A solid phase microextraction coating and its preparation method and application

Abstract

This application provides a solid-phase microextraction coating based on polymerized 11,12-dihydroindolo[2,3-a]carbazole ionic liquid, its preparation method, and its application. The method uses 11,12-dihydroindolo[2,3-a]carbazole as the functional monomer, tetrabutylammonium perchlorate as the electrolyte, and hexafluorophosphate ionic liquid as the dopant. A solid-phase microextraction coating is prepared on a stainless steel wire surface by electrochemical polymerization using cyclic voltammetry. The resulting coating exhibits good film-forming properties, strong thermal stability, high sensitivity, and excellent extraction response for phenolic compounds. The method is simple to operate, operates under mild conditions, is low-cost, and environmentally friendly. The coating preparation process requires only one cyclic voltammetric scan using a three-electrode system, making it suitable for widespread application.

Description

Technical Field

[0001] This application belongs to the field of chemical analysis technology, and in particular relates to a solid-phase microextraction coating based on polymerized 11,12-dihydroindolo[2,3-a]carbazole-ionic liquid, its preparation method and its application. Background Technology

[0002] With the development of industry and agriculture, the discharge of phenolic substances into environmental water bodies and soil is constantly increasing. Numerous studies have shown that the concentration of phenolic substances in surface water reaches micrograms or higher, and the pollution situation is even more severe in relatively underdeveloped developing countries. Phenolic compounds have persistent and bioaccumulative effects and are typical carcinogenic, teratogenic, and mutagenic environmental pollutants. Therefore, monitoring phenolic compounds in the environment has significant practical implications.

[0003] Currently, sample pretreatment is a crucial step in the construction of analytical methods for detecting phenolic compounds, typically requiring large amounts of reagents and cumbersome procedures. Solid-phase microextraction (SPME), a new technology developed from solid-phase extraction, integrates sampling, extraction, concentration, and injection. It can be coupled online with analytical instruments such as GC-MS and is widely used in environmental analysis, pesticide residues, and food analysis. Headspace solid-phase microextraction (HS-SPME) offers advantages such as low cost, ease of operation, and rapid pre-concentration. It is a solvent-free sample preparation method that effectively eliminates sample matrix interference.

[0004] However, the existing technology still has the following shortcomings: (1) The film-forming properties of single monomer coatings are not ideal, the thermal stability is poor, and the extraction capacity and selectivity of target analytes are limited; (2) Copolymerization of two different monomers requires precise control of the ratio and polymerization conditions, which is difficult to prepare; (3) Ionic liquids are mostly introduced by physical coating, which has poor stability; (4) The sensitivity and selectivity for simultaneous detection of multiple phenolic compounds in environmental samples are insufficient. Summary of the Invention

[0005] The purpose of this invention is to solve at least one problem of the prior art by providing a method for preparing a solid-phase microextraction coating based on polymerized 11,12-dihydroindolo[2,3-a]carbazole ionic liquid. This method is simple to operate, has mild conditions, and produces a coating with a dual microstructure and excellent performance.

[0006] Another object of the present invention is to provide a solid-phase microextraction coating prepared by the preparation method, and the application of the coating in the detection of phenolic compounds in environmental samples.

[0007] According to one aspect of this application, a method for preparing a solid-phase microextraction coating is provided, characterized by comprising the following steps: S1: Constructing a three-electrode system: pre-treated stainless steel wire is used as the working electrode; Ag / AgCl is used as the reference electrode, and platinum wire is used as the auxiliary electrode; S2: An electrolyte is prepared by dissolving the functional monomer, electrolyte and dopant in acetonitrile solvent using 11,12-dihydroindolo[2,3-a]carbazole as the functional monomer, tetrabutylammonium perchlorate as the electrolyte, hexafluorophosphate ionic liquid as the dopant. S3: Apply current to the three-electrode system and electrochemically polymerize the stainless steel wire surface using cyclic voltammetry to prepare the solid-phase microextraction coating. S4: Perform programmed temperature aging on the coating; S5: Assemble the coating onto the solid phase microextraction injector.

[0008] In some embodiments, the ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonylimide (BOP), 1-hexadecyl-3-methylimidazolium hexafluorophosphate (C16MIMPF6), 1-octyl-3-methylimidazolium hexafluorophosphate (OMIMPF6), and 1-propyl-3-methylimidazolium hexafluorophosphate ([PMIm]PF6).

