Extraction head and detection method using same

Abstract

The invention discloses a method for preparing a polymerized 6-bromoindole-IL-aminated graphene octadecylamine modified-nitrogen doped graphene-multi-walled carbon nanotube coating on the surface of a stainless steel wire by utilizing a cyclic voltammetry method. A method for detecting malathion residues in fresh vegetables or fruits and a method for detecting phenolic compounds in a water environment are constructed by adopting a headspace extraction technology and combining gas chromatography-mass spectrometry (GC-MS). The established analysis method has good linear response to phenolic substances and malathion, and the established analysis method is used for detecting malathion residues in fresh vegetables or fruits and analyzing phenolic compounds in water samples. Wherein the adding standard recovery rate of the pear synthase water sample is between 99.6% and 100.3%, and the adding standard recovery rate of the pear synthase water sample is between 99.7% and 100.3%, so that the method has relatively good practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the fields of electrochemistry, environmental analysis and food safety, and particularly relates to an extraction head and a detection method using the same. BACKGROUND

[0002] With the rapid development of chemical industry, organic pesticides, polychlorinated biphenyls, halogenated aromatic hydrocarbons and phenols and the like are released into the environment in large quantities, resulting in water environmental pollution and threatening human health. In particular, the pollution of phenolic compounds and organophosphorus compounds has also attracted more and more attention. The detection of these pollutants in the prior art has the problems of complex sample pretreatment process, tedious operation, long processing time, and expensive instruments, making it difficult to be widely promoted. Therefore, it is necessary to study an electrochemical method with simple operation, rapid and efficient, and high sensitivity. SUMMARY

[0003] To solve one or more of the above problems, an extraction head and a method for detecting phenols and malathion using the same are provided.

[0004] According to one aspect of the present application, an extraction head for detecting benzene compounds is characterized in that the extraction head is a composite material of 6-Brin-Ofg-[AyttP][PF6]-MWCN.

[0005] In some embodiments, the method for preparing the extraction head comprises: configuring a mixed solution of 6-Brin as a monomer, [AyttP][PF6] as an ionic liquid, Ofg and MWCN as co-doped materials, acetonitrile as a solvent, and tetrabutylammonium perchlorate as an electrolyte; inserting an electrode system into the mixed solution to prepare a composite extraction head by cyclic voltammetry.

[0006] In some embodiments, the concentration of 6-Brin is 0.015 mol / mL, the concentration of Ofg is 0.20 mg / mL, the concentration of MWCN is 0.20 mg / mL, and the concentration of [AyttP][PF6] is 10.0 μg / mL.

[0007] In some embodiments, the electrode system is: Ag / AgCl as a reference electrode; platinum wire as an auxiliary electrode; and stainless steel wire as a working electrode.

[0008] According to another aspect of the present application, a detection method for phenolic compounds is provided, comprising the following steps: headspace extraction of phenolic compounds using the extraction head of claims 1-4; constructing a gas chromatography-mass spectrometer and detecting phenolic compounds using the extraction head.

[0009] In some embodiments, the composite extraction head headspace extraction of phenolic compounds comprises the following steps: Prepare a phenolic standard solution; Prepare a phenolic working solution; Perform the HS-SPME operation: add saturated sodium chloride solution and phenolic standard solution in the extraction bottle to form a first mixed solution; perform water bath heating and stirring on the first mixed solution; insert the sampling device into the headspace extraction bottle, and expose the extraction head of the sampling device to the upper part of the extraction bottle for headspace extraction; After completion, perform the GC-MS operation: After the HS-SPME operation step is completed, Retract the extraction head into the protective sleeve, quickly insert it into the GC-MS sampling port, and then perform GC-MS separation and detection after analysis.

[0010] In some embodiments, the temperature of the constant temperature magnetic stirrer is set to 50 ℃, the stirring speed is 600 r / min, and the headspace extraction is performed for 30 min.

[0011] According to another aspect of the present application, a method for detecting malathion is provided, characterized in that it comprises the following steps: Headspace extraction of malathion is performed using the extraction head of claims 1-4; Construct a gas chromatography-mass spectrometer, and use the extraction head to detect malathion.

