A multi-walled carbon nanotube column and a preparation method and application thereof

Abstract

This invention discloses a multi-walled carbon nanotube column, its preparation method, and its application. Carbon nanotubes of iron(III) oxide are prepared by using carboxylated carbon nanotubes. The carboxylated iron(III) oxide carbon nanotubes are then functionalized to prepare a multi-walled carbon nanotube adsorbent material synthesized by N-propylethylenediamine, Fe3O4, and N-methyl-1-octadecylamine bonds. This adsorbent material is prepared by filling an extraction tube with the multi-walled carbon nanotube adsorbent material and is used for pesticide residue detection. This method combines multi-walled carbon nanotube adsorbent material with m-PFC technology, enabling rapid and efficient detection of pesticide residues in Aster tataricus. The accuracy and precision of the detection results meet the requirements, providing a new technical means for rapid, efficient, and trace detection of pesticide residues in traditional Chinese medicinal materials, which is of great significance for ensuring the quality and safety of traditional Chinese medicinal materials.

Description

Technical Field

[0001] This invention belongs to the field of pesticide residue detection material preparation technology, specifically relating to a multi-walled carbon nanotube column, its preparation method, and its application. Background Technology

[0002] The detection of pesticide residues in traditional Chinese medicinal materials is significantly affected by interference from complex matrices. Therefore, it is crucial to purify the matrix as much as possible during pretreatment to minimize matrix effects and improve analytical accuracy. Recent pretreatment techniques include supercritical fluid extraction, ultrasound-assisted extraction, dispersion solid-phase extraction (SPE), solid-phase extraction (SPE), solid-phase microextraction (SPE), microwave-assisted solvent extraction (MAS), and liquid-phase microextraction (LC-MS), with dispersion solid-phase extraction and solid-phase extraction being the most widely used. Dispersion solid-phase extraction is represented by the QuEChERS method. Amino adsorbents, such as N-propylethylenediamine (PSA), can remove fatty acids, polar organic acids, polar pigments, and some sugars. Octadecylsilane (C18) can remove sterols, lipids, and non-polar interfering substances. Graphitized carbon black (GCB) can remove substances with aromatic structures (such as pigments), and anhydrous magnesium sulfate is used as a moisture absorbent. The QuEChERS method suffers from several drawbacks. Its relatively fixed formulation makes it unsuitable for detecting pesticide residues in various Chinese medicinal herbs. Furthermore, adsorbents like GCB exhibit specific adsorption for pesticides with planar structures containing benzene rings (such as fipronil, carbendazim, and chlorpyrifos), leading to low recovery rates. Additionally, it suffers from high consumption of purification materials and solvents, low adsorption efficiency, and cumbersome operation. Solid-phase extraction (SPE) primarily utilizes different SPE columns, such as purification tubes for QuEChERS components, hydrophilic-lipophilic balanced material (HLB SPE) SPE columns, and graphitized carbon black amino composite SPE columns. However, these methods also suffer from low adsorption efficiency, limited applicability, and cumbersome operation.

[0003] Multi-walled carbon nanotubes (MWCNTs) are hollow tubular materials composed of multiple layers of graphene sheets. They possess advantages such as large specific surface area, strong adsorption capacity, abundant x-electrons, and chemical stability. They have attracted considerable attention due to their excellent adsorption capacity for hydrophobic organic compounds, extremely high surface area-to-volume ratio, good chemical stability, and ease of functionalization. MWCNTs have been successfully applied as adsorbents for both nonpolar and polar organic compounds, interacting with aromatic compounds of these compounds through π-π interactions. Studies have found that MWCNTs, as r-DSPE adsorbents, exhibit superior scavenging performance compared to PSA and GCB used in the QuEChERS method. However, MWCNTs suffer from poor water compatibility and insufficient wettability, resulting in limited applicability to aqueous solutions of traditional Chinese medicine matrices. Research has shown that in determining pesticide residues in pigment-rich tomatoes, the recovery rates, from highest to lowest, are: MWCNTs-OH > MWCNTs-COOH > MWCNTs-NH2 > GCB. By connecting different functional groups, the water wettability of MWCNTs is improved to a certain extent, making them an excellent alternative to GCB. However, their adsorption performance for fatty acids, organic acids, and non-polar and low-polarity interfering substances is still insufficient.