[0009] In some embodiments, the ionic liquid is 1-hexadecyl-3-methylimidazolium hexafluorophosphate.

[0010] In some implementations, the cyclic voltammetry parameters are: initial potential 0.0 V, high potential 2.0 V, scan rate 0.05 V / s, number of scan segments 50, and sensitivity 1 × 10⁻⁶. - ³A / V.

[0011] In some embodiments, the electrolyte contains 0.008 mol / L of 11,12-dihydroindolo[2,3-a]carbazole monomer, 5 μg / mL of ionic liquid, and 0.1 mol / L of tetrabutylammonium perchlorate.

[0012] In some implementations, the programmed temperature aging process is as follows: from 20 °C to 110 °C in 25 min, held at 110 °C for 65 min, and then increased to 260 °C in 90 min.

[0013] According to another aspect of this application, a solid-phase microextraction coating prepared by the aforementioned method is provided, the coating containing ionic liquid-doped polymeric 11,12-dihydroindolo[2,3-a]carbazole. According to another aspect of this application, a method for detecting phenolic compounds using the aforementioned solid-phase microextraction coating is characterized by comprising the following steps: (1) Insert the solid phase microextraction injector into the extraction bottle containing the phenolic compound sample for headspace solid phase microextraction. The extraction conditions are: extraction time 10-40 min, stirring rate 300-700 r / min, extraction temperature 20-60 ℃, and elution time 1-5 min. (2) After extraction, the sample injector is inserted into the gas chromatograph-mass spectrometer for analysis and detection.

[0014] In some implementations, the headspace solid-phase microextraction conditions are: extraction time 30 min, stirring rate 500 r / min, extraction temperature 40 ℃, and resolution time 3 min.

[0015] In some embodiments, the phenolic compound is one or more of 2,4,6-trichlorophenol, 3-chloro-4-fluorophenol, 3-aminophenol, 2,6-di-tert-butyl-4-aminophenol, 4-aminophenol, and 4-chloro-3,5-dimethylphenol.

[0016] Compared with the prior art, the advantages of this application are: (1) The present invention uses 11,12-dihydroindolo[2,3-a]carbazole as a functional monomer. This monomer has both indole and carbazole structural features and two electrochemical polymerization sites (oxidation peaks appear near 1.4 V and 1.6 V, respectively). Electrochemical polymerization on the surface of stainless steel wire can form a dual microstructure coating (composed of large particles and small particles), which overcomes the problems of poor film-forming properties and insufficient thermal stability of single monomer coatings. The dual structure can be achieved without copolymerization of two different monomers.

[0017] (2) This invention incorporates hexafluorophosphate ionic liquids into the coating during electrochemical polymerization by adding them to the electrolyte. Compared with physical coating methods, this doping is more robust and stable, effectively improving the microstructure of the SPME coating and making the coating surface rougher, more porous, and denser. The coating doped with C16MIMPF6 has the most abundant and uniformly distributed small particle adhesion structure, significantly improving the coating's extraction response to phenolic compounds.

[0018] (3) The solid-phase microextraction coating prepared in this invention, when coupled with GC-MS, showed good linear response to six phenolic compounds in the concentration range of 0.5-2.5 μg / mL under optimized conditions, indicating that the method has good practicality.

[0019] (4) The method of the present invention is simple to operate, mild, low in cost and environmentally friendly. The coating preparation process only requires one cyclic voltammetric scan of the three-electrode system, which is suitable for promotion and application. Attached Figure Description

[0020] The technical solution of this application will be further described below with reference to the accompanying drawings and embodiments.

