CN111024850B - Preparation and application of paraquat molecular imprinting solid-phase microextraction coating solution - Google Patents
Preparation and application of paraquat molecular imprinting solid-phase microextraction coating solution Download PDFInfo
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Abstract
The invention discloses a preparation method and application of paraquat molecular imprinting solid-phase microextraction coating solution, wherein single-hydroxyl seven-element cucurbituril and paraquat are ground to prepare an inclusion compound, and the inclusion compound is bonded on a sol-gel network formed by polymerizing dichloromethane, gamma-glycidyl ether oxypropyl trimethoxysilane, hydroxyl-terminated polydimethylsiloxane, methyltrimethoxysilane, polymethylhydrosiloxane and 98% trifluoroacetic acid to obtain the coating solution. And preparing the coating solution into a stirring rod, and analyzing and determining paraquat pesticide residues in the environmental water sample or the fruit and vegetable sample by using high performance liquid chromatography. The coating is prepared by using the prepared coating solution, so that the special detection of paraquat can be realized, the detection limit is low, the sensitivity is good, the use is simple and convenient, and the detection requirements of trace paraquat in an environmental water sample and a food matrix can be met; in addition, the method has the characteristics of simple preparation, stable acid and alkali resistance of the coating, good thermal stability, less samples required for detection and less consumption of organic solvent.
Description
Technical Field
The invention relates to preparation and application of a molecularly imprinted solid-phase microextraction coating solution, in particular to preparation and application of a paraquat molecularly imprinted solid-phase microextraction coating solution.
Background
The Solid Phase Microextraction (SPME) is a novel sample pretreatment technology, and has the advantages of simplicity, rapidness, convenience, high efficiency, no need of solvents and the like. However, in the pretreatment of some samples, commercial solid phase microextraction coatings have the disadvantages of low selectivity, high price, short service life and the like, thereby limiting the application of the solid phase microextraction coatings.
The Molecularly Imprinted Polymer (MIP) is a polymer with a three-dimensional network structure, has the advantages of a biological recognition system and a chemical recognition system, has the characteristics of high selectivity, good stability, easiness in preparation and the like, can selectively recognize a target object in a complex sample, and is widely applied to sample pretreatment. The method can be used in combination with solid phase microextraction technology to make up for the disadvantage of low selectivity of solid phase microextraction technology. Therefore, the molecularly imprinted polymer which is completely matched with the target molecule on the spatial structure and the binding site is prepared, and then the polymer is used as a coating for solid phase microextraction, so that the molecularly imprinted solid phase microextraction technology is formed. The technology makes up the defects between the two, and has great development prospect.
Paraquat, the chemical name of which is 1-1-dimethyl-4-4-bipyridine cation salt, is a quick biocidal herbicide and has a contact action and a certain systemic action. Can be rapidly absorbed by green tissues of plants to make the plants wither. Has no effect on non-green tissues. It is rapidly combined with soil in soil to passivate, and is ineffective for plant roots and perennial underground stems and perennial roots. The characteristic of easy water solubility of paraquat is easy to pollute the environment, and has strong lethal effect on human beings and animals. The ionic characteristic of paraquat also makes it insoluble in organic solvents, so that it is difficult to perform enrichment concentration by using a common sample pretreatment method, the detection limit of the sample is high, and the detection requirements for trace paraquat in environment and food are difficult to meet.
Disclosure of Invention
The invention aims to provide preparation and application of paraquat molecular imprinting solid-phase microextraction coating solution. The coating is prepared by using the prepared paraquat molecular imprinting solid-phase microextraction coating solution, so that the special detection of paraquat can be realized, the detection limit is low, the sensitivity is good, the use is simple and convenient, and the detection requirements of trace paraquat in an environmental water sample and a food matrix can be met; in addition, the method has the characteristics of simple preparation, stable acid and alkali resistance of the coating, good thermal stability, less samples required for detection and less consumption of organic solvent.
