A method for simultaneously detecting six trace herbicides in water

Abstract

The present invention discloses a method for simultaneously detecting six trace herbicides in water. The method loads ionic liquid into COF material and uses it as an adsorbent for solid phase extraction to enrich the six herbicides in the water sample. The method specifically includes the following steps: 1) synthesis of COF; 2) synthesis of IL@COF; 3) collection of water sample; 4) preparation of SPE column; 5) activation and pre-equilibrium; 6) sample spectrum; 7) establishment of standard curve; 8) analysis of detection results. The present invention adopts solid phase microextraction technology to pre-concentrate trace herbicides in water samples, and designs and synthesizes a IL@COF to replace the traditional solid phase material as an extractant. The new IL@COF extraction material has a large pore surface area, strong specific adsorption capacity, can be reused for more than 10 times, integrates concentration and extraction, and has the advantages of simple and convenient operation, short extraction time, high extraction efficiency, safety and environmental protection, and small amount of extractant and sample.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental analysis and detection, and specifically relates to a method for simultaneously detecting six trace herbicides in water. Background Art

[0002] With the development of modern agriculture, herbicides have been widely used in agricultural production. Although the commonly used herbicides in agricultural production have the characteristics of low toxicity and short half-life, their large amount and high frequency of use lead to their "persistent" existence in the environment. Therefore, herbicide pollutants have become one of the most common organic pollutants in the world. Although herbicides are usually sprayed in the air, aquatic ecosystems can be exposed to herbicides through runoff or spray drift, accidental leakage, etc.; secondly, rain washing can also cause herbicides to enter the groundwater environment through soil faults. Most importantly, most herbicides exist in the form of ions and are easy to transfer. Herbicides that enter the water are accumulated in the water environment through a series of transformations, and finally enter the organism through bioaccumulation under the influence of the food chain. Considering the above facts, the detection and quantitative analysis of herbicide residues in water bodies are of great significance.

[0003] So far, a variety of sample preparation methods have been used for pesticide analysis, among which solid phase extraction, solid phase microextraction and liquid-liquid extraction are the most commonly used pesticide pretreatment methods and technologies. In recent years, separation and enrichment technology has developed towards simplification, miniaturization, and minimization of organic reagent consumption. Among them, solid-liquid microextraction has shown a high sample extraction capacity and good enrichment effect, and is simple and fast. However, the selection of the stationary phase in this method is one of the most critical factors. Covalent organic framework (COF) materials have mesoporous or microporous structures, high specific surface area and porosity, and excellent physical and chemical stability, which also make them suitable as enrichment media for sample pretreatment and can separate trace targets from complex matrices. Ionic liquids (ILs) are a new type of ionic compounds composed entirely of anions and cations, which are liquid at room temperature. They are almost non-volatile, have designable structures and properties, and are stable. In particular, by adjusting the anion and cation types and functional group structures of ionic liquids, ionic liquids can be endowed with strong hydrogen bonding, π-π and other specific interaction capabilities, significantly improving the selective recognition ability of the extraction medium for structurally similar solutes, and obtaining an efficiency superior to that of traditional separation methods. However, there have been no reports on the use of composite materials of ionic liquids and covalent organic frameworks in the detection of trace herbicides in water. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a technical solution for a method for simultaneously detecting six trace herbicides in water. The present invention uses a simple and mild room temperature method to design and prepare a new type of covalent organic framework material loaded with ionic liquid for the first time, and uses it as an adsorbent to make a homemade solid phase extraction column for extracting six herbicides in water samples. Through HPLC-UV detection, ultra-sensitive determination of six herbicides and pesticides in water is achieved. Compared with other detection methods, the amount of organic solvent used in the present invention is greatly reduced, and the detection is more sensitive.