[0012] In some embodiments, the composite extraction head headspace extraction of malathion comprises the following steps: Prepare a malathion standard solution; Prepare a malathion working solution; Perform the HS-SPME operation: add saturated sodium chloride solution and malathion standard solution in the extraction bottle to form a first mixed solution; perform water bath heating and stirring on the first mixed solution; insert the sampling device into the headspace extraction bottle, and expose the extraction head of the sampling device to the upper part of the extraction bottle for headspace extraction; After completion, perform the GC-MS operation: After the HS-SPME operation step is completed, Retract the extraction head into the protective sleeve, quickly insert it into the GC-MS sampling port, and then perform GC-MS separation and detection after analysis.

[0013] The beneficial effects are: an effective high selectivity sample and high sensitivity sample pretreatment method is established, and then the content of organic pollution in the environment is determined. The polymer-coated extraction head prepared by the technical scheme has good adsorption, good mechanical stability, and good sensitivity.

[0014] In some embodiments, the temperature of the constant temperature magnetic stirrer is set to 60℃, the stirring speed is 300 r / min, and the headspace extraction is performed for 40 min.

[0015] Compared with the prior art, the present application has the following beneficial effects: The present application uses 6-bromoindole (6-Brin) as a monomer, ionic liquid (7-azabenzotriazol-1-yloxy) tris (trimethylamino) phosphonium hexafluorophosphate [AyttP] [PF6], octadecylamine aminated graphene (Ofg), and multi-walled carbon nanotubes (MWCN) as co-doped materials. A polymeric 6-bromoindole-IL-aminated graphene octadecylamine modified-nitrogen-doped graphene-multi-walled carbon nanotube coating is prepared on the surface of a stainless steel wire by cyclic voltammetry. A method for detecting malathion residues in fresh vegetables or fruits and a method for detecting phenolic compounds in water environment are constructed by using headspace extraction technology combined with gas chromatography-mass spectrometry (GC-MS). The extraction head prepared by the technical scheme of the present application has good adsorption, good mechanical stability, and good sensitivity. The analysis method constructed has good linear response to phenolic substances and malathion. The analysis method established is used to detect malathion residues in fresh vegetables or fruits and analyze phenolic compounds in water samples. The standard addition recovery rates of pear and water samples are 99.6% - 100.3% and 99.7% - 100.3%, respectively, indicating that this method has good practicability. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of the preparation process of the extraction head in the present application; Figure 2 is the voltammetric behavior of the 6-Brin coating in the present application; Figure 3 is the voltammetric behavior of the P(6-Brin)-[AyttP][PF6] coating in the present application; Figure 4 is the voltammetric behavior of the P(6-Brin)-Ofg-MWCZ extraction head in the present application; Figure 5 is the voltammetric behavior of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ extraction head in the present application; Figure 6 is the SEM image of the 6-Brin coating in the present application; Figure 7 is the SEM image of the 6-Brin coating in the present application; Figure 8 is the SEM image of the 6-Brin coating in the present application; Figure 9is a SEM image of the 6-Brin coating in this application; Figure 10 is a SEM of the P(6-Brin)-Ofg-MWCZ coating in this application; Figure 11 is a SEM of the P(6-Brin)-Ofg-MWCZ coating in this application; Figure 12 is a SEM of the P(6-Brin)-Ofg-MWCZ coating in this application; Figure 13 is a SEM of the P(6-Brin)-Ofg-MWCZ coating in this application; Figure 14 is a SEM image of the P(6-Brin)-[AyttP][PF6] coating in this application; Figure 15 is a SEM image of the P(6-Brin)-[AyttP][PF6] coating in this application; Figure 16 is a SEM image of the P(6-Brin)-[AyttP][PF6] coating in this application; Figure 17 is a SEM image of the P(6-Brin)-[AyttP][PF6] coating in this application; Figure 18 is a SEM image of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ modification in this application; Figure 19 is a SEM image of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ modification in this application; Figure 20 is a SEM image of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ modification in this application; Figure 21 is a SEM image of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ modification in this application; Figure 22 is a SEM image of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ modification in this application; Figure 23 is a SEM image of the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ modification in this application; Figure 24 is a plot of peak area response of the extraction head to the analyte after varying the concentration of the ionic liquid in this application; Figure 25Figure 1 is a peak area response plot of the extraction head to the analyte after varying the concentration of octadecylamine functionalized graphene in the present application; Figure 26 Figure 2 is a peak area response plot of the extraction head to the analyte after varying the extraction temperature in the present application; Figure 27 Figure 3 is a peak area response plot of the extraction head to the analyte after varying the extraction time in the present application; Figure 28 Figure 4 is a peak area response plot of the extraction head to the analyte after varying the analysis time in the present application; Figure 29 Figure 5 is a standard curve of phenolic compounds in the present application; Figure 30 Figure 6 is a standard curve of malathion in the present application; Figure 31 Figure 7 is a chromatogram of water-spiked-phenolic compounds in the present application; Figure 32 Figure 8 is a chromatogram of pear-spiked-malathion in the present application; Figure 33 Figure 9 is a linear correlation of water-spiked-recovery in the present application; Figure 34 Figure 10 is a linear correlation of pear-spiked-recovery in the present application. DETAILED DESCRIPTION