[0021] Figure 1 These are cyclic voltammetry curves of polymerized 11,12-dihydroindolo[2,3-a]carbazole, polymerized indole, polymerized carbazole, and liquids doped with different ionic liquids; (A: 11,12-dihydroindolo[2,3-a]carbazole; B: carbazole; C: indole; D: A+BMIMPF6; E: A+BOP; F: A+C16MIMPF6; G: A+OMIMPF6; H: A+PMIMPF6) Figure 2 This is a SEM image of a pure polymerized 11,12-dihydroindolo[2,3-a]carbazole coating. Figure 3 This is a SEM image of a polymerized indole coating; Figure 4 It is a SEM image of the polymeric carbazole coating; Figure 5 This is a SEM image of the polymer coating of BMIMPF6 doped with 11,12-dihydroindolo[2,3-a]carbazole. Figure 6 This is a SEM image of BOP doped with polymerized 11,12-dihydroindolo[2,3-a]carbazole; Figure 7 This is a SEM image of the polymer coating of 11,12-dihydroindolo[2,3-a]carbazole-doped C16MIMPF6 (preferred embodiment). Figure 8 This is a SEM image of OMIMPF6 doped with polymerized 11,12-dihydroindolo[2,3-a]carbazole. Figure 9 This is a SEM image of PMIMPF6 doped with polymerized 11,12-dihydroindolo[2,3-a]carbazole. Figure 10 The effect of different comonomers on peak area; Figure 11The effect of different ionic liquids on peak area; Figure 12 The effect of extraction time on the response peak area; Figure 13 The effect of stirring rate on the response peak area; Figure 14 This refers to the effect of extraction temperature on peak area; Figure 15 This relates to the effect of resolution time on the response peak area; Figure 16 It is the standard curve graph of the method. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0023] Table 1 Main Instruments

[0024] Table 2 Main Reagents

[0025] Base material treatment: A stainless steel wire 1.8 cm in length and 0.2 mm in diameter was used as the base material. First, the required length of stainless steel wire was precisely measured and cut using a ruler. Then, the stainless steel wire was repeatedly polished on a smooth table until its surface was smooth and straight. The polished stainless steel wire was placed in a glass beaker and immersed in a 1:1 mixture of nitric acid and deionized water to initially remove the oxide layer and oil stains from the surface of the stainless steel wire. The beaker was then placed in an ultrasonic cleaner and ultrasonically treated for 5 minutes at room temperature to further remove minute impurities from the surface of the stainless steel wire. After ultrasonic treatment, the wire was rinsed twice with deionized water to remove residual acid, and then twice with anhydrous ethanol to remove moisture and organic impurities. Finally, the stainless steel wire was allowed to air dry naturally or dried in an electric heating drying oven for later use.

[0026] Example 1: Preparation of a solid-phase microextraction coating of polymerized 11,12-dihydroindolo[2,3-a]carbazole doped with C16MIMPF6 S1: An electrolyte was prepared by dissolving 11,12-dihydroindolo[2,3-a]carbazole as the functional monomer, tetrabutylammonium perchlorate as the electrolyte, and C16MIMPF6 as the dopant in acetonitrile. The concentration of 11,12-dihydroindolo[2,3-a]carbazole was 0.008 mol / L, the concentration of tetrabutylammonium perchlorate was 0.1 mol / L, and the concentration of C16MIMPF6 was 5 μg / mL.

[0027] S2: Using pretreated stainless steel wire as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, a three-electrode system is formed, and the electrodes are immersed in the electrolyte.

[0028] S3: Apply current to the counter electrode and prepare the solid-phase microextraction coating using cyclic voltammetry; the cyclic voltammetry parameters are: initial potential 0 V, high potential 2.0 V, scan rate 0.05 V / s, number of scan cycles 50, sensitivity 1×10⁻⁶. -³ A / V. After polymerization, remove the stainless steel wire, rinse with distilled water and anhydrous ethanol, and air dry.

[0029] S4: Perform programmed temperature aging on the coating: increase the temperature from 20 degrees Celsius to 110 degrees Celsius in 25 minutes, hold at 110 degrees Celsius for 65 minutes, and then increase the temperature to 260 degrees Celsius in 90 minutes.

[0030] Table 3 Aging Procedure

[0031] S5: After mixing epoxy resin and acyl oxy resin in a 1:1 ratio, the extraction head is attached to the micro-injection needle and air-dried for 24 hours to obtain a solid-phase microextraction injector.

[0032] Examples 2-5: Methods for preparing polymer coatings doped with BMIMPF6, OMIMPF6, PMIMPF6, and BOP are provided respectively. These methods are the same as in Example 1, except that C16MIMPF6 in the electrolyte is replaced with the corresponding ionic liquid of equal concentration.