[0005] The present invention is specifically implemented through the following technical solutions:

[0006] A method for simultaneously detecting six trace herbicides in water, wherein the ionic liquid is loaded into a COF material and used as an adsorbent for solid phase extraction to enrich the six herbicides in the water sample, and specifically comprises the following steps:

[0007] 1) Synthesis of COF: Weigh 1,3,5-tris(4-aminophenyl)benzene and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde into a 50 ml centrifuge tube, add mesitylene and 1,4-dioxane solution, add 3M acetic acid dropwise after ultrasonic dispersion, and react by shaking at room temperature. After the reaction, filter and collect the red-brown precipitate, wash it three times with anhydrous methanol to remove impurities, and finally place the washed material in a vacuum drying oven and dry it at 60°C for 12 hours to obtain COF material;

[0008] 2) Synthesis of IL@COF: Weigh the ionic liquid and 1,4-dioxane solution and place them in a 50mL centrifuge tube, add 2mL 1,4-dioxane and 2mL mesitylene, and after ultrasonic dispersion for 10min, add 1mL 3M acetic acid dropwise, and ultrasonically react for 10min to obtain a mixed solution; disperse a certain amount of 1,3,5-tris(4-aminophenyl)benzene in 2mL 1,4-dioxane and 2ml mesitylene to obtain a mixture, add the mixture to the above mixed solution, and oscillate at room temperature for 20min. After the reaction, filter and collect the reddish-brown precipitate, and wash it with anhydrous methanol 3 times to remove impurities. Finally, place the washed material in a vacuum drying oven and dry it at 60°C for 12h to obtain IL@COF material;

[0009] 3) Collect water samples: After removing impurities in the water sample by vacuum filtration, filter it with a 0.45 μm aqueous phase filter membrane, adjust the pH of the water sample with hydrochloric acid or sodium hydroxide, and store it in a refrigerator at 4°C for later use;

[0010] 4) Preparation of SPE columns: Self-assemble the SPE columns of IL@COF materials using 1 mL SPE empty column tubes and polypropylene gaskets: First, put a polypropylene gasket into the empty column tube, then load the IL@COF material, flick the tube wall by hand to make the material evenly distributed in the column tube, and finally place another polypropylene gasket on top of the material to compact the IL@COF material so that the filling material remains at the bottom of the SPE tube to prepare the SPE column;

[0011] 5) Activation and pre-equilibration: The SPE column prepared in step 4) is rinsed with 3 mL of methanol and 3 mL of ultrapure water, respectively, to activate and pre-equilibrate the column;

[0012] 6) Sample spectrum: Add the water sample obtained in step 3) to the activated SPE column in step 5). After the loading is completed, place the extraction column at a certain temperature for several minutes, then rinse the column with 3-6 mL ultrapure water, then desorb with 2-6 mL methanol, and then blow dry the desorbed liquid with nitrogen at 40°C. Finally, re-dissolve with 1 mL methanol solution, sonicate for 5 minutes, filter the re-dissolved solution with a 0.22 μm microporous filter membrane and store it in a sample bottle for high performance liquid chromatography analysis to obtain a sample spectrum;

[0013] 7) Establishing a standard curve: weighing standard substances of Pro, Met, Btz, Iso, Ace, and But, preparing single standard stock solutions with methanol or acetonitrile as solvent, and then preparing mixed standard working solutions as needed, testing the obtained mixed standard solution under the high performance liquid chromatography analysis conditions in step 6) to obtain a standard substance spectrum, and drawing standard curves of Pro, Met, Btz, Iso, Ace, and But respectively, with the injection concentration of each standard substance in the mixed standard solution as the abscissa x and the peak area of ​​the corresponding standard substance in the standard substance spectrum as the ordinate y;

[0014] 8) Analysis of test results: The peak area values ​​of each herbicide component in the sample spectrum obtained in step 6) are respectively substituted into the corresponding standard curve obtained in step 7), and the content of the herbicide component in the sample is obtained by calculation.

[0015] Furthermore, the six herbicides are promethazine, metribuzin, bentazon, isoproturon, setochlor and butachlor.

[0016] Further, in step 1), the amount of 1,3,5-tris(4-aminophenyl)benzene is 100-120 mg, preferably 112 mg, the amount of 2,5-dimethoxybenzene-1,4-dicarbaldehyde is 80-100 mg, preferably 93 mg, the amount of mesitylene and 1,4-dioxane solution added is 3 mL, the amount of acetic acid added is 1 mL, the ultrasonic dispersion time is 30 min, and the room temperature shaking reaction time is 20 min.

