Preparation method of MOFs modified melamine foam and its application in solid-phase extraction of organophosphorus pesticides by gun head

Abstract

The present invention discloses a preparation method of melamine foam MF modified by metal organic frameworks (MOFs) and its application in the solid phase extraction of organophosphorus pesticides in fruits and vegetables using a gun tip. The method comprises the following steps: (1) pretreating the foam; (2) synthesizing two MOFs materials, Ti-MIL-125 and Fe-MIL-101, respectively; (3) uniformly fixing the MOFs on the foam under the action of a crosslinking agent, polyvinylidene fluoride (PVDF), to complete the preparation of MOFs-modified foam, i.e., MF / PVDF / MOFs; and (4) filling the MF / PVDF / MOFs into a 1 mL gun tip, and realizing rapid extraction of organophosphorus pesticides in fruits and vegetables using a gun tip solid phase extraction method.

Description

Technical Field

[0001] The present invention relates to the technical field of organophosphorus pesticide analysis and detection, and in particular to a method for preparing metal organic framework (MOFs) modified melamine foam (MF) and a method for rapidly extracting organophosphorus pesticides using a tip-solid phase extraction (PT-SPE) method. Background Art

[0002] Organophosphorus pesticides generally refer to compounds containing CP, COP, CSP, or CNP groups. Due to their high efficiency and broad spectrum, they are widely used as insecticides, fungicides, or herbicides in a variety of fields, including fruits, vegetables, oils, and grains. However, due to the incorrect and excessive use of organophosphorus pesticides, they have caused serious pollution. In 2005, the total pesticide production reported exceeded 1×10 6 Tons per year, and organophosphorus pesticide use accounts for approximately 50% of all pesticides. In 2021, the total concentration of organophosphorus pesticide residues in Chinese farmland ranged from 9.93 to 303 ng / g. From farm to table, organophosphorus pesticides can accumulate through the food chain, damaging the nervous system and causing cholinesterase disorders and other diseases. Therefore, monitoring organophosphorus pesticide contamination is of great significance, and rapid pretreatment of various samples is key to improving detection efficiency.

[0003] Because most organophosphorus pesticides are present at low levels in food and the environment, direct detection is difficult and can result in significant matrix effects, which can interfere with test results. Therefore, sample pretreatment is an essential step before detecting organophosphorus pesticides. Currently, the main pretreatment methods for pesticide residues include liquid phase extraction, solid phase extraction, magnetic solid phase extraction, and QuEChERS. Liquid-liquid extraction generally partitions and separates pesticide residues based on their different solubility in the solution. This method is simple, easy to operate, highly adaptable, and compatible with most detection instruments, but it consumes a lot of organic reagents. Magnetic solid phase extraction typically involves modifying a magnetic material with other compounds to form a composite material for enrichment of target compounds in solution. Using a magnet, magnetic adsorbents dispersed in the solution can be rapidly aggregated and collected, effectively avoiding centrifugation and simplifying the extraction process. However, this can result in material loss during collection. Compared to these methods, PT-SPE offers advantages such as portability, ease of control, and the lack of material recovery. Various methods exist for preparing pipette tip extractions. Adsorbents can be synthesized directly within the pipette tip, but the control of the synthesized materials is difficult. Typically, adsorption materials can be prepared in advance, often in powder form, for easy loading into the gun tip. However, this can lead to material leakage, high backpressure, and extraction difficulties. To address these issues, porous materials such as MF can be considered, enhanced with other adsorbent materials. As a monolithic material, this can be directly loaded into the gun tip to extract the target.

[0004] The extraction of organophosphorus pesticides depends crucially on the choice of adsorbent. MOFs are crystalline materials formed by the self-assembly of metal ions or metal oxide clusters with organic ligands. Due to their large surface area and porous structure, MOFs exhibit excellent adsorption properties for most organophosphorus pesticides. Different MOFs can be selected based on the properties of the target compound and the extraction conditions. Furthermore, the synergistic effect of multiple MOFs can effectively improve the pore structure, leveraging their strengths and compensating for their weaknesses, thereby enabling the simultaneous extraction of multiple targets. Summary of the Invention

[0005] In view of the problems of the prior art, the purpose of the present invention is to provide a method for preparing MOFs modified melamine foam and the application of the same in the solid phase extraction of organophosphorus pesticides using a gun tip.