[0033] Comparative Examples 1-3: Methods for preparing pure polymeric 11,12-dihydroindolo[2,3-a]carbazole coating, pure polymeric carbazole coating, and pure polymeric indole coating are provided respectively. Compared with Example 1, no ionic liquid is added to the electrolyte, and the other conditions are the same.

[0034] Table 4 - Electrolyte composition and ionic liquid type in the examples and comparative examples

[0035] Example 6 Solution Preparation 1. Preparation of standard solutions Table 5. Preparation of Standard Solutions

[0036] The solvent used to prepare the solution is methanol, and the solution is stored in a refrigerator.

[0037] 2. Preparation of working fluid Table 6. Preparation of working solution

[0038] Example 7: HS-SPME-GC-MS Operation Procedures 1. HS-SPME Operation Add 10.00 mL of saturated NaCl to a 15.00 mL extraction flask, add a stir bar, then add 2.4 mL of standard solution, seal with plastic wrap, plug with a rubber cap, and then seal with an aluminum cap. Then proceed with the extraction (insert the extraction head first and then push it out).

[0039] 2. GC-MS Operations After HS-SPME is completed, retract the extraction head, pull out the injection needle, insert it into the GC-MS, push out the extraction head, analyze for 3 minutes, retract the extraction head, and then pull it out from the GC injection port for analysis.

[0040] 3. GC condition parameters Table 7 GC Conditions

[0041] Table 8 MS Condition Parameters

[0042] Example 1 (I) Voltammetric behavior of extraction coatings prepared by electropolymerization Solid-phase microextraction heads were prepared using cyclic voltammetry, and their CV spectra were recorded as follows: Figure 1 (A: 11,12-dihydroindolo[2,3-a]carbazole; B: carbazole; C: indole; D: A+BMIMPF6; E: A+BOP; F: A+C16MIMPF6; G: A+OMIMPF6; H: A+PMIMPF6)).

[0043] 1. Voltammetric behavior of the extraction head without the addition of ionic liquid The CV curves of the coatings obtained from cyclic voltammetry scanning of comparative examples 1-3 were respectively... Figure 1 -A、 Figure 1 -B and Figure 1 -C. From Figure 1 In Figure -A, two oxidation peaks appear at approximately 1.4 V and 1.6 V, respectively, with the second peak showing a significantly higher current than the first. As the number of polymerization cycles increases, the peak current decreases and then increases, which is related to the presence of both indole and carbazole in the monomer. Simultaneously, it can be observed visually that the coating thickness on the metal surface gradually increases and the color deepens with increasing polymerization cycles. After 50 polymerization cycles, a black coating is observed on the steel wire surface, indicating successful coating preparation. (From the figure...) Figure 1 -B and Figure 1As can be seen from the -C curve, both indole and carbazole show only one oxidation peak in their CV spectra. This is because their structures contain only one monomer.

[0044] 2. Using 11,12-dihydroindolo[2,3-a]carbazole as the polymerization monomer, and adding 5 different ILs under the same conditions, the CV curves of Examples 1-5 were analyzed.

[0045] CV curves during electrochemical coating preparation are as follows Figure 1 -D、 Figure 1 -E、 Figure 1 -F、 Figure 1 -G、 Figure 1 -E represents the CV diagrams for ILs doped with BMIMPF6, BOP, C16MIMPF6, OMIMPF6, PMIMPF6, etc. Compared with those without IL, IL affects its electrochemical behavior, which in turn affects its microstructure.

[0046] Example 2: Microscopic morphology characterization of different types of solid-phase microextraction heads 1. SEM image of polymerized 11,12-dihydroindolo[2,3-a]carbazole The resulting coating was characterized microscopically using SEM. SEM images of the polymerized coating with electrochemical deposition potentials ranging from 0 to 2.0 V, using 11,12-dihydroindolo[2,3-a]carbazole as the polymerization monomer, are shown below. Figure 2 As shown. From Figure 2 As can be seen from -A, the resulting polymer coating contains two different structures: one dominated by larger particles and the other dominated by smaller particles; at its low magnification... Figure 2 -B shows that an uneven coating is formed on the surface of the steel wire, exhibiting two distinct structures: smaller particles adhere to the larger particles in the coating. This indicates that using only 11,12-dihydroindolo[2,3-a]carbazole as a monomer, two distinct polymeric coatings can be obtained on the metal surface, which is closely related to the two typical oxidation peaks generated on the metal wire surface.