[0017] Furthermore, in step 2), the ionic liquid is any one of 1-decyl-3-methyl imidazole bromide, decylmethyl imidazole chloride, and 1-octyl-3-methyl imidazole bromide, preferably decylmethyl imidazole chloride.

[0018] Further, in step 2), the amount of ionic liquid used is 40-250 mg, preferably 140 mg, the amount of 1,3,5-tris(4-aminophenyl)benzene used is 100-120 mg, preferably 112 mg, and the amount of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde used is 80-100 mg, preferably 93 mg.

[0019] Furthermore, in step 3), the pH of the water sample is 4-8, preferably pH 5.

[0020] Furthermore, in step 4), the IL@COF material used is 2-20 mg, preferably 12 mg.

[0021] Furthermore, in step 6), the amount of water sample is 0.5-1 mL, preferably 1 mL; the certain temperature is 20-40°C, preferably 25°C, and the standing time is 10-30 min, preferably 30 min.

[0022] Further, the conditions for high performance liquid chromatography analysis in step 6) and step 7) are: Shimadzu liquid chromatograph, including LC-20AD separation chromatography system, SIL-20A automatic injection system, CTO-20A column oven, SPD-20A UV / visible detector, chromatographic column Waters XSelect TM HSS T3 (4.6mm×250mm, 5μm), with acetonitrile as mobile phase A and 0.1% phosphoric acid as mobile phase B, gradient elution: 0-15min 35% A; 15-25min 35→45% A; 25-30min 45→90% A; 30-40min 90% A; detection wavelength was 210nm; column temperature was 35℃, and injection volume was 20μL.

[0023] The present invention adopts solid phase microextraction technology to pre-concentrate trace herbicides in water samples, and designs and synthesizes an IL@COF to replace traditional solid phase materials as an extractant. The new IL@COF extraction material has a pore surface area and strong specific adsorption capacity. It can be reused for more than 10 times, integrates concentration and extraction, and has the advantages of simple and convenient operation, short extraction time, high extraction efficiency, safety and environmental protection, and small amounts of extractant and sample.

[0024] At present, herbicide pollution has become an important research topic in environmental protection, and its detection and removal are the primary goals. The present invention uses IL@COF new extraction material as a solid phase extractant, which has the advantages of low cost, safety and non-toxicity. At the same time, IL@COF has the advantage of being reusable many times, which greatly reduces the cost of removing and detecting trace herbicides in water. It is also easy to operate and requires a small amount of herbicide, so it has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Liquid phase diagram of six herbicide standards;

[0026] Figure 2 Liquid phase diagram of herbicide samples;

[0027] Figure 3 Synthesized COF and IL@COF materials;

[0028] Figure 4 Characterization diagram of COF and IL@COF materials;

[0029] Figure 5 Effects of COF and IL@COF on herbicide extraction;

[0030] Figure 6 Effects of extraction agent dosage, different temperatures, time and pH on extraction effect;

[0031] Figure 7 The impact of IL@COF reuse on extraction effect;

[0032] Figure 8 This method is used for actual water sample extraction. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with specific embodiments to facilitate a better understanding of the present technical solution.

[0034] Example 1: A method for simultaneously detecting six trace herbicides in water

[0035] 1) Synthesis of COF: Weigh 112 mg of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 93 mg of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTA) in a 50 ml centrifuge tube, add 3 ml of mesitylene and 3 ml of 1,4-dioxane solution, ultrasonically disperse for 30 min, then add 1 mL of 3M acetic acid dropwise, shake at room temperature for 20 min, filter and collect the reddish brown precipitate after the reaction, and wash it 3 times with anhydrous methanol to remove impurities. Finally, place the washed material in a vacuum drying oven and dry it at 60 ° C for 12 h to obtain COF material;