[0017] The present application will be further described below in conjunction with the accompanying drawings.

[0018] I. Reagents and Instruments Table 1 - Instruments and Models

[0019] Table 2 - Experimental Reagents

[0020] II. GC / MS Condition Settings Table 3 - GC Conditions for Phenolic Compounds

[0021] Table 4 - Oven Temperature Program Settings for Phenolic Compounds

[0022] MS Conditions: Ion Source (EI) Temperature 200 °C; Interface Temperature 250 °C.

[0023] Table 5 - GC Conditions for Malathion

[0024] Table 6 - Oven Temperature Program Settings for Malathion

[0025] MS conditions: Ion source temperature (EI) 200 °C; interface temperature 250 °C, hold for 2 min, ramp to 280 °C at 20 °C / min, hold for 8 min.

[0026] Table 7 - Selected ions for the four test substances

[0027] III. Preparation of different types of extraction heads (I) Preparation of working electrode Take 1.6-1.8 cm stainless steel wire, and use a ruler to polish the cut steel wire to be smooth and straight, then first ultrasonic clean with water and nitric acid in a ratio of 1:1 for 5 min, ultrasonic clean with Aesop water for 5 min (wash twice), then ultrasonic clean twice with anhydrous ethanol, place in a beaker, cover with plastic wrap for standby.

[0028] (II) Polymerization of composite SPME extraction head An electrochemical polymerization SPME extraction head was used, the working electrode was made of 1.6-1.8 cm stainless steel wire, the auxiliary electrode was made of platinum wire electrode, and the reference electrode was made of saturated calomel electrode, and assembled into a single-cell three-electrode mode. The three electrodes were slowly immersed into an acetonitrile electrolyte containing 0.015 mol / mL 6-bromoindole (6-Brin), 0.20 mg / mL octadecylamine amino graphene (Ofg), 0.20 mg / mL multi-walled carbon nanotubes (MWCN), 10.0 μg / mL (7-azatryptophan-1-yl oxo) tris (trimethylamino) phosphine hexafluorophosphate [AyttP] [PF6] and 0.05 mol / L tetrabutylammonium perchlorate (TBAP), as shown in the process. Then, the prepared 6-Brin-Ofg-[AyttP] [PF6]-MWCN SPME head was taken out. After aging, the extraction head was stuck on the sample injector with a mixed resin of epoxy resin and polyamide resin in a ratio of 1:1, and placed overnight to dry, then standby. Figure 1

[0029] IV. Preparation of solutions (I) Preparation of malathion standard solution Take a 10 mg bottle of malathion, dissolve in methanol, then transfer to a 10 mL volumetric flask, and dilute to the mark with methanol to obtain a 1.0 mg / mL standard solution.

[0030] (II) Preparation of phenolics standard solution ​Accurately weigh 0.1000 g of 3-chloro-4-fluorophenol, 2,6-dimethoxyphenol, 4-chloro-3,5-dimethylphenol into a beaker, dissolve with methanol, transfer to a 100.00 mL volumetric flask, dilute to the mark with methanol to obtain a mixed standard solution of 1.0 mg / mL.

[0031] V. Headspace extraction operation Transfer 9.50 mL of saturated sodium chloride solution into a 15.00 mL headspace extraction bottle, add a magnetic stirrer, add 0.50 mL of 1.0 mg / mL mixed solution, seal with a rubber plug and an aluminum cap after sealing with a rubber plug, and place on a constant temperature water bath magnetic stirrer. When the conditions reach the set value, insert the sampler into the extraction bottle, push out the coated extraction head so that the coating is completely above the solution.