[0004] Therefore, it is essential to develop a new adsorption material to improve detection sensitivity and lower the detection limit. Summary of the Invention

[0005] To address at least one of the aforementioned problems, this invention provides a multi-walled carbon nanotube column, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention employs the following technical means: The first aspect of the present invention provides a method for preparing a multi-walled carbon nanotube column, wherein the multi-walled carbon nanotube column is prepared by filling an extraction tube with a multi-walled carbon nanotube adsorbent material; the preparation of the multi-walled carbon nanotube adsorbent material includes the following steps: S1. Preparation of carbon nanotubes (Fe3O4): Ferric chloride, anhydrous sodium acetate, and carboxylated carbon nanotubes are added to ethylene glycol and ultrasonically mixed until homogeneous. The mixture is then transferred to a polytetrafluoroethylene (PTFE) liner and placed in a high-temperature reactor for reaction. After the reaction, the mixture is washed sequentially with ultrapure water and anhydrous ethanol, and then dried. More specifically, the mixture is reacted at 150-250℃ for 6-8 hours in a high-temperature reactor. After the reaction, the mixture is washed sequentially with ultrapure water 4-5 times and anhydrous ethanol 2-3 times, and then dried. S2, Functionalization of Carboxylated Carbon Nanotubes with Iron Oxide: The carbon nanotubes with iron oxide obtained in S1, toluene, PSA, N-methyl-1-octadecylamine, and condensing agent are added sequentially to the reaction vessel. After ultrasonic mixing, the mixture is heated in an oil bath and stirred under reflux for 20-24 hours. After the reaction is completed, the mixture is filtered, washed 5-8 times with anhydrous ethanol, and dried.

[0007] In some embodiments of the present invention, in step S1, the ratio of ethylene glycol, ferric chloride, anhydrous sodium acetate, and carboxylated carbon nanotubes is (100-150) mL: 5g: 15g: 1g.

[0008] In some embodiments of the present invention, in step S2, the ratio of toluene, carbon nanotube iron oxide, PSA, N-methyl-1-octadecylamine, and condensing agent is (15-20) mL:1g:4g:2g:2g.

[0009] In some embodiments of the present invention, the condensing agent is dicyclohexylcarbodiimide.

[0010] In some embodiments of the present invention, the extraction tube is filled with a mixture of magnesium sulfate and multi-walled carbon nanotube adsorbent.

[0011] In some embodiments of the present invention, in the mixture of multi-walled carbon nanotube adsorbent and magnesium sulfate, the mass ratio of magnesium sulfate to multi-walled carbon nanotube adsorbent is (5-30):1. Preferably, the mass ratio of magnesium sulfate to multi-walled carbon nanotube adsorbent is 15:1.

[0012] The second aspect of the present invention provides the application of multi-walled carbon nanotube columns prepared by the method described in the first aspect in the detection of pesticide residues in crops.

[0013] In some embodiments of the present invention, the pesticide includes mefenoxam-O, ethoprophos, amitraz, phosmet, phorate, α-HCH, terbufos, β-HCH, phorate, γ-HCH, flufenoxuron, δ-HCH, aldrin, methyl parathion, 2,4'-trichlorfon, fipronil sulfoxide, fipronil, fipronil, trichlorfon, methyl isofenphos, methamidophos, α-endosulfan, fipronil sulfone, DDE-P,P', fenprophos, methyl thion. DDT-O,P', β-endosulfan, DDD-P,P', DDT-P,P', parathion, methamidophos, aldicarb sulfoxide, phosmet, aldicarb sulfone, amitraz, 3-hydroxycarbofuran, thiocyclam, benzylphosphonate sulfoxide, phosphamidon, aldicarb, mesosulfuron, carbofuran, chlorsulfuron, phorate sulfoxide, methamidophos, phorate sulfone, terbufos sulfoxide, methamidophos, benzylphosphonate, terbufos sulfone, chlorpyrifos, thiophosphonate, methyl isofenphos, phosmet, phorate.