[0036] 2) Synthesis of IL@COF: In a 50mL centrifuge tube, weigh 140mg of decylmethylimidazole chloride and 93mg of DMTA, add 2mL of 1,4-dioxane and 2mL of mesitylene, and after ultrasonic dispersion for 10min, add 1mL of 3M acetic acid dropwise and react by ultrasonication for 10min. Weigh 112mg of TAPB and disperse it in 2mL of 1,4-dioxane and 2ml of mesitylene, add the mixture to the above solution, and react by shaking at room temperature for 20min. After the reaction is completed, filter and collect the reddish-brown precipitate, and wash it 3 times with anhydrous methanol to remove impurities. Finally, the washed material is placed in a vacuum drying oven and dried at 60°C for 12h to obtain the IL@COF material; pictures of the synthesized COF and IL@COF materials are shown in the figure. Figure 3 As shown; the characterization diagram of COF and IL@COF materials is shown Figure 4 The effects of COF and IL@COF on herbicide extraction are shown in Figure 5 shown.

[0037] 3) Collect water samples, remove impurities in the water samples by vacuum filtration, filter them with a 0.45 μm aqueous phase filter membrane, adjust the pH of the water samples to 5.0 with hydrochloric acid or sodium hydroxide, and store them in a refrigerator at 4°C for later use;

[0038] 4) Self-assemble the SPE column of IL@COF material using 1mL SPE empty column tube and polypropylene gasket. First, put a polypropylene gasket into the empty column tube, then load 12mg of the synthesized IL@COF or COF material, flick the tube wall by hand to make the material evenly distributed in the column tube, and finally place another polypropylene gasket on top of the material to compact the IL@COF / COF material to keep the filling material at the bottom of the SPE tube;

[0039] 5) First, rinse the SPE column prepared in step 4) with 3 mL of methanol and 3 mL of ultrapure water respectively to activate it;

[0040] 6) Add 1 mL of the water sample obtained in step 3) to the SPE column activated in step 5). After loading, place the extraction column at 25°C for several minutes. Then, rinse the column with 3-6 mL of ultrapure water, desorb with 2-6 mL of methanol, and blow dry the desorbed solution with nitrogen at 40°C. Finally, re-dissolve with 1 mL of methanol solution, sonicate for 5 minutes, filter the re-solution with a 0.22 μm microporous filter membrane and store it in a sample bottle for high-performance liquid chromatography analysis to obtain a sample spectrum;

[0041] 7) Establishment of standard curve: weigh the standard substances of Pro, Met, Btz, Iso, Ace, and But, prepare a single standard stock solution with methanol or acetonitrile as solvent, and then prepare a mixed standard working solution as needed. The obtained mixed standard solution is tested under the high performance liquid chromatography analysis conditions in step 6) to obtain a standard substance spectrum. The liquid phase diagram of the six herbicide standards is as follows: Figure 1 As shown, the liquid phase diagram of the herbicide sample is as follows Figure 2 As shown, with the injection concentration of each standard substance in the mixed standard solution as the abscissa x and the peak area of ​​the corresponding standard substance in the standard substance spectrum as the ordinate y, the standard curves of Pro, Met, Btz, Iso, Ace, and But are drawn respectively;

[0042] 5) Analysis of test results: The peak area values ​​of each herbicide component in the sample spectrum obtained in step 6) are respectively substituted into the corresponding standard curve obtained in step 7), and the content of the herbicide component in the sample is obtained by calculation.

[0043] The conditions for the high performance liquid chromatography analysis in step 6) and step 7) are as follows: Shimadzu liquid chromatograph, including LC-20AD separation chromatography system, SIL-20A automatic injection system, CTO-20A column oven, SPD-20A UV / visible detector, chromatographic column Waters XSelect TM HSS T3 (4.6 mm × 250 mm, 5 μm), with acetonitrile as mobile phase A and 0.1% phosphoric acid as mobile phase B, gradient elution: 0-15 min, 35% A; 15-25 min, 35→45% A; 25-30 min, 45→90% A; 30-40 min, 90% A. Detection wavelength was 210 nm; column temperature was 35 ° C, injection volume was 20 μL;

[0044] Example 2: Optimization and verification of method conditions for simultaneous detection of six trace herbicides in water

[0045] Detection instrument: Shimadzu high performance liquid chromatograph, including separation chromatography system (LC-20AD), automatic sampling system (SIL-20A), column chamber (CTO-20A) and UV / visible detector (SPD-20A).