[0032] Phenolic headspace extraction conditions: the temperature of S10-3 is set to 50℃, the stirring speed is 600 r / min, and the headspace extraction is 30 min.

[0033] Malathion headspace extraction conditions: the temperature of S10-3 is set to 60℃, the stirring speed is 300 r / min, and the headspace extraction is 40 min. After completion, pull the extraction head back into the protective sleeve, directly insert into the GC-MS sample port, and analyze and detect after 3 min of analysis.

[0034] VI. Result characterization (1) CV diagram of each extraction head The SPME head was prepared by electrochemical method, and the optimal potential for preparing P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ coated extraction head was 1.1 V - 1.9 V, and the CV diagram of the preparation process was recorded (see Figures 2-5 ).

[0035] Figure 2 The CV scan was performed with an electrolyte containing 0.015 mol / L of 6-Brin. It can be observed that at a potential of 1.65 V, 6-Brin has a obvious oxidation peak, indicating that 6-Brin is obviously oxidized at this potential, and a polymer is generated on the steel wire surface, and the thickness of the coating increases with the increase of the number of scanning circles, but the peak current decreases with the increase of the number of scanning circles, which may be related to the decrease of the conductivity with the increase of the thickness of the coating.

[0036] Figure 3CV curve of 6-Brin with 10 μg / mL of [AyttP][PF6] and 0.2 mg / mL of Ofg in acetonitrile. From the figure, it can be seen that the first circle still appears an obvious oxidation peak at about 1.55 V, and the potential also moves to the negative potential compared with the case of only containing monomer.

[0037] Figure 4 CV curve of 6-Brin with 10 μg / mL of [AyttP][PF6] and 0.2 mg / mL of Ofg in acetonitrile. From the figure, it can be seen that the first circle still appears an obvious oxidation peak at about 1.55 V, and the potential also moves to the negative potential compared with the case of only containing monomer.

[0038] Figure 5 CV curve of 6-Brin with 10 μg / mL of [AyttP][PF6], 0.2 mg / mL of Ofg and 0.2 mg / mL of MWCZ in acetonitrile. From the figure, it can be seen that after adding the ionic liquid and the amino-functionalized graphene octadecylamine, the solution conductivity is enhanced, and the CV curve is more uniform than that of Figure 2 、 Figure 3 、 Figure 4 the CV curve of 6-Brin with 10 μg / mL of [AyttP][PF6], 0.2 mg / mL of Ofg and 0.2 mg / mL of MWCZ in acetonitrile. From the figure, it can be seen that after adding the ionic liquid and the amino-functionalized graphene octadecylamine, the solution conductivity is enhanced, and the CV curve is more uniform than that of

[0039] (II) Micro-morphology of the polymerized SPME coating 1. Micro-morphology characterization of the 6-Brin coating To some extent, the microstructure of the coating determines the extraction capacity of the coating. From the SEM image of the polymerized 6-Brin coating in Figures 6-9 it can be observed that the polymerized film has a membrane structure, and the coating is dense with a few cracks. Figure 6 It can be seen from the SEM image in Figure 7 that the polymerized film has a corrugated shape and is tightly attached to the steel wire surface, as shown in Figure 8 From other images in Figure 9 , it can be seen that the thickness of the polymerized 6-Brin coating is about 5 μm, and the coating is relatively thin and uniform. Figure 8 In addition, the SEM image of the cross-section of the polymerized 6-Brin coating was observed, as shown in Figure 9 , and it can be observed that the thickness of the polymerized film is relatively uniform.

[0040] 2. Micro-morphology characterization of P(6-Brin)-Ofg-MWCZ coating Figure 10 The SEM image of the composite coating modified by 6-Brin and aminated graphene octadecylamine for electro-polymerization shows that the coating is dense, but compared with the polymerized Brin, the coating has granular polymer monomers and a three-dimensional porous structure Figure 11 ), and becomes more uniform, and the coating has very good adhesion Figure 12 and Figure 13 , which may be due to the addition of aminated graphene octadecylamine modification to the coating, which effectively improves the microstructure of the coating.