[0014] In some embodiments of the present invention, the detection methods include gas chromatography-tandem mass spectrometry and liquid chromatography-tandem mass spectrometry.

[0015] Beneficial effects of the present invention Compared with the prior art, the present invention has the following beneficial effects: (1) Fe3O4@MWCNTs-COOH@PSA@C18 material is a MWCNTs material. Because it bonds MWCNTs-COOH, PSA and C18 with different matrix adsorption characteristics together, it forms a pretreatment suitable for the detection of pesticide residues in Chinese medicinal materials with complex matrix characteristics. At the same time, because it is bonded with magnetic Fe3O4, it can also be separated by the r-DSPE method of magnetic adsorption. It realizes multiple adsorption characteristics of one material and two separation methods, which greatly facilitates the selection of pretreatment methods.

[0016] (2) An improved m-PFC method for pesticide residue detection. Like QuEChERS, m-PFC is a pretreatment technique for dispersion solid phase extraction. However, m-PFC has advantages such as being faster, more convenient, more efficient, and more environmentally friendly. It is also easier to achieve uniform and automated pretreatment, which can improve the stability of detection. The matrix can be removed by pushing and pulling 2-3 times, which takes about 20 seconds. It is faster and more convenient than QuEChERS. At the same time, because the sample volume is about 2-3 ml, the amount of reagents and materials used is small, which is also more environmentally friendly. Attached Figure Description

[0017] Figure 1 The XRD pattern of the material in Embodiment 1 of the present invention is shown; Figure 2 The XPS spectrum of the material in Example 1 of the present invention is shown; Figure 3 The SEM images of the material in Example 1 of this invention are shown; Figure 4 The VSM spectrum of the material in Embodiment 1 of the present invention is shown; Figure 5 The TIC chromatograms of the blank sample solution and standard solution of aster under GC-MS / MS detection method in Example 3 of the present invention are shown. Figure 6 The TIC chromatograms of the blank sample solution and standard solution of aster under LC-MS / MS detection method in Example 3 of the present invention are shown. Detailed Implementation

[0018] The following examples are used to illustrate preferred embodiments of the invention. Those skilled in the art will understand that the techniques disclosed in the examples represent techniques discovered by the inventors that can be used to implement the invention, and therefore can be considered preferred embodiments for implementing the invention. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed herein, still yielding the same or similar results, without departing from the spirit or scope of the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials disclosed herein and cited therein are incorporated herein by reference. Many equivalent techniques of specific embodiments of the invention described herein will be recognized or can be understood by ordinary experimentation by those skilled in the art. These equivalents will be included in the claims.

[0020] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0021] Example 1: Synthesis of Multi-walled Carbon Nanotubes: Fe3O4@MWCNTs-COOH@PSA@C18 1. Preparation of carboxylated carbon nanotubes with iron oxide Preparation of carbon nanotubes (Fe3O4): 60 ml of ethylene glycol, 2 g of ferric chloride, 6 g of anhydrous sodium acetate, and 0.4 g of carboxylated carbon nanotubes were added sequentially to a 100 ml beaker. The mixture was ultrasonically mixed until homogeneous, then transferred to a 100 ml polytetrafluoroethylene (PTFE) liner. The mixture was then placed in a high-temperature reactor and reacted at 200 °C for 8 hours. After the reaction, the mixture was washed five times with ultrapure water and three times with anhydrous ethanol, and then dried in an oven at 80 °C.

[0022] 2. Functionalization of carboxylated carbon nanotubes with iron oxide 5g of acidified iron(III) oxide carbon nanotubes, 100ml of toluene, 20g of PSA, 10g of N-methyl-1-octadecylamine, and 10g of the condensing agent dicyclohexylcarbodiimide (DCC) were sequentially added to a 250ml three-necked flask. After ultrasonic mixing, the mixture was heated in an oil bath at 120℃ with stirring at 250rpm and refluxed for 24h. After the reaction was completed, the mixture was filtered and washed 5-8 times with anhydrous ethanol. Then, it was dried in an oven at 70℃ to obtain the multi-walled carbon nanotube material: Fe3O4@MWCNTs-COOH@PSA@C18.