[0046] Preparation and characterization of COF / IL@COF: The morphology of COF and IL@COF composites was characterized by field emission scanning electron microscopy (SEM) and field emission transmission electron microscopy (TEM).

[0047] Sample treatment: 50 mL of the collected water sample was centrifuged at 4000 rpm for 10 min. The supernatant was filtered through a 0.45 μm filter membrane to obtain a water sample. The pH was adjusted to 5.0 and stored in a refrigerator at 4°C for use.

[0048] Extraction process: First, the SPE column filled with 12 mg IL@COF or COF was activated. After activation in the centrifuge tube, 1.0 mL of water sample was added and allowed to stand at 25°C for 30 min. Subsequently, the column was rinsed with 3-6 mL of ultrapure water, and then desorbed with 2-6 mL of methanol. The desorbed solution was then dried with nitrogen at 40°C. Finally, it was re-dissolved with 1 mL of methanol solution, and after ultrasonication for 5 min, the re-solution was filtered with a 0.22 μm microporous filter membrane and stored in a sample bottle for HPLC analysis.

[0049] HPLC determination: The following chromatographic conditions were used to determine the peak areas of the six herbicides to be tested, and the contents of BTZ, PSE, ALF, FPE, and PBZ were obtained by substituting the standard working curve equation (Table 1). Chromatographic conditions: Chromatographic column: WondaCract ODS-2 column (5μm, 250×4.6mm); acetonitrile was used as mobile phase A, 0.1% phosphoric acid was used as mobile phase B, and gradient elution was performed: 0-15min, 35% A; 15-25min, 35→45% A; 25-30min, 45→90% A; 30-40min, 90% A. The detection wavelength was 210nm; the column temperature was 35°C, and the injection volume was 20μL;

[0050] Results and Analysis

[0051] Optimization of extraction conditions: In order to obtain higher extraction efficiency, IL@COF solid phase extraction was used to extract water samples containing herbicides, including Pro, Met, Btz, Iso, Ace, and But, and the effects of different extraction parameters on the recovery of herbicides in water samples were studied. Therefore, in order to establish a solid-liquid microextraction method for herbicide extraction using IL@COF solid phase, the parameters controlling performance, such as solid-liquid ratio, temperature, time, and pH optimization, were investigated.

[0052] IL@COF: Investigation of solid-liquid ratio of water extraction

[0053] The selection of extractant is crucial in the process of liquid phase microextraction. A good extractant can often effectively extract the analyte from a large amount of matrix with a small amount, achieving the purpose of separation and enrichment simultaneously. The present invention conducted experiments with solid-liquid ratios of 3:1, 5:1, 8:1, 10:1, 12:1, 15:1 and 18:1 (mg / mL). Figure 6 aIt can be seen that when the solid-liquid ratio is 12:1, the extraction recovery rate reaches the maximum, so it is selected for the next experiment.

[0054] Extraction temperature investigation: Temperature has a certain influence on the extraction efficiency. This study conducted experiments on the extraction efficiency in the temperature range of 20-45℃. Figure 6b It can be seen that when the extraction temperature is 25 °C, the extraction recovery rate reaches the maximum, so the solid-liquid ratio of 12:1 and the extraction temperature of 25 °C are selected for the next experiment.

[0055] Extraction time investigation: In solid-liquid microextraction research, extraction time is also a key factor affecting extraction efficiency. This study studies the extraction efficiency of 2-30 min. Figure 6 c It can be seen that the extraction recovery rate basically reaches 100% at 30 minutes, that is, the herbicide in the water is completely extracted, so the extraction time is selected as 30 minutes.

[0056] Extraction pH investigation: pH is an important parameter that affects the ionic form of herbicides. Figure 6 dIt can be seen that the extraction recovery rate is the highest at pH 5, so the extraction pH is selected as 5.