[0041] 3. Micro-morphology characterization of P(6-Brin)-[AyttP][PF6] coating Figures 14-17 The SEM image of the coating obtained by adding [AyttP][PF6] to the electrolyte containing 6-Brin monomers shows that compared with the polymerized Brin, the structure has changed greatly, has a three-dimensional porous structure, and the polymerization presents a chain-like growth Figure 14 ), and the more obvious three-dimensional structure is observed in the low-magnification SEM image of the coating Figure 15 ), the coating is thin but uniformly distributed, and grows closely to the surface of the steel wire Figure 16 and Figure 17 .

[0042] 4. Micro-morphology characterization of P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ coating As shown in Figures 18-23 , when Ofg and MWCZ are doped in the coating at the same time, the P(6-Brin)-[AyttP][PF6]-Ofg-MWCZ coating presents a granular film structure, has a large effective specific surface area, and has a porous network structure in the microstructure and a large number of pores; the coating is thick and not easy to fall off, and a more dense and stable coating is obtained, which is beneficial to extraction.

[0043] (Three) Influence of the concentration of ionic liquid When other conditions are unchanged, the influence of the concentration of IL ([AyttP][PF6]) on the response peak area of phenolic substances and malathion was investigated. The results are shown in Figure 24As shown, when the concentration of IL in the electrolysis is 6-10 μg / mL, the response of the composite coating gradually increases with the increase of IL addition, that is, the response increases with the increase of concentration; however, when the concentration exceeds 10 μg / mL, the response decreases with the increase of concentration, and the whole process shows a downward trend. The reason for this is that too much IL fills the voids in poly(6-bromoindole-octadecylamine-aminographene-multi-walled carbon nanotubes), causing the original space to be occupied. At the same time, the high viscosity of IL, to a certain extent, hinders the copolymerization of 6-bromoindole-octadecylamine-aminographene-multi-walled carbon nanotubes and leads to a decrease in the dispersion of carbon materials in the electrolyte solution, ultimately affecting the size of the response peak area. Therefore, the amount of ionic liquid added during the preparation of the composite coating is 10 μg / mL.

[0044] (iv) Effect of octadecylamine aminographene concentration With other conditions remaining constant, the experiment investigated the response of octadecylamine-aminographene concentrations (0.1-0.8 mg / mL) to phenolic substances and malathion surface area. Figure 25 As shown, when the concentration of octadecylamine-aminographene is 0.2 mg / mL, the response peak areas of phenolic substances and malathion are the largest. After that, as the concentration of octadecylamine-aminographene increases, the response peak areas of the target analytes continuously decrease. This is because as the concentration of octadecylamine-aminographene increases, its effective concentration in the electrolyte solution decreases, causing most of the octadecylamine-aminographene to be deposited in the electrolyte solution during electropolymerization.

[0045] (v) Optimization of headspace extraction conditions 1. Optimization of extraction temperature As temperature increases, the volatility of the analyte increases, and the vapor pressure of the gas phase in the headspace vial increases, which promotes the adsorption process of the coating and reduces the adsorption capacity of the analyte on the extraction head; thus, the sensitivity of the extraction head decreases when detecting the target analyte.

[0046] With other conditions remaining constant, this experiment investigated the effect of extraction temperature variations from 30-70℃ on the peak area of ​​phenolic substances and malathion. Figure 26 As shown, the extraction efficiency of phenols was highest at 50 °C, while that of malathion was highest at 60 °C. Further increases in temperature resulted in a decrease in extraction efficiency, which is related to the properties of the extraction head prepared in the experiment, the volatility of the target analyte, and the set temperature. Therefore, it is necessary to analyze and optimize the extraction conditions of the prepared extraction head. Thus, the optimal extraction temperature for phenols in this experiment was 50 °C, and the optimal extraction temperature for malathion was 60 °C.

[0047] 2. Optimization of extraction time With other conditions remaining constant, this experiment investigated the effect of extraction time variations from 10 to 50 min on the peak area of ​​phenolic substances and malathion. Figure 27 As can be seen, the peak area gradually increases with the increase of extraction time; the peak area of ​​phenolic substances is the largest at 30 min, and that of malathion is the largest at 40 min; when the extraction time is further increased, the peak area decreases again. This is because after reaching the optimal extraction time, the adsorbed substances will be desorbed again, and water droplets will be adsorbed on the surface of the extraction coating, which will not be effective. Therefore, the optimal extraction time for phenolic substances in this experiment is 30 min, and the optimal extraction time for malathion is 40 min.