The technical scheme of the invention is as follows: a solid inclusion compound of monohydroxy heptatomic cucurbituril-paraquat is prepared by taking monohydroxy heptatomic cucurbituril as a functional carrier and paraquat as a template molecule through a grinding method, and the inclusion compound is bonded on a sol-gel network formed by polymerizing dichloromethane, gamma-glycidyl ether oxypropyl trimethoxysilane, hydroxyl-terminated polydimethylsiloxane, methyltrimethoxysilane, polymethylhydrosiloxane and 98% trifluoroacetic acid to prepare the solid-phase microextraction coating solution of paraquat molecular imprinting.
The preparation method of the paraquat molecular imprinting solid-phase microextraction coating solution comprises the following specific steps:
(1) putting the monohydroxy seven-membered cucurbituril and the paraquat into a mortar, adding water to be mixed into a thick state, grinding the mixture until a monohydroxy seven-membered cucurbituril-paraquat inclusion compound is formed, and drying the monohydroxy seven-membered cucurbituril-paraquat inclusion compound to obtain monohydroxy seven-membered cucurbituril-paraquat inclusion compound powder;
(2) adding monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder into a polyvinyl chloride centrifugal tube, then adding 98% trifluoroacetic acid, oscillating for 1-3min, then sequentially adding dichloromethane, gamma-glycidyl ether oxypropyl trimethoxysilane, hydroxyl-terminated polydimethylsiloxane, methyltrimethoxysilane and polymethylhydrosiloxane, mixing for 2-4min on a vortex oscillator, centrifuging, and then taking supernatant, namely the paraquat molecular imprinting solid-phase microextraction coating solution.
In the preparation of the paraquat molecular imprinting solid-phase microextraction coating solution, in the step 1), the stoichiometric ratio of the mixture of the monohydroxy cucurbituril and paraquat is 1: 1.
in the preparation of the paraquat molecular imprinting solid-phase microextraction coating solution, the grinding time in the step 1) is more than 30 min.
In the preparation of the paraquat molecular imprinting solid-phase microextraction coating solution, the drying temperature in the step 1) is 45-55 ℃, and the time is 10-15 h.
In the step 2), for each 20mg of monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder, 300 μ L of trifluoroacetic acid, 700 μ L of dichloromethane, 300 μ L of gamma-glycidoxypropyltrimethoxysilane, 300 μ L of hydroxyl-terminated polydimethylsiloxane, 50 μ L of methyltrimethoxysilane and 50 μ L of polymethylhydrosiloxane are added.
In the preparation of the paraquat molecular imprinting solid-phase microextraction coating solution, the rotation speed of the centrifugation in the step 2) is 11000-13000r/min, and the centrifugation time is 3-7 min.
The application of the paraquat molecular imprinting solid-phase microextraction coating solution is characterized in that the coating solution is prepared into a paraquat molecular imprinting solid-phase microextraction stirring rod, an environmental water sample or a fruit and vegetable sample is pretreated, and the paraquat molecular imprinting solid-phase microextraction stirring rod and a high performance liquid chromatography are used for analyzing and determining paraquat pesticide residue in the environmental water sample or the fruit and vegetable sample.
In the application of the paraquat molecular imprinting solid-phase microextraction coating solution, the preparation process of the paraquat molecular imprinting solid-phase microextraction stirring rod is as follows:
(1) pretreatment of the glass tube: selecting a glass tube with the outer diameter of 1.0-1.1mm, the inner diameter of 0.9-1.0mm and the length of 1.5cm as a carrier, then placing the cut iron core into the glass tube, sintering and sealing two ends of the glass tube by using an alcohol burner, soaking the glass tube in 1.0mol/L NaOH solution for 10-15 hours to promote the surface to have richer silicon hydroxyl groups, then washing the glass tube with deionized water, then placing the glass tube in 0.1mol/L hydrochloric acid solution for 0.5-1 hour to neutralize excessive alkali on the surface, also washing the glass tube with the deionized water, and placing the glass tube into a vacuum drying oven to be dried for later use;
(2) immersing the treated glass tube into paraquat molecular imprinting solid-phase micro-extraction coating solution for repeated coating, controlling the thickness of the coating to be 450-500 mu m, and placing the coated glass tube under the protection of nitrogen for 10-15h for gelling;
(3) aging of the coating: carrying out programmed heating ageing on the glass tube coated with the coating under the protection of nitrogen, firstly keeping the temperature at 55-65 ℃ for 50-70min, then heating to 110-130 ℃ for 50-70min, finally keeping the temperature at 170-190 ℃ for 20-40min, and collecting the coating for later use after the glass tube is naturally cooled;
(4) cleaning a coating: the aged coating needs to be cleaned before use to remove imprinting molecules and unreacted substances on the coating, and the coating is firstly soaked in secondary water at the temperature of 70-90 ℃ for 0.5-1.5h at constant temperature, then is placed into methanol for soaking for 20-40min, is then stirred and cleaned for multiple times by 1% hydrochloric acid methanol solution, is parallelly connected with a high performance liquid chromatography to detect whether template molecules are completely eluted, and after the template molecules are completely eluted, the coating is refluxed and cleaned in dichloromethane at the temperature of 30-50 ℃ for 1-3h, and is dried by nitrogen.