[0057] Material reuse research: Material reuse is an important indicator for evaluating the quality of materials. Figure 7 It can be seen that after IL@COF was reused 10 times, the herbicide recovery rate, except for Btz, could still reach about 100%.

[0058] Analytical method validation: After the above experimental optimization, the analytical methodology of the six pesticides was further validated, including linear range, limit of detection (LOD), limit of quantification (LOQ), sample recovery rate, etc. According to the test results, the peak area (Y) was compared with the herbicide concentration (x, μg L -1 ) were plotted into a linear regression curve, and the linear regression equation was shown in Table 1. The six pesticides showed a good linear relationship (r2≥0.9998) in the detection range of 500-20000μg / L. The signal-to-noise ratio (S / N) of 3 and 10 were used as the detection limit (LOD) and quantification limit (LOQ), respectively, and the LODs of the six pesticides were 14.5-47.0μg / L and LOQs were 47.0-128.1μg / L.

[0059] Under the optimal conditions, three concentration levels of standard solutions were added to the sample, 1000, 2000, and 3000 μg / L, and three solid phase extraction processes were performed with each sample spike solution at different concentrations. The extracts obtained in each process were analyzed by HPLC. The RSD (n=3) of the six herbicides was calculated to be between 0.996-9.699%; the spike recovery was between 85-125% (Table 1), indicating that the method has good accuracy.

[0060] Table 1 Standard curve equation, linear correlation coefficient, linear range, detection limit (LOD), quantification limit (LOQ), and recovery rate of each component

[0061]

[0062]

[0063] In addition, six ultrapure samples containing mixed standards were processed by the established solid phase extraction method and tested on the instrument to evaluate the precision of the method by intra-day RSD and inter-day RSD. The intra-day and inter-day RSD ranged from 0.05 to 6.52%, indicating that the method has good precision.

[0064] Real sample analysis: The above IL@COF solid-liquid microextraction combined with HPLC analysis method was used to analyze 10 different environmental water samples (using the optimal method of Example 1) to further evaluate the applicability and reliability of this method. Figure 8 As shown, butachlor (But) was detected in the highest amount in the 10 water samples, followed by bentazon (But), acetochlor (Ace) and metribuzin (Met).

[0065] The present invention proposes an analytical method for preparing six herbicide-specific SPE columns using the IL@COF novel material, and combining it with HPLC to simultaneously detect the trace contents of six herbicides, namely, Pro, Met, Btz, Iso, Ace, and But, in water samples. The IL@COF novel material can be reused more than 10 times, and the herbicide recovery rate can still reach more than 100%, indicating that the material has excellent stability, realizes the one-step operation of extraction and purification in sample pretreatment, and reduces the interference of the water sample matrix. The experimental results of the accuracy, precision, linear range, detection limit, etc. of this method show that this method can be used for the analysis of actual samples such as water. Compared with the national standard method, the method greatly reduces the consumption of organic reagents, is more economical and environmentally friendly, and provides important reference and technical support for the research and analysis of environmental pesticide residues.