[0048] 3. Optimization of parsing time With other conditions remaining constant, this experiment investigated the effect of desorption time variations from 1 to 5 minutes on the peak area of ​​phenolic substances and malathion. Figure 28 The results show that the peak area is largest when the desorption time is 3 min, which is likely related to the properties of phenolic substances and malathion. Therefore, the optimal desorption time for phenolic substances and malathion in this experiment is 3 min.

[0049] (vi) Analytical performance Using optimized conditions, phenolic substances and malathion at concentrations of 10-50 μg / mL were analyzed. Figures 29-30 It can be seen that as the concentration increases, the peak area also increases, and there is a good linear correlation, indicating good sensitivity. This suggests that the analytical method has good linear correlation.

[0050] (vii) Analysis and testing of actual samples To verify its practicality, the above methods were applied to analyze and test actual samples; the actual samples used were lake water from a famous pond for phenol testing and fresh pears for malathion testing. For example... Figures 31-34 As shown.

[0051] Under optimized experimental conditions, 3-chloro-4-fluorophenol, 4-chloro-3,5-dimethylphenol, and 2,6-dimethoxyphenol were analyzed and determined in the water of Youmingtan. The results showed that the target analytes were not detected. To further evaluate the assay method, a spiked recovery experiment was performed on the water samples at concentrations of 30 μg / mL, 40 μg / mL, and 50 μg / mL. All three target analytes were detected in the spiked samples, as shown in the chromatograms. Figure 31 As shown, with increasing spike concentration, the peak areas of the extraction head for the three target analytes continuously increase, indicating that this method can be used for the detection of 3-chloro-4-fluorophenol, 4-chloro-3,5-dimethylphenol, and 2,6-dimethoxyphenol in water samples.Figure 33 As shown in Table 8, the spiked recovery of the samples exhibited a good linear correlation. The spiked recovery rate of the water samples ranged from 96.6% to 100.3%, indicating that this method is practical.

[0052] Under optimized experimental conditions, the malathion content in pears from a school supermarket was analyzed and determined; the results showed that the target analyte was not detected. To further evaluate the assay method, spiked recovery experiments were performed on the treated pear samples at spiked concentrations of 30 μg / mL, 40 μg / mL, and 50 μg / mL. Malathion was detected in all spiked samples, as shown in the chromatograms below. Figure 32 As shown, the peak area of ​​the extraction head's response to malathion continuously increases with increasing spike concentration, indicating that this method can be used for the detection of malathion in pear samples. Figure 34 As shown in Table 9, the spiked recovery of the samples exhibited a good linear correlation. The spiked recovery rate of pear was between 99.7% and 100.3%, indicating that this method is practical.

[0053] Table 8 Water-Spike Recovery Rate

[0054] Table 9. Pear - Spiked Recovery Rate

[0055] This experiment used 6-bromoindole (6-Brin) as the monomer and ionic liquid (7-azabenzotriazol-1-yloxo)tris(trimethylamino)phosphine hexafluorophosphate [AyttP][PF6], octadecylamine-modified graphene (Ofg), and multi-walled carbon nanotubes (MWCN) as co-doping materials. Cyclic voltammetry was used to prepare polymerized 6-bromoindole-IL-aminographene-octadecylamine-modified, polymerized 6-bromoindole-IL-nitrogen-doped graphene, and polymerized 6-bromoindole-IL-aminographene-octadecylamine-modified-nitrogen-doped graphene-MWCN coatings on the surface of stainless steel wire. Headspace extraction combined with gas chromatography-mass spectrometry (GC-MS) was employed to construct analytical methods for detecting malathion residues in fresh vegetables or fruits, and for detecting phenolic compounds in aquatic environments. The experiment employed a single-variable method to optimize conditions such as the concentration of 6-bromoindole, the amount of ionic liquid incorporated, the octadecylamine modification of the aminated graphene, the concentration of nitrogen-doped graphene, the concentration of multi-walled carbon nanotubes, the headspace extraction time, and the headspace extraction temperature. Under optimized experimental conditions, using polymerized 6-bromoindole-IL-aminographene modified with octadecylamine-nitrogen-doped graphene-multi-walled carbon nanotubes as the extraction coating, combined with gas chromatography-mass spectrometry (GC-MS), the constructed analytical method exhibited good linear responses for phenols and malathion. The linear equation for malathion was y = 16186.99 C (μg / mL) - 1846.9, with a detection limit of 0.3-0.5 μg / mL. Among the phenols, the linear equations for 3-chloro-4-fluorophenol were y = 94020.74 C (μg / mL) + 10413, 4-chloro-3,5-dimethylphenol was y = 63399.26 C (μg / mL) - 405066.8, and 2,6-dimethoxyphenol was y = 12816.75 C (μg / mL) - The detection limit was 0.3–0.5 μg / mL. The established analytical method was used to detect malathion residues in fresh vegetables and fruits, and to analyze phenolic compounds in water samples. The recoveries of the spiked samples from pear and water samples were 99.6%–100.3% and 99.7%–100.3%, respectively, indicating that this method has good practicality.