In the application of the paraquat molecular imprinting solid-phase microextraction coating solution, after the coating in the step (3) is aged, the nitrogen is protected until the cooling is finished in the natural cooling process of the glass tube.
The invention has the advantages of
1. The invention introduces the molecular imprinting technology into the solid phase micro-extraction coating, thereby realizing the detection of paraquat;
2. the coating can achieve specificity detection on the paraquat, and other coexisting quaternary ammonium salt compounds do not interfere with the determination of the paraquat; the method has low detection limit and good sensitivity, reaches the level of ng/L and is far lower than the maximum residual MRL of paraquat in environmental water samples and foods formulated by European Union; the method is simple and convenient to use, and can meet the detection requirements of trace paraquat in an environmental water sample and a food matrix;
3. the preparation method is simple, the coating is stable in property, and is resistant to acid, alkali and organic solvents, and the thermal stability is good;
4. when the method is used for detection, the required sample amount is small, only 5 ml of water sample is needed, only 2 g of solid sample is needed, the consumed organic solvent amount is small, and the organic solvent amount consumed in one complete extraction and analysis process is not more than 2 ml.
Drawings
FIG. 1 is a flow chart of a method for preparing a coating layer of paraquat molecularly imprinted polymer of example 1;
FIG. 2 is an IR spectrum of a coating layer of paraquat molecularly imprinted polymer of example 2;
FIG. 3 is a comparison of the adsorption capacity of the molecularly imprinted polymer coating of paraquat and the non-imprinted molecular coating of example 3 for paraquat;
fig. 4 is a liquid chromatogram of solid phase microextraction small stick combined high performance liquid chromatography for detecting paraquat in vegetables prepared by paraquat molecularly imprinted polymer coating in example 4.
Detailed Description
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.
Examples of the invention
Example 1: preparation of paraquat molecularly imprinted polymer sol-gel solution:
(1) weighing Paraquat 178mg and monohydroxy cucurbituril 821mg (n)Paraquat (Paraquat)：nMonohydroxy seven-element cucurbituril1:1) putting the mixture into an agate grinding bowl, adding 50 mu L of secondary water, fully grinding for 30min to obtain the monohydroxy heptatomic cucurbituril-paraquat solid inclusion compound, drying the inclusion compound at 50 ℃ for 12h, and grinding the inclusion compound into powder by using an agate grinding bowl to obtain the monohydroxy heptatomic cucurbituril-paraquat solid inclusion compound;
(2) taking 20mg of the ground inclusion compound into a 4mL polyvinyl chloride centrifuge tube, adding 300 mu L of 98% trifluoroacetic acid, and shaking for 2 min;
(3) sequentially adding 700 μ L of dichloromethane, 300 μ L of gamma-glycidoxypropyltrimethoxysilane, 300 μ L of hydroxyl-terminated polydimethylsiloxane, 50 μ L of methyltrimethoxysilane and 50 μ L of polymethylhydrosiloxane, and vortexing for 3 min;
(4) centrifuging at 12000r/min for 5min, and taking the supernatant as the solution of paraquat molecularly imprinted polymer sol-gel coating.