Claims

1. A method for simultaneously detecting six trace herbicides in water, characterized in that: The method loads ionic liquid into COF material and uses it as an adsorbent for solid phase extraction to enrich six herbicides in water samples. The method specifically includes the following steps: 1) Synthesis of IL@COF: Weigh the ionic liquid and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde into a 50 mL centrifuge tube, add 2 mL 1,4-dioxane and 2 mL mesitylene, and ultrasonically disperse for 10 min. Then, add 1 mL 3M acetic acid dropwise, and ultrasonically react for 10 min to obtain a mixed solution. A certain amount of 1,3,5-tris(4-aminophenyl)benzene is dispersed in 2 mL 1,4-dioxane and 2 ml mesitylene to obtain a mixture, and the mixture is added to the above mixed solution. The mixture is shaken and reacted at room temperature for 20 min. After the reaction is completed, the red-brown precipitate is collected by filtration and washed with anhydrous methanol for 3 times to remove impurities. Finally, the washed material is placed in a vacuum drying oven and dried at 60°C for 12 h to obtain the IL@COF material, wherein the ionic liquid is any one of 1-decyl-3-methylimidazole bromide, decylmethylimidazole chloride, and 1-octyl-3-methylimidazole bromide. 2) Collect water samples: After removing impurities from the water sample by vacuum filtration, filter it with a 0.45 μm aqueous phase filter membrane, adjust the pH of the water sample with hydrochloric acid or sodium hydroxide, and store it in a refrigerator at 4 ℃ for later use; 3) Preparation of SPE columns: Self-assemble the SPE columns of IL@COF materials using 1 mL SPE empty column tubes and polypropylene gaskets: First, put a polypropylene gasket into the empty column tube, then load the IL@COF material, and flick the tube wall by hand to make the material evenly distributed in the column tube. Finally, place another polypropylene gasket on top of the material to compact the IL@COF material and keep the filling material at the bottom of the SPE tube to obtain the SPE column; 4) Activation and pre-equilibration: Rinse the SPE column prepared in step 3) with 3 mL of methanol and 3 mL of ultrapure water, respectively, to activate and pre-equilibrate it; 5) Sample spectrum: Add the water sample obtained in step 2) to the activated SPE column in step 4). After the loading is completed, place the extraction column at a certain temperature for several minutes. Then, rinse the column with 3-6 mL of ultrapure water, then desorb with 2-6 mL of methanol, and then blow dry the desorbed liquid with nitrogen at 40°C. Finally, re-dissolve it with 1 mL of methanol solution, sonicate for 5 minutes, filter the re-dissolved solution with a 0.22µm microporous filter membrane and store it in a sample bottle for high performance liquid chromatography analysis to obtain the sample spectrum; 6) Establishment of standard curve: weigh the standard substances of promethazine, metribuzin, bentazon, isoproturon, acetochlor and butachlor, prepare single standard stock solutions with methanol or acetonitrile as solvent, and then prepare mixed standard working solutions as needed, and test the obtained mixed standard solution under the high performance liquid chromatography analysis conditions in step 5) to obtain a standard substance spectrum, and draw standard curves of promethazine, metribuzin, bentazon, isoproturon, acetochlor and butachlor respectively, with the injection concentration of each standard substance in the mixed standard solution as the abscissa x and the peak area of ​​the corresponding standard substance in the standard substance spectrum as the ordinate y; 7) Analysis of test results: The peak area values ​​of each herbicide component in the sample spectrum obtained in step 5) are respectively substituted into the corresponding standard curve obtained in step 6), and the content of the herbicide component in the sample is obtained by calculation.

2. A method for simultaneously detecting six trace herbicides in water as claimed in claim 1, characterized in that In step 1), the amount of ionic liquid used is 40-250 mg, the amount of 1,3,5-tris(4-aminophenyl)benzene used is 100-120 mg, and the amount of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde used is 80-100 mg.

3. A method for simultaneously detecting six trace herbicides in water as claimed in claim 1, characterized in that In step 2), the pH of the water sample is 4-8.

4. A method for simultaneously detecting six trace herbicides in water as claimed in claim 1, characterized in that In step 3), the amount of IL@COF material used is 2-20 mg.

5. A method for simultaneously detecting six trace herbicides in water as claimed in claim 1, characterized in that In step 5), the amount of water sample is 0.5-1 mL, the certain temperature is 20-40°C, and the standing time is 10-30 min.

6. A method for simultaneously detecting six trace herbicides in water as claimed in claim 1, characterized in that The conditions for the HPLC analysis in step 5) and step 6) are as follows: Shimadzu liquid chromatograph, including LC-20AD separation chromatography system, SIL-20A automatic injection system, CTO-20A column oven, SPD-20A UV / visible detector, and WatersXSelect chromatographic column. TM HSS T3, with acetonitrile as mobile phase A and 0.1% phosphoric acid as mobile phase B, gradient elution was performed: 0-15min 35%A; 15-25 min 35→45%A; 25-30min 45→90%A; 30-40min 90%A; detection wavelength was 210nm; column temperature was 35℃, and injection volume was 20μL.

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