[0056] The above descriptions are merely some embodiments of the present invention. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An extraction head for detecting phenolic compounds and malathion, characterized in that, The extraction head is a composite material of 6-Brin-Ofg-[AyttP][PF6]-MWCN.

2. The extraction head according to claim 1, characterized in that, The method for preparing the extraction head includes: A mixed solution was prepared using 6-Brin as the monomer, [AyttP][PF6] as the ionic liquid, Ofg and MWCN as co-doping materials, acetonitrile as the solvent, and tetrabutylammonium perchlorate as the electrolyte. The electrode system was inserted into the mixed solution, and a composite extraction head was prepared by cyclic voltammetry.

3. The extraction head according to claim 2, characterized in that, The concentration of 6-Brin was 0.015 mol / mL, the concentration of Ofg was 0.20 mg / mL, the concentration of MWCN was 0.20 mg / mL, and the concentration of [AyttP][PF6] was 10.0 μg / mL.

4. The extraction head according to claim 2, characterized in that, The electrode system consists of: Ag / AgCl as the reference electrode; platinum wire as the auxiliary electrode; and stainless steel wire as the working electrode.

5. A method for detecting phenolic compounds, characterized in that, Includes the following steps: The head-up extraction method described in claims 1-4 is used to extract phenolic compounds; A gas chromatography-mass spectrometry (GC-MS) model was constructed, and the extraction head was used to detect phenolic compounds.

6. The detection method according to claim 5, characterized in that, The headspace extraction of phenolic compounds using the composite extraction head includes the following steps: Prepare phenolic standard solutions; Prepare phenolic working solutions; Perform HS-SPME operation: Add saturated sodium chloride solution and phenolic standard solution to the extraction flask to form a first mixture; heat and stir the first mixture in a water bath; insert the injection device into the headspace extraction flask, and expose the extraction head of the injection device to the upper part of the extraction flask for headspace extraction. After completion, perform the GC-MS operation: After the HS-SPME operation steps are completed, Retract the extraction head into the protective sleeve, quickly insert it into the GC-MS injection port, analyze it, and then perform GC-MS separation and detection.

7. The detection method according to claim 6, characterized in that, The temperature of the thermostatic magnetic stirrer was set to 50℃, the stirring speed was 600 r / min, and the headspace extraction was performed for 30 min.

8. A method for detecting malathion, characterized in that, Includes the following steps: The head-up extraction of malathion as described in claims 1-4; A gas chromatography-mass spectrometry (GC-MS) model was constructed, and malathion was detected using the extraction head described above.

9. The detection method according to claim 8, characterized in that, The head-of-head extraction of malathion by the composite extraction head includes the following steps: Prepare a standard solution of malathion; Prepare malathion working solution; Perform HS-SPME operation: Add saturated sodium chloride solution and malathion standard solution to the extraction flask to form a first mixture; heat and stir the first mixture in a water bath; insert the injection device into the headspace extraction flask, and expose the extraction head of the injection device to the upper part of the extraction flask for headspace extraction. After completion, perform the GC-MS operation: After the HS-SPME operation steps are completed, Retract the extraction head into the protective sleeve, quickly insert it into the GC-MS injection port, analyze it, and then perform GC-MS separation and detection.

10. The detection method according to claim 9, characterized in that, The temperature of the thermostatic magnetic stirrer was set to 60℃, the stirring speed was 300 r / min, and the headspace extraction was performed for 40 min.

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