Example 2: preparation of molecularly imprinted solid-phase microextraction stirring rod (MIP-SBSE)
(1) Selecting a glass tube with the outer diameter of 1.0-1.1mm, the inner diameter of 0.9-1.0mm and the length of 1.5cm as a carrier, then placing the cut iron core into the glass tube, sintering and sealing two ends of the glass tube by using an alcohol burner, soaking the glass tube in 1.0mol/L NaOH solution for 12 hours to promote the surface to have richer silicon hydroxyl groups, then washing the glass tube with deionized water, then placing the glass tube in 0.1mol/L hydrochloric acid solution for 0.5 hours to neutralize the excessive alkali on the surface, similarly washing the glass tube with the deionized water, and placing the glass tube into a vacuum drying oven to be dried for later use;
(2) immersing the treated glass rod into the molecular imprinting sol-gel coating solution for repeated coating, wherein the thickness can be controlled by coating times, generally 15 times, the thickness of the coating is controlled to be about 480 mu m, and placing the coated small rod under the protection of nitrogen for 12 hours for gelling;
(3) carrying out programmed heating aging on the coating under the protection of nitrogen, firstly keeping the temperature at 60 ℃ for 60min, then slowly heating to 120 ℃ for 60min, finally keeping the temperature at 180 ℃ for 30min, and collecting the coating for later use after the small rod is naturally cooled (the nitrogen is protected until the cooling is finished);
(4) the aged molecular imprinting solid-phase microextraction small rod needs to be subjected to coating cleaning before use so as to remove unreacted substances on the coating, and is firstly soaked in secondary water at the temperature of 80 ℃ for 1 hour at constant temperature, then is placed into methanol for soaking for 30 minutes, then is stirred and cleaned for multiple times by using 1% hydrochloric acid methanol solution, whether template molecules paraquat is completely eluted is detected by using high performance liquid chromatography, after the template molecules are completely eluted, the small rod is subjected to reflux cleaning in dichloromethane at the temperature of 40 ℃ for 2 hours, and finally is dried by using nitrogen for later use.
Example 3: comparison of adsorption Performance of Paraquat molecular imprinting solid-phase microextraction stirring rod (MIP-SBSE) and solid-phase microextraction stirring rod (NIP-SBSE) without molecular imprinting
Preparing 1,2,4,6,8,10,20,40,60,80,100,120ng/mL paraquat standard solution series, respectively carrying out adsorption extraction by using paraquat MIP-SBSE and NIP-SBSE under optimized experimental conditions, and carrying out liquid chromatography analysis and determination. The result shows that the extraction capacity of the molecular imprinting small stick is larger than that of the non-imprinting small stick under the same paraquat concentration, the quantity of the paraquat extracted by the molecular imprinting small stick is 3.6 times that of the non-imprinting small stick, the preparation of the molecular imprinting small stick is successful, an imprinting cavity is formed in the molecular imprinting small stick, the template molecule can be memorized, the template molecule can be specifically adsorbed, but the non-imprinting small stick can not form the imprinting cavity, and therefore the non-specific adsorption to the paraquat is realized.
Example 4: analysis and detection of paraquat in environmental water sample and vegetables by using monohydroxy seven-element melon-paraquat molecular imprinting solid-phase microextraction stirring rod in combination with high performance liquid chromatography
Under the optimized extraction experimental conditions, the extraction time is 50min, the extraction temperature is room temperature, the stirring speed is 400r/min, the analysis time is 10min, the analysis temperature is 30 ℃, small bars of the molecular imprinting solid phase micro-extraction are used for extracting paraquat of environmental water samples and vegetable sample varieties, the content of the paraquat is measured by high performance liquid chromatography, and the linear range, the detection limit and the quantitative limit of the method are shown in table 1. As can be seen from Table 1, the detection limit of the method is far lower than the maximum residual quantity (MRL) of paraquat in environmental water samples and vegetable samples specified by European Union, and the method has high detection sensitivity. The paraquat standard solutions with different concentrations are added into the environmental water sample and the vegetable sample, the relative recovery rate of the method is calculated, the result is shown in table 2, the recovery rate of the method is 82.04% -104.98%, the requirement that the pesticide residue determination recovery rate is 70% -120% can be met, in addition, the RSD value is below 9%, the established method is good in accuracy and repeatability, and the method is suitable for analyzing and detecting trace paraquat.