[0047] 2. SEM image of polymerized indole SEM images of polymer coatings with electrochemical deposition potentials ranging from 0 to 2.0 V, using indole as the polymerization monomer. Figure 3 The coating has a relatively smooth particle shape; at its low magnification... Figure 3 In -B, it can be observed that the resulting coating is smoother than that of polymerized 11,12-dihydroindolo[2,3-a]carbazole, and mainly consists of large particles.

[0048] 3. SEM image of polymeric carbazole SEM images of polymer coatings with electrochemical deposition potentials in the range of 0-2.0 V, using carbazole as the polymerization monomer. Figure 4 ).from Figure 4 As can be seen from -A, the particle size of the coating is relatively uniform, and... Figure 3 -A particles are smaller; at its lower magnification... Figure 4 In -B, it can be observed that the resulting coating is relatively loose, and the connection between particles is not tight.

[0049] 4. SEM image of the coating obtained by doping with BMIMPF6 When 11,12-dihydroindolo[2,3-a]carbazole is used as the polymerization monomer, the SEM image of the polymer coating after adding BMIMPF6 to the electrolyte is shown below. Figure 5 As shown. Figure 5 -B and Figure 2 -A coatings exhibit a denser structure with closely bonded particles of varying sizes, as seen in low-magnification structures ( Figure 5 -B) It can be seen that two typical structures can be clearly observed in the polymerized coating, relative to Figure 2 -B has a significantly increased number of small polymer particles attached to it.

[0050] 5. SEM image of the coating obtained by doping with BOP When 11,12-dihydroindodo[2,3-a]carbazole is used as the polymerization monomer, after adding BOP to its electrolyte, the SEM image of the polymer coating is shown. Figure 6 ).from Figure 6 As can be seen in Figure 5-A, the coating particles are more distinct than those in Figure 5-A, with more large polymers present in its low-magnification structure. Figure 6 -B reveals two different coating structures, in which fewer small particles are attached and more concentrated.

[0051] 6. SEM image of the coating obtained by doping C16MIMPF6 When 11,12-dihydroindolo[2,3-a]carbazole is used as the polymerization monomer, and C16MIMPF6 is added to its electrolyte, the SEM image of the resulting polymer coating is obtained. Figure 7 ).from Figure 7 As can be seen from -A, the resulting coating particles are not obvious, and the large aggregated particles are relatively coarse, as observed from the low-magnification structure. Figure 7 In -B, it can be seen that both polymer structures are clearly visible, and their attached small particles are relatively... Figure 2 -B、 Figure 5 -B、 Figure 6 -B、 Figure 8 -B、 Figure 9 -B is the most abundant and evenly distributed.

[0052] 7. SEM image of the coating obtained by doping with OMIMPF6 When 11,12-dihydroindolo[2,3-a]carbazole is used as the polymerization monomer, and OMIMPF6 is added to its electrolyte, the resulting polymer coating is shown in the SEM image. Figure 8 ),from Figure 8 As can be seen from -A, the coating consists of many small particles aggregated into large sheet-like particles; from the low magnification structure ( Figure 8 In -B), the two coating structures are closely bonded, and the attached particles are not obvious.

[0053] 8. SEM image of the coating obtained by doping PMIMPF6 When 11,12-dihydroindolo[2,3-a]carbazole is used as the polymerization monomer, the structure of the resulting polymer coating after adding PMIMPF6 to the electrolyte is as follows. Figure 9 As shown. Observation Figure 9 -A, the structure of its coating is similar to Figure 4 -A is similar, both being uniform particles. From low magnification Figure 9 In -B, the two structures are closely linked, and... Figure 4 -B coatings are denser than traditional coatings.

[0054] Example 3: Effect of different comonomers on peak area The experiment investigated the response of indole, carbazole, and 11,12-dihydroindolo[2,3-a]carbazole copolymer to the peak area of ​​phenols. Figure 10 As shown, (1 is polymeric indole, 2 is polymeric carbazole, and 3 is polymeric 11,12-dihydroindolo[2,3-a]carbazole) the experimental results show that the polymeric dimonomer 11,12-dihydroindolo[2,3-a]carbazole is more sensitive to phenols than polymeric indole and polymeric carbazole.