[0023] Structural characterization: XRD patterns as shown Figure 1 As shown, the XPS plot is as follows Figure 2 As shown, the SEM image is as follows Figure 3 As shown, the VSM map is as follows: Figure 4 As shown.

[0024] The XRD pattern shows that PSA, Fe3O4, and N-methyl-1-octadecylamine are bonded to MWCNTs; the XPS pattern further characterizes the composition of Fe3O4@MWCNTs-COOH@PSA@C18; the SEM image clearly shows that Fe3O4 nanospheres and MWCNTs are intertwined; the VSM pattern shows that the saturation magnetization of the new material is about 40 emu / g.

[0025] The spectral results from VSM, SEM, XPS, and XRD confirm that Fe3O4@MWCNTs-COOH@PSA@C18 has been successfully synthesized.

[0026] Example 2: Preparation of Multi-walled Carbon Nanotube Columns The multi-walled carbon nanotube column is an m-FPC column prepared by filling an extraction tube with multi-walled carbon nanotube material and magnesium sulfate powder: take an m-FPC syringe as the extraction tube, fill the syringe with the multi-walled carbon nanotube material and magnesium sulfate white powder prepared in Example 1, and the multi-walled carbon nanotube column is obtained.

[0027] Example 3: Application of Multi-walled Carbon Nanotube Columns in Pesticide Residue Detection A rapid filtration purification (m-PFC) column was prepared using Fe3O4@MWCNTs-COOH@PSA@C18 prepared in Example 1 as the packing material. The method of determining prohibited pesticide residues in medicinal materials and processed medicinal slices (plants) in General Chapter 2341 of the 2020 edition of the Chinese Pharmacopoeia was adopted. Aster tataricus was used as a sample to detect and analyze pesticide residues in it to evaluate the feasibility of the packing material.

[0028] (1) Preparation of mixed standard solutions Take the following pesticide mixture reference solutions that meet the qualification requirements, and dilute them with acetonitrile to an appropriate multiple based on the pesticide residue situation in the Chinese medicinal materials.

[0029] Table 1. Types of banned pesticides

[0030] (2) Preparation of internal standard solution Accurately measure an appropriate amount of triphenyl phosphate standard solution and add acetonitrile to prepare a solution with a concentration of 0.1 mg / L, which will be used as an internal standard solution.

[0031] (3) Sample preparation Take an appropriate amount of Aster tataricus sample, grind it into powder and mix it evenly. Accurately weigh 5.0 g, place it in an extraction vessel, add 1 g NaCl, then add the corresponding volume of standard solution, shake to disperse, and place it in an automatic homogenizer for extraction (50 mL acetonitrile). Centrifuge and collect the supernatant. Add 1 g NaCl to each sample and place it in a homogenizer for a second extraction. Centrifuge and combine the supernatants.

[0032] The supernatant obtained from the two extractions was concentrated to 3-5 mL under reduced pressure at 40℃ and 100 Pa in a parallel vacuum concentrator. The solution was taken out, and the volume was adjusted to 10 mL. The solution was mixed well, and the two groups of solutions were purified by passing them through a new material column. The purified solution was filtered through a microporous membrane and then placed into a sample vial as the test solution.

[0033] (4) Detection of pesticide residues by gas chromatography-tandem mass spectrometry (GC-MS / MS) Chromatographic column: an elastic quartz capillary column with (50% phenyl)-methylpolysiloxane as the stationary phase.

[0034] Table 2 Temperature gradients in GC-MS / MS

[0035] Detection was performed using a triple quadrupole tandem mass spectrometer. The ion source was an electron impact source at 250°C, and the collision gas was nitrogen / argon. The mass spectrometer transmission interface temperature was 250°C. The mass spectrometry monitoring mode was multiple reaction monitoring.

[0036] Table 3. Ion-pair ion mass monitoring by GC-MS / MS

[0037] Sample preparation for GC-MS / MS detection: Take 1 mL of the extracted sample solution, and repeat for 6 portions. Blow nitrogen to approximately 0.6 mL. Then add 10 μL, 20 μL, 50 μL, 100 μL, 150 μL, and 200 μL of the mixed standard solution, respectively. Dilute with acetonitrile to 1 mL and mix well. Add 0.3 mL of internal standard triphenyl phosphate to the GC-MS system. After the solution stabilizes, filter through a microporous membrane. Take 1 mL of the filtered solution into a vial as the test solution.