Table 1 detection limits, linear ranges, correlation coefficients, etc. of paraquat in environmental water samples and vegetables
TABLE 2 addition of environmental water sample and vegetable sample for recovery experiment
Example 5: the preparation method of the paraquat molecular imprinting solid-phase microextraction coating solution comprises the following specific steps:
(1) and (2) mixing the mono-hydroxyl seven-element cucurbituril and the paraquat in a stoichiometric ratio of 1:1, putting the mixture into a mortar, adding water to be mixed into a thick paste, grinding the paste for 30min to form a monohydroxy heptatomic cucurbituril-paraquat inclusion compound, and drying the monohydroxy heptatomic cucurbituril-paraquat inclusion compound for 10h at the temperature of 45 ℃ to obtain monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder;
(2) adding 20mg of monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder into a polyvinyl chloride centrifugal tube, then adding 300 mu L of 98% trifluoroacetic acid, oscillating for 1min, then sequentially adding 700 mu L of dichloromethane, 300 mu L of gamma-glycidyl ether oxypropyl trimethoxysilane, 300 mu L of hydroxyl-terminated polydimethylsiloxane, 50 mu L of methyl trimethoxysilane and 50 mu L of polymethylhydrosiloxane, mixing for 2min on a vortex oscillator, centrifuging, and then taking supernatant, namely paraquat molecular imprinting solid-phase micro-extraction coating solution.
Example 6: the preparation method of the paraquat molecular imprinting solid-phase microextraction coating solution comprises the following specific steps:
(1) and (2) mixing the single-hydroxyl seven-element cucurbituril and the paraquat in a stoichiometric ratio of 1:1, putting the mixture into a mortar, adding water to be mixed into a thick paste, grinding for 50min to form a monohydroxy heptatomic cucurbituril-paraquat inclusion compound, and drying the monohydroxy heptatomic cucurbituril-paraquat inclusion compound for 15h at the temperature of 55 ℃ to obtain monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder;
(2) adding 20mg of monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder into a polyvinyl chloride centrifugal tube, then adding 300 mu L of 98% trifluoroacetic acid, oscillating for 3min, then sequentially adding 700 mu L of dichloromethane, 300 mu L of gamma-glycidyl ether oxypropyl trimethoxysilane, 300 mu L of hydroxyl-terminated polydimethylsiloxane, 50 mu L of methyl trimethoxysilane and 50 mu L of polymethylhydrosiloxane, mixing for 4min on a vortex oscillator, centrifuging, and then taking supernatant, namely paraquat molecular imprinting solid-phase micro-extraction coating solution.
Example 7: the preparation process of the paraquat molecular imprinting solid-phase microextraction stirring rod comprises the following steps:
(1) pretreatment of the glass tube: selecting a glass tube with the outer diameter of 1.0mm, the inner diameter of 0.9mm and the length of 1.5cm as a carrier, then placing the cut iron core into the glass tube, sintering and sealing two ends of the glass tube by using an alcohol blast burner, soaking the glass tube in 1.0mol/L NaOH solution for 10 hours to promote the surface to have richer silicon hydroxyl groups, then cleaning the glass tube by using deionized water, then placing the glass tube in 0.1mol/L hydrochloric acid solution for 0.5 hour to neutralize the excessive alkali on the surface, similarly cleaning the glass tube by using the deionized water, and placing the glass tube into a vacuum drying oven to be dried for later use;
(2) immersing the treated glass tube into paraquat molecular imprinting solid-phase microextraction coating solution for repeated coating, controlling the thickness of the coating to be 450 mu m, and placing the coated glass tube under the protection of nitrogen for 10h to form gel;
(3) aging of the coating: carrying out programmed heating and aging on the glass tube coated with the coating under the protection of nitrogen, keeping the temperature at 55 ℃ for 50min, then heating to 110 ℃ for 50min, and finally keeping the temperature at 170 ℃ for 20min, and collecting the coating for later use after the glass tube is naturally cooled and is protected by nitrogen in the whole cooling process;
(4) cleaning a coating: the aged coating needs to be cleaned before use to remove the imprinted molecules and unreacted substances on the coating, and the coating is firstly soaked in secondary water at 70 ℃ for 0.5h at constant temperature, then is placed in methanol for soaking for 20min, is repeatedly stirred and cleaned by 1% hydrochloric acid methanol solution, is parallelly connected with a high performance liquid chromatography to detect whether the template molecules are completely eluted, and is cleaned in dichloromethane at 30 ℃ for 1h in a backflow manner after the template molecules are completely eluted, and is dried by nitrogen.