[0055] Example 4: Effect of different ionic liquids on peak area The experiment investigated the effect of five types of extraction heads on the peak area of ​​phenols. The results showed that... Figure 11As shown (1 is 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 2 is 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonylimide (BOP), 3 is 1-hexadecyl-3-methylimidazolium hexafluorophosphate (C16MIMPF6), 4 is 1-octyl-3-methylimidazolium hexafluorophosphate (OMIMPF6), and 5 is 1-propyl-3-methylimidazolium hexafluorophosphate ([PMIm]PF6)), the extraction head doped with C16MIMPF6 exhibited the highest peak area and showed the best adsorption effect compared to the other four. Therefore, the coating prepared with C16MIMPF6 salt was used as the extraction head in the experiment, and the extraction time, stirring rate, and desorption time were optimized.

[0056] Example 5: Optimization of Headspace Solid-Phase Microextraction Conditions Using the C16MIMPF6 doped coating prepared in Example 1 as the extraction head, six phenolic compounds were detected by HS-SPME-GC-MS. The extraction time, stirring rate, extraction temperature and desorption time were optimized.

[0057] Extraction time optimization: The response of the constructed method to the target peak when the extraction time is 10-40 min. Figure 12 As shown, when the extraction time is less than 30 min, the peak area is directly proportional to the extraction time, and the response peak is the largest relative to other times. Therefore, the optimal extraction time is 30 min.

[0058] Stirring rate optimization: The response of the constructed method to the target peak was investigated when the stirring speed varied within the range of 300 r / min–700 r / min. Figure 13 It can be seen that the peak area is the largest when the stirring speed is 500 r / min. Therefore, the optimal extraction rate is 500 r / min.

[0059] Extraction temperature optimization: The response of the constructed method to the target peak at extraction temperatures of 20-60 ℃. Figure 14 It can be seen that the peak area is the largest at 40 ℃, therefore the optimal extraction temperature is 40 ℃. Desorption time optimization: When the resolution time is 1-5 min, the response of the constructed method to the target peak is optimized. Figure 15 It can be seen that the peak area of ​​the response is optimal when the resolution time is 3 minutes. Therefore, 3 minutes is chosen as the optimal resolution time.

[0060] GC-MS Analysis Conditions: A Shimadzu GC-MS-QP2010 gas chromatograph-mass spectrometer was used. Chromatographic conditions: HP-5MS capillary column (30 m x 0.25 mm x 0.25 μm), column oven temperature 60°C, injection port temperature 200°C, splitless injection, pressure 89.7 kPa, total flow rate 63.5 mL / min, column flow rate 1.45 mL / min, linear velocity 43.9 cm / s, purge flow rate 3.0 mL / min. Mass spectrometry conditions: ion source temperature 200°C, interface temperature 230°C, solvent delay time 3 min, scan range m / z 50-500.

[0061] Effect Example 6: Linearity of the Method To evaluate the performance of the method under optimized conditions, solutions of the 10 μg / L mixed standard were prepared at concentrations of 0.50 μg / mL, 1.00 μg / mL, 1.50 μg / mL, 2.00 μg / mL, and 2.50 μg / mL. These solutions were then subjected to HS-SPME using the optimized method, followed by GC-MS analysis. Figure 16 As can be seen, for the six phenolic compounds, the response peak area is directly proportional to the concentration and has a good linear response.

[0062] Example 7: Detection of actual samples Soil samples from Mingtan were used as samples, and optimized conditions were applied for analysis, with the recovery rate determined. Sample pretreatment: Soil samples were collected in beakers, dried, and then 10 g of the sample was dissolved in 50 mL of methanol. After sonication for 30 min, the solution was filtered, and NaCl was added to the filtrate until saturation. 5 mL of the treated filtrate was transferred to a 15 mL headspace extraction bottle for headspace extraction. After extraction, the extraction head was retracted into the injection needle and then withdrawn. The injection needle was then inserted into a GC-MS sample for analysis. Experimental results showed that no phenolic substances were detected in the sample. To further evaluate the assay method, the same extraction head was used to spike the sample for recovery. The recovery rates are shown in Table 9. Table 9 Spiked Recycling