[0038] The test solution was injected and detected on a GC-MS / MS instrument. The detection results were used to establish a linear regression equation with peak area as the ordinate and concentration as the abscissa. The standard curve for the detection of pesticide residues in Aster tataricus by GC-MS / MS is shown in Table 4.

[0039] Table 4. Standard curves for GC-MS / MS detection of pesticide residues in Aster tataricus

[0040] In General Chapter 9101 of the 2020 edition of the Chinese Pharmacopoeia, the linearity test requires that the standard curve R² ≥ 0.99. As can be seen from the results in the table above, the R² of each compound meets the standard within the design range, indicating a good linear relationship.

[0041] Weigh 18 samples, each 5.0 g, and divide them into three groups: low, medium, and high concentration. Add 1.0 g NaCl to each group. Add 0.5 mL of standard solution to the low concentration group, 1.0 mL of standard solution to the medium concentration group, and 1.5 mL of standard solution to the high concentration group. Place the samples in an automated homogenizer for homogenization. After homogenization, centrifuge and collect the supernatant. Add 1.0 g NaCl to the precipitate and homogenize again. Centrifuge again and collect the supernatant. Combine the two supernatants, concentrate under reduced pressure to 3-5 mL, and make up to 10 mL with acetonitrile.

[0042] After purification using the new material column, 1.0 mL of sample solution was taken and 0.3 mL of internal standard triphenyl phosphate was added to the gas chromatography-mass spectrometry (GC-MS) sample. After the solution stabilized, it was filtered through a microporous membrane and placed into a vial as the test solution. The accuracy statistics for pesticide determination are shown in Table 5.

[0043] Table 5. Accuracy statistics of GC-MS / MS detection of pesticide residues in Aster tataricus.

[0044] In General Chapter 9101 of the 2020 edition of the Chinese Pharmacopoeia, the accuracy test requires that the RSD of each group of detected components be ≤8%. Simultaneously, the 2020 edition of the Chinese Pharmacopoeia requires that the recovery rate for pesticide residue detection be between 60% and 120%. As shown in the table above, the recovery rates and RSDs of each substance at low, medium, and high concentrations all meet the standards.

[0045] After purification, 1.0 mL of sample was taken and purged with nitrogen to approximately 0.6 mL. Five aliquots were then diluted with 10 μL, 20 μL, 30 μL, 40 μL, and 50 μL of standard solution, respectively, and brought to a final volume of 1 mL with acetonitrile. 0.3 mL of triphenyl phosphate was added, and after the solution stabilized, it was filtered through a microporous membrane and transferred to a vial as the test solution. The limits of detection and quantitation were determined, and the results are shown in Table 6 below.

[0046] Table 6. Statistics of detection limits and quantitation limits for pesticide residues in Aster tataricus by GC-MS / MS.

[0047] The low-concentration group samples from the accuracy test experiment were taken and injected again at intervals of 6h, 12h, and 24h after the first injection. The RSD of each group of data was calculated, and the results are shown in Table 7 below.

[0048] Table 7. Stability statistics of pesticide residues in Aster tataricus detected by GC-MS / MS.

[0049] Comparison of TIC spectra of standard and aster blank matrix as follows Figure 5 As shown.

[0050] The results showed that the blank sample solution of Aster tataricus did not contain any substances that could interfere with the detection results of various pesticide components in the standard solution, and met the specificity standard.

[0051] (5) Liquid chromatography-tandem mass spectrometry (LC-MS / MS) Chromatographic column: The column is packed with octadecylsilane-bonded silica gel.

[0052] Using 0.1% formic acid solution (containing 5 mmol / L ammonium formate) as mobile phase A, and acetonitrile-0.1% formic acid solution (containing 5 mmol / L ammonium formate) (95:5) as mobile phase B, elute according to the gradient in the table below; the flow rate is 0.3 mL / min, and the column temperature is 40 °C.