[0006] To achieve the above object, the present invention adopts the following technical solution: A method for preparing a MOFs-modified melamine foam of the present invention comprises the following steps:

[0007] (1) MF pretreatment: MF was cut into cubes of 1 × 1 × 1 cm, ultrasonically cleaned with ethanol, dried, and set aside;

[0008] (2) Synthesis of Ti-MIL-125 and Fe-MIL-101: Terephthalic acid and tetrabutyl titanate were dissolved in N,N-dimethylformamide and methanol, with the molar ratio of terephthalic acid to tetrabutyl titanate being 3:2 and the volume ratio of N,N-dimethylformamide to methanol being 9:1; the mixture was then transferred to a high-temperature and high-pressure reactor and heated at 150°C to obtain Ti-MIL-125; terephthalic acid and FeCl3·6H2O were dissolved in N,N-dimethylformamide at a molar ratio of 1:2, with the concentration of terephthalic acid being 0.075 mol / L and the concentration of FeCl3·6H2O being 0.15 mol / L, and heated at 110°C for 24 h to obtain Fe-MIL-101; Ti-MIL-125 and Fe-MIL-101 were washed three times with N,N-dimethylformamide and methanol and dried;

[0009] (3) Preparation of PVDF / MOFs slurry: PVDF was dissolved in N,N-dimethylformamide at a concentration of 40 mg / mL, Ti-MIL-125 and Fe-MIL-101 were dispersed in N,N-dimethylformamide at a mass ratio of 1:2, and the total concentration of Ti-MIL-125 and Fe-MIL-101 was 40 mg / mL. The two were then mixed and stirred at room temperature for 30-60 min.

[0010] (4) Preparation of MF / PVDF / MOFs: The above slurry was added dropwise to each small MF cube, and squeezed repeatedly to make the slurry evenly distributed on the MF. The slurry was then dried at a temperature of 60-100 °C for 8-16 h to completely fix the MOFs on the MF, thereby obtaining MOFs-modified MF, i.e., MF / PVDF / MOFs.

[0011] Furthermore, in step (2), Ti-MIL-125 and Fe-MIL-101 were synthesized: 0.996 g of terephthalic acid and 1.36 g of tetrabutyl titanate were dissolved in 36 mL of N,N-dimethylformamide and 4 mL of methanol, and then the mixture was transferred to a high-temperature and high-pressure reactor and heated at 150°C for 24 h to obtain Ti-MIL-125; 0.498 g of terephthalic acid and 1.62 g of FeCl3·6H2O were dissolved in 40 mL of N,N-dimethylformamide and heated at 110°C for 24 h to obtain Fe-MIL-101; Ti-MIL-125 and Fe-MIL-101 were washed three times with N,N-dimethylformamide and methanol and dried.

[0012] Furthermore, in step (3), PVDF / MOFs slurry was prepared: PVDF was fully dissolved in N,N-dimethylformamide with a solubility of 40 mg / mL; Ti-MIL-125 and Fe-MIL-101 were dispersed in N,N-dimethylformamide at a mass ratio of 1:2 with a total concentration of 40 mg / mL, and then the two were mixed and stirred at room temperature for 30 min.

[0013] Furthermore, in step (4), MF / PVDF / MOFs were prepared by taking 0.4 mL of the above slurry and dropping it onto each MF cube, repeatedly squeezing it to make the slurry evenly distributed on the MF, and drying it at 80 °C for 12 h to completely fix the MOFs on the MF to prepare MF / PVDF / MOFs.

[0014] The invention discloses an application of the MOFs-modified melamine foam in the rapid extraction and enrichment of organophosphorus pesticides.

[0015] Beneficial effects: In the present invention, MOFs are uniformly modified on MF materials as adsorbents under the action of cross-linking agent polyvinylidene fluoride (PVDF). The established PT-SPE method helps to achieve rapid extraction of organophosphorus pesticides in some complex matrices.

[0016] Compared with the existing technology, the present invention has the following advantages: (1) The present invention uses MF as the base material, and uniformly coats two MOFs materials, Ti-MIL-125 and Fe-MIL-101, on MF through the cross-linking effect of PVDF to obtain MF / PVDF / MOFs, which is directly filled into a 1 mL pipette tip, which can achieve rapid extraction of various organophosphorus pesticides (<3 min) and has been successfully applied to the rapid extraction of organophosphorus pesticides in fruits and vegetables.