Example 8: the preparation process of the paraquat molecular imprinting solid-phase microextraction stirring rod comprises the following steps:
(1) pretreatment of the glass tube: selecting a glass tube with the outer diameter of 1.1mm, the inner diameter of 1.0mm and the length of 1.5cm as a carrier, then placing the cut iron core into the glass tube, sintering and sealing two ends of the glass tube by using an alcohol blast burner, soaking the glass tube in 1.0mol/L NaOH solution for 15 hours to promote the surface to have richer silicon hydroxyl groups, then cleaning the glass tube by using deionized water, placing the glass tube in 0.1mol/L hydrochloric acid solution for 1 hour to neutralize excessive alkali on the surface, similarly, completely washing the glass tube by using the deionized water, and placing the glass tube into a vacuum drying oven to be dried for later use;
(2) immersing the treated glass tube into paraquat molecular imprinting solid-phase microextraction coating solution for repeated coating, controlling the thickness of the coating to be 500 mu m, and placing the coated glass tube under the protection of nitrogen for 15h to form gel;
(3) aging of the coating: carrying out programmed heating and aging on the glass tube coated with the coating under the protection of nitrogen, firstly keeping the temperature at 65 ℃ for 70min, then heating to 130 ℃ for 70min, finally keeping the temperature at 190 ℃ for 40min, and collecting for later use after the glass tube is naturally cooled and is protected by nitrogen in the whole cooling process;
(4) cleaning a coating: the aged coating needs to be cleaned before use to remove imprinted molecules and unreacted substances on the coating, and is firstly soaked in secondary water at the temperature of 90 ℃ for 1.5 hours at constant temperature, then is placed in methanol for soaking for 40 minutes, then is stirred and cleaned for multiple times by using 1% hydrochloric acid methanol solution, is parallelly connected with a high performance liquid chromatography to detect whether template molecules are completely eluted, and after the template molecules are completely eluted, the coating is cleaned in dichloromethane at the temperature of 50 ℃ for 3 hours in a backflow mode, and is dried by using nitrogen.
The above description is only for the purpose of illustrating the present invention and the appended claims, and the scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution and the inventive concept of the present invention within the technical scope of the present invention.
Claims (10)
1. A preparation method of paraquat molecular imprinting solid-phase microextraction coating solution is characterized by comprising the following steps: the method comprises the steps of taking monohydroxy heptatomic cucurbituril as a functional carrier, taking paraquat as a template molecule, preparing a solid inclusion compound of monohydroxy heptatomic cucurbituril-paraquat by a grinding method, and bonding the inclusion compound on a sol-gel network formed by polymerizing dichloromethane, gamma-glycidyl ether oxypropyl trimethoxysilane, hydroxyl-terminated polydimethylsiloxane, methyltrimethoxysilane, polymethylhydrosiloxane and 98% trifluoroacetic acid to prepare the paraquat molecular imprinting solid-phase microextraction coating solution.
2. The preparation method of paraquat molecular imprinting solid-phase microextraction coating solution according to claim 1, characterized in that the specific preparation method of said coating solution is as follows:
(1) putting the monohydroxy seven-membered cucurbituril and the paraquat into a mortar, adding water to be mixed into a thick state, grinding the mixture until a monohydroxy seven-membered cucurbituril-paraquat inclusion compound is formed, and drying the monohydroxy seven-membered cucurbituril-paraquat inclusion compound to obtain monohydroxy seven-membered cucurbituril-paraquat inclusion compound powder;
(2) adding monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder into a polyvinyl chloride centrifugal tube, then adding 98% trifluoroacetic acid, oscillating for 1-3min, then sequentially adding dichloromethane, gamma-glycidyl ether oxypropyl trimethoxysilane, hydroxyl-terminated polydimethylsiloxane, methyltrimethoxysilane and polymethylhydrosiloxane, mixing for 2-4min on a vortex oscillator, centrifuging, and then taking supernatant, namely the paraquat molecular imprinting solid-phase microextraction coating solution.