[0063] This application uses 11,12-dihydroindolo[2,3-a]carbazole as a comonomer and ionic liquid as a dopant to prepare a coating on the surface of stainless steel wire. The effects of different ionic liquids (ILs) on the microstructure and extraction yield of the coating were investigated. The optimal extraction conditions were determined to be: stirring rate 500 r / min, extraction temperature 40 ℃, extraction time 30 min, and settling time 3 min. Under these optimal conditions, 1-hexadecyl-3-methylimidazolium hexafluorophosphate (C16MIMPF6) was selected as the optimal extraction head. A combined HS-SPME and GC-MS technique was established for the analysis and detection of 3-chloro-4-fluorophenol, 2,6-tert-butyl-4-methylphenol, 4-aminophenol, 2,4,6-trichlorophenol, and 4-chloro-3,5-dimethylphenol in soil. The results showed that the IL-doped extraction head had a significantly higher response to phenolic compounds than the copolymer containing only 11,12-dihydroindolo[2,3-a]carbazole.

[0064] Based on the above-described preferred embodiments according to this application, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a solid-phase microextraction coating, characterized in that, Includes the following steps: S1: Constructing a three-electrode system: Pre-treated stainless steel wire is used as the working electrode; Ag / AgCl was used as the reference electrode, and platinum wire was used as the auxiliary electrode. S2: An electrolyte is prepared by dissolving the functional monomer, electrolyte and dopant in acetonitrile solvent using 11,12-dihydroindolo[2,3-a]carbazole as the functional monomer, tetrabutylammonium perchlorate as the electrolyte, hexafluorophosphate ionic liquid as the dopant. S3: Apply current to the three-electrode system and electrochemically polymerize the stainless steel wire surface using cyclic voltammetry to prepare the solid-phase microextraction coating. S4: Perform programmed temperature aging on the coating; S5: Assemble the coating onto the solid phase microextraction injector.

2. The method according to claim 1, characterized in that, The ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonylimide salt, 1-hexadecyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium hexafluorophosphate, and 1-propyl-3-methylimidazolium hexafluorophosphate.

3. The method according to claim 2, characterized in that, The ionic liquid is 1-hexadecyl-3-methylimidazolium hexafluorophosphate.

4. The method according to claim 1, characterized in that, The parameters for the cyclic voltammetry method are: initial potential 0.0 V, high potential 2.0 V, scan rate 0.05 V / s, number of scan segments 50, and sensitivity 1×10⁻⁶. - ³A / V.

5. The method according to claim 1, characterized in that, The electrolyte contains 0.008 mol / L of 11,12-dihydroindolo[2,3-a]carbazole monomer, 5 μg / mL of ionic liquid, and 0.1 mol / L of tetrabutylammonium perchlorate.

6. The method according to claim 1, characterized in that, The programmed temperature aging process is as follows: from 20 °C to 110 °C in 25 min, held at 110 °C for 65 min, and then increased to 260 °C in 90 min.

7. A solid-phase microextraction coating prepared by the method of any one of claims 1-6, said coating containing ionic liquid-doped polymeric 11,12-dihydroindolo[2,3-a]carbazole.

8. A method for detecting phenolic compounds using a solid-phase microextraction coating as described in claim 7, characterized in that... Includes the following steps: (1) Insert the solid phase microextraction injector into the extraction bottle containing the phenolic compound sample for headspace solid phase microextraction. The extraction conditions are: extraction time 10-40 min, stirring rate 300-700 r / min, extraction temperature 20-60 ℃, and elution time 1-5 min. (2) After extraction, the sample injector is inserted into the gas chromatograph-mass spectrometer for analysis and detection.

9. The method according to claim 8, characterized in that, The headspace solid-phase microextraction conditions were as follows: extraction time 30 min, stirring rate 500 r / min, extraction temperature 40 ℃, and desorption time 3 min.

10. The method according to claim 8, characterized in that, The phenolic compound is one or more of 2,4,6-trichlorophenol, 3-chloro-4-fluorophenol, 3-aminophenol, 2,6-di-tert-butyl-4-aminophenol, 4-aminophenol, and 4-chloro-3,5-dimethylphenol.

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