[0053] Table 8. LC-MS / MS mobile phase gradient

[0054] Detection was performed using a triple quadrupole tandem mass spectrometer; the ion source was an electrospray ionization source in positive ion scanning mode. Multiple reaction monitoring (MRM) was used for monitoring.

[0055] Table 9. Ion-pair ion mass monitoring by LC-MS / MS

[0056] The sample processing is the same as that for GC-MS / MS, except that water is added when preparing the test solution after purification.

[0057] The results of LC-MS / MS detection are as follows: Table 10 Standard curves for LC-MS / MS detection of pesticide residues in Aster tataricus

[0058] Table 11. Accuracy Statistics of LC-MS / MS Detection of Pesticide Residues in Aster tataricus

[0059] Table 12. Statistics of detection limits and quantitation limits for pesticide residues in Aster tataricus by LC-MS / MS.

[0060] Table 13. Stability statistics of pesticide residues in Aster tataricus detected by LC-MS / MS.

[0061] Comparison of TIC spectra of standard and aster blank matrix as follows Figure 6 As shown.

[0062] The results showed that the blank sample solution of Aster tataricus did not contain any substances that could interfere with the detection results of various pesticide components in the standard solution, and met the specificity standard.

[0063] To investigate the treatment effect of the new material prepared in this application compared with commonly used existing purification materials, we also compared the pesticide residue recovery rate of commercially available Agilent brand HLB columns (HLB-A), commercially available Shimadzu brand HLB columns (HLB-B), commercially available Waters brand HLB columns (HLB-C), and purification columns assembled with different masses of the material in this application. The purification column schemes assembled with different masses of the material in this application are shown in Table 14.

[0064] Table 14 Purification columns assembled with different masses from the materials in this application

[0065] The results of GC-MS / MS analysis are shown in Tables 15-16. Specifically, Scheme 1-1 uses the purification column prepared with the material from Scheme 1, with three parallel experiments and the average recovery rate after one extraction; Scheme 1-2 uses the purification column prepared with the material from Scheme 1, with three parallel experiments and the average recovery rate after two extractions; Scheme 1-3 uses the purification column prepared with the material from Scheme 1, with three parallel experiments and the average recovery rate after three extractions; the subsequent Schemes 2-4 have the same numbering meaning, differing only in that the materials used to prepare the purification columns are the corresponding schemes listed in Table 14.

[0066] Table 15 Results of pesticide residue recovery rates for multi-walled carbon nanotube materials with different filling schemes.

[0067] The values ​​in Table 16 are the average results of three extraction and purification cycles using the corresponding materials in the purification column.

[0068] Table 16 Results of pesticide residue recovery rates for different schemes and commercially available materials in this application.

[0069] The results of LC-MS / MS analysis are shown in Tables 17-18. Scheme 1-1 uses the purification column prepared with the material from Scheme 1, and three parallel experiments were conducted, with the average recovery rate after one extraction for each scheme. Scheme 1-2 uses the purification column prepared with the material from Scheme 1, and three parallel experiments were conducted, with the average recovery rate after two extractions for each scheme. Scheme 1-3 uses the purification column prepared with the material from Scheme 1, and three parallel experiments were conducted, with the average recovery rate after three extractions for each scheme. The subsequent schemes 2-4 have the same numbering meaning; the only difference is that the purification column is prepared using the corresponding material from Table 14.

[0070] Table 17 Results of pesticide residue recovery rates for different filling schemes of multi-walled carbon nanotube materials.

[0071] The values ​​in Table 18 are the average results of three extraction and purification cycles using the corresponding materials in the purification column.

[0072] Table 18 Results of pesticide residue recovery rates for different schemes and commercially available materials in this application.

[0073] The results showed that, regardless of whether LC-MS / MS or GC-MS / MS was used for detection, the pesticide recovery rate after purification using the material of this application was higher than that of other commercially available materials. The purification material in this application, when used in combination with magnesium sulfate, has a good and stable purification effect. The multi-walled carbon nanotube material can greatly avoid the adverse effects on the detection results caused by the large weight difference between multiple materials and the difficulty in controlling the uniformity of the filler when multiple materials are packed.