3. The method for preparing paraquat molecular imprinting solid-phase microextraction coating solution according to claim 2, characterized in that: the stoichiometric ratio of the mixture of the monohydroxy seven-element cucurbituril and the paraquat in the step (1) is 1: 1.
4. the method for preparing paraquat molecular imprinting solid-phase microextraction coating solution according to claim 2, characterized in that: the grinding time in the step (1) is more than 30 min.
5. The method for preparing paraquat molecular imprinting solid-phase microextraction coating solution according to claim 2, characterized in that: the drying temperature in the step (1) is 45-55 ℃, and the drying time is 10-15 h.
6. The method for preparing paraquat molecular imprinting solid-phase microextraction coating solution according to claim 2, characterized in that: in the step (2), for every 20mg of monohydroxy heptatomic cucurbituril-paraquat inclusion compound powder, 300 mu L of trifluoroacetic acid, 700 mu L of dichloromethane, 300 mu L of gamma-glycidyl ether oxypropyl trimethoxysilane, 300 mu L of hydroxyl-terminated polydimethylsiloxane, 50 mu L of methyl trimethoxysilane and 50 mu L of polymethylhydrosiloxane are added.
7. The method for preparing paraquat molecular imprinting solid-phase microextraction coating solution according to claim 2, characterized in that: the rotation speed of the centrifugation in the step (2) is 11000-13000r/min, and the centrifugation time is 3-7 min.
8. Use of the paraquat molecular imprinting solid-phase microextraction coating solution obtained by the preparation method according to any one of claims 1 to 7, characterized in that: the coating solution is prepared into a paraquat molecular imprinting solid-phase microextraction stirring rod, an environmental water sample or a fruit and vegetable sample is pretreated, and paraquat pesticide residue in the environmental water sample or the fruit and vegetable sample is analyzed and determined by combining with high performance liquid chromatography.
9. The application of the paraquat molecular imprinting solid-phase microextraction coating solution according to claim 8, wherein the preparation process of the paraquat molecular imprinting solid-phase microextraction stirring rod is as follows:
(1) pretreatment of the glass tube: selecting a glass tube with the outer diameter of 1.0-1.1mm, the inner diameter of 0.9-1.0mm and the length of 1.5cm as a carrier, then placing the cut iron core into the glass tube, sintering and sealing two ends of the glass tube by using an alcohol burner, soaking the glass tube in 1.0mol/L NaOH solution for 10-15 hours to promote the surface to have richer silicon hydroxyl groups, then washing the glass tube with deionized water, then placing the glass tube in 0.1mol/L hydrochloric acid solution for 0.5-1 hour to neutralize excessive alkali on the surface, also washing the glass tube with the deionized water, and placing the glass tube into a vacuum drying oven to be dried for later use;
(2) immersing the treated glass tube into paraquat molecular imprinting solid-phase micro-extraction coating solution for repeated coating, controlling the thickness of the coating to be 450-500 mu m, and placing the coated glass tube under the protection of nitrogen for 10-15h to form gel;
(3) aging the coating: carrying out programmed heating ageing on the glass tube coated with the coating under the protection of nitrogen, firstly keeping the temperature at 55-65 ℃ for 50-70min, then heating to 110-130 ℃ for 50-70min, finally keeping the temperature at 170-190 ℃ for 20-40min, and collecting the coating for later use after the glass tube is naturally cooled;
(4) cleaning a coating: the aged coating needs to be cleaned before use to remove imprinting molecules and unreacted substances on the coating, and the coating is firstly soaked in secondary water at the temperature of 70-90 ℃ for 0.5-1.5h at constant temperature, then is placed into methanol for soaking for 20-40min, is then stirred and cleaned for multiple times by 1% hydrochloric acid methanol solution, is parallelly connected with a high performance liquid chromatography to detect whether template molecules are completely eluted, and after the template molecules are completely eluted, the coating is refluxed and cleaned in dichloromethane at the temperature of 30-50 ℃ for 1-3h, and is dried by nitrogen.
10. The use of paraquat molecularly imprinted solid phase microextraction coating solution according to claim 9, characterized in that: and (4) after the coating in the step (3) is aged, in the natural cooling process of the glass tube, the nitrogen is protected until the cooling is finished.
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