supported by the National Natural Science Foundation of China (Project No. 21677174, 21277172).

Author contributions All the authors discussed the proposal and plan of this review. Chendi Jia: Writing-original draft, Conceptualization, Methodology, Investigation, Validation, Visualization, Data Curation. Yiduo Mi, Zikai Liu: Writing - review & editing, Formal analysis, Methodology. Wenfeng Zhou, Haixiang Gao, Sanbing Zhang: Resources, Methodology, Project administration. Runhua Lu*:Conceptualization, Writing - review & editing, Resources, Supervision, Funding acquisition.

Conflict of interest The authors have declared no conflict of interest.

19

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28

Captions

Fig.1. SEM images of (a) ATP, (b) COFs, (c) ATP@COFs and TEM image of (d) ATP@COFs.

29

Fig.2. (a) FT-IR spectra, (b) N2 adsorption-desorption isotherm, (c) mesopore distribution and (d) micropore distribution of ATP@COFs.

30

Fig.3. The effect of (a) sorbent type, (b) the amount of ATP@COFs, (c) extraction time, (d) NaCl concentration, (e) desorption solvent and (f) desorption time on the extraction efficiency.

31

Table 1. Analytical parameters of DSPE with ATP@COFs Analyte Fenpropathrin Cyhalothrin Ethofenprox Bifenthrin

Linear equation y = 1.5419x + 3.6323 y = 1.8634x + 11.495 y = 1.6158x + 17.13 y = 2.138x + 1.1064

Linear range (μg L-1)

r

2.5-500 2.5-500 2.5-500 2.5-500

0.9996 0.9994 0.9994 0.9997

MDL (μg L-1)

EF

1.01 1.19 0.83 1.79

68.2 67.2 67.3 65.0

32

ER (%) 85.3 84.0 84.2 81.3

RSD (%) Intra-day 5 (μg L-1)

50 (μg L-1)

250 (μg L-1)

3.7 4.2 3.6 4.8

2.5 1.9 3.1 4.1

1.4 3.7 1.9 4.6

Inter-day 2.7 3.6 3.1 3.2

Table 2. Results of the determination of pyrethroids in real water samples (n=4).

Analyte

Fenpropathrin

Cyhalothrin

Ethofenprox

Bifenthrin

Spiked level （μg L-1）

River water 1

River water 2

RSD（%）

RR （%）

Intra-day

10

77.5

50

River water 3

RSD（%）

Inter-day

RR （%）

Intra-day

6.9

6.4

86.2

77.1

4.3

5.7

100 10 50 100 10 50 100 10

72.3 80.6 82.4 84.7 84.6 88.7 83.5 77.7

2.4 4.2 0.7 1.0 2.2 7.0 3.8 4.3

50

79.7

100

84.4

RSD（%）

Inter-day

RR （%）

Intra-day

Inter-day

0.8

7.9

78.5

8.5

6.1

82.2

3.6

3.9

80.4

4.0

2.9

7.9 4.4 1.8 5.6 8.7 6.3 3.9 6.0

76.6 78.8 87.0 82.1 85.2 82.3 84.7 86.0

1.9 5.0 5.8 3.5 7.8 2.2 2.5 5.7

6.1 6.6 6.1 2.4 8.0 5.9 2.9 7.6

71.2 83.5 86.8 78.2 82.9 85.9 83.0 79.5

3.2 5.4 1.2 2.9 4.6 4.8 2.1 8.5

5.1 4.1 6.1 2.2 6.9 3.5 2.4 6.5

6.7

5.5

80.4

4.6

5.7

79.2

5.2

6.4

4.7

5.3

82.9

2.8

2.9

80.3

3.8

2.0

33

Table 3. Comparison of the methods for pyrethroids determination in water Method a

ME-SFO-LPME DLME/D-μ-SPE UA-DLLMEc DLLME MSPEe DSPE

Extraction material

Detection system

Sorbent amount

Extraction time

RSD (%)

MDL (μg L-1)

Ref.

1-dodecanol 1-Octanol and APTSb DES [C6MIM][PF6]d CoFe2O4/PGCf ATP@COFs

HPLC-UVD HPLC-UV HPLC-UVD HPLC-UV HPLC-DAD HPLC-DAD

60 μL 10 mg 30 mg 46 μL 40 mg 10 mg

10 min 6 min 3 min 5 min 10 min 1 min

1.7-2.2 1.8-2.5 1.45-4.86 3.9-10.1 0.2-5.8 1.4-4.8

0.37-0.75 0.05–2.0 0.30–0.60 0.94-1.97 0.18-0.31 0.83-1.79

[41] [42] [43] [44] [45] Present work

a

membrane emulsification-liquid phase microextraction based on solidification of organic droplets 3-aminopropyl triethoxysilane c ultrasound-assisted dispersive liquid-liquid microextraction d 1-hexyl-3-methylimidazolium hexafluorophosphate. e magnetic solid phase extraction f CoFe2O4-embedded porous graphitic carbon b

34