[0074] We prepared a purification column using the multi-walled carbon nanotube (MWCNT) material prepared in Example 1, along with magnesium sulfate, for pesticide residue detection. The results showed that the modified MWCNTs performed well in pesticide residue detection, effectively removing impurities and interfering substances from the sample. It exhibited good performance in terms of specificity, accuracy, precision, and stability. The combination of modified MWCNTs and m-PFC technology enables rapid and efficient detection of pesticide residues in Aster tataricus. This method not only rapidly extracts the effective components from Aster tataricus samples but also achieves the required accuracy and precision. It provides a new technical means for the rapid, efficient, and trace detection of pesticide residues in traditional Chinese medicinal materials, which is of great significance for ensuring the quality and safety of these materials.

[0075] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. A method for preparing multi-walled carbon nanotube columns, characterized in that, The multi-walled carbon nanotube column was prepared by filling an extraction tube with a mixture of magnesium sulfate and multi-walled carbon nanotube adsorbent material; the preparation of the multi-walled carbon nanotube adsorbent material includes the following steps. S1. Preparation of carbon nanotubes (Fe3O4): Ferric chloride, anhydrous sodium acetate, and carboxylated carbon nanotubes were added to ethylene glycol and ultrasonically mixed until homogeneous. The mixture was then transferred to a polytetrafluoroethylene liner and placed in a high-temperature reactor for reaction. After the reaction, the mixture was washed sequentially with ultrapure water and anhydrous ethanol and dried. The ratio of ethylene glycol, ferric chloride, anhydrous sodium acetate, and carboxylated carbon nanotubes was (100-150) mL: 5 g: 15 g: 1 g. S2, Functionalization of Carboxylated Carbon Nanotubes with Iron Oxide: The carbon nanotubes with iron oxide obtained in S1, toluene, N-propylethylenediamine, N-methyl-1-octadecylamine, and condensing agent were added sequentially to the reaction vessel. After ultrasonic mixing, the mixture was heated in an oil bath and stirred under reflux for 20-24 hours. After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol, and dried. The ratio of toluene, carbon nanotubes with iron oxide, N-propylethylenediamine, N-methyl-1-octadecylamine, and condensing agent was (15-20) mL: 1 g: 4 g: 2 g: 2 g.

2. The method for preparing a multi-walled carbon nanotube column according to claim 1, characterized in that, The condensing agent is dicyclohexylcarbodiimide.

3. The method for preparing a multi-walled carbon nanotube column according to claim 1, characterized in that, The reaction is carried out in a high-temperature reactor at a temperature of 150-250℃ for 6-8 hours.

4. The method for preparing a multi-walled carbon nanotube column according to claim 1, characterized in that, The mass ratio of magnesium sulfate to multi-walled carbon nanotube adsorbent is (5-30):

1.

5. The application of multi-walled carbon nanotube columns prepared by the method according to any one of claims 1-4 in the detection of pesticide residues in crops.

6. The application according to claim 5, characterized in that: The pesticides mentioned include phosmet, methamidophos, phorate, α-HCH, terbufos, β-HCH, monocrotophos, γ-HCH, flufenoxuron, δ-HCH, aldrin, methyl parathion, fipronil sulfoxide, fipronil, trichlorfon, methamidophos, α-endosulfan, fipronil sulfone, p,p'-DDE, fenpropathrin, methyl thion, o,p'-DDT, and β-endosulfan. p,p'-DDD, p,p'-DDT, parathion, methamidophos, aldicarb sulfoxide, aldicarb sulfone, amitraz, 3-hydroxycarbofuran, thiocyclophosphamide, benzylphosphonate sulfoxide, phosphamidon, aldicarb, mesosulfuron-methyl, carbofuran, chlorsulfuron-methyl, phorate sulfoxide, benzylphosphonate, demeton-methyl, phorate sulfone, terbufos sulfoxide, terbufos sulfone, chlorpyrifos, thiophosphonate, methyl isofenphos, phosmet.

7. The application according to claim 6, characterized in that: The detection methods include gas chromatography-tandem mass spectrometry and liquid chromatography-tandem mass spectrometry.

Images