[0017] (2) The PT-SPE method established by the present invention using MF / PVDF / MOFs simplifies the sample pretreatment process and improves the extraction efficiency. The synergistic effect of Ti-MIL-125 and Fe-MIL-101 enriches the pore structure and improves the extraction capacity of various organophosphorus pesticides. Therefore, the PT-SPE method based on MF / PVDF / MOFs can achieve good application of organophosphorus pesticides in food samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the process for preparing MF / PVDF / MOFs and PT-SPE of the present invention;

[0019] Figure 2 The physical pictures of MF and MF / PVDF / MOFs prepared in the present invention;

[0020] Figure 3 is the SEM image of MF / PVDF / MOFs of the present invention;

[0021] Figure 4 FT-IR graph of MF / PVDF / MOFs of the present invention;

[0022] Figure 5 is the XRD pattern of MF / PVDF / MOFs of the present invention;

[0023] Figure 6 This is a comparison chart of the effects of the modified materials of the present invention on the recovery rate;

[0024] Figure 7 This is a comparison chart of the effects of the addition ratio and concentration of MOFs on the recovery rate of the present invention;

[0025] Figure 8 This is a comparison chart of the effect of the filling quality of the MF / PVDF / MOFs tip on the recovery rate of the present invention;

[0026] Figure 9 This is a comparison diagram of the effects of different salt concentrations on recovery rates of the present invention;

[0027] Figure 10 This is a comparison diagram of the effects of different pH values on recovery rates in the present invention;

[0028] Figure 11 This is a comparison chart showing the effects of different extraction and elution cycle times on recovery rates in the present invention;

[0029] Figure 12 This is a comparison chart of the effects of different elution solvents and volumes on the recovery rate of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described in detail by the following test examples, but it should be noted that the scope of the present invention is not limited by these test examples.

[0031] Example 1

[0032] The present invention provides a method for preparing MF based on MOFs modification, comprising the following steps:

[0033] (1) MF pretreatment: Cut the MF into cubes of 1 × 1 × 1 cm, clean them with ethanol ultrasonically, dry them, and set aside.

[0034] (2) Synthesis of Ti-MIL-125 and Fe-MIL-101: 0.996 g of terephthalic acid and 1.36 g of tetrabutyl titanate were dissolved in 36 mL of N,N-dimethylformamide and 4 mL of methanol. The mixture was then transferred to a high-temperature and high-pressure reactor and heated at 150 °C for 24 h to obtain Ti-MIL-125. 0.498 g of terephthalic acid and 1.62 g of FeCl3·6H2O were dissolved in 40 mL of N,N-dimethylformamide and heated at 110 °C for 24 h to obtain Fe-MIL-101. Ti-MIL-125 and Fe-MIL-101 were washed three times with N,N-dimethylformamide and methanol and dried in vacuo at 60 °C.

[0035] (3) Preparation of PVDF / MOFs slurry: 400 mg of PVDF was fully dissolved in 10 mL of N,N-dimethylformamide, Ti-MIL-125 and Fe-MIL-101 were dispersed in 10 mL of N,N-dimethylformamide at a mass ratio of 1:2, with a concentration of 40 mg / mL, and then the two were mixed and stirred at room temperature for 30 min;

[0036] (4) Preparation of MF / PVDF / MOFs: 0.4 mL of the above slurry was added dropwise to each MF cube, and the slurry was squeezed repeatedly to make the slurry evenly distributed on the MF. The slurry was then dried at 80 °C for 12 h to completely fix the MOFs on the MF, thereby obtaining MOFs-modified MF, i.e., MF / PVDF / MOFs.

[0037] The invention relates to the application of the MOFs-modified MF in the rapid extraction and enrichment of organophosphorus pesticides.

[0038] The present invention provides a PT-SPE rapid extraction method and GC-FTD analysis method for organophosphorus pesticides, comprising the following steps: filling the tip of a gun with MF / PVDF / MOFs to achieve rapid extraction and enrichment of organophosphorus pesticides in fruits and vegetables:

[0039] (1) Extraction step: Connect the gun head of the filling material and the syringe through a rubber tube, and achieve the extraction process of the organophosphorus pesticide by repeated suction times; the extraction is completed within 2 minutes; and the elution is completed within 1 minute.

[0040] (2) Elution step: Connect the tip directly to the pipette, repeat the aspiration times, and elute with methanol;

[0041] (3) Analysis: The eluate was filtered through a 0.22 μm organic filter membrane and analyzed by GC-FTD detector. The analysis of organophosphorus pesticides was performed using a GC-2030 chromatograph equipped with an FTD detector (Shimadzu, Japan) and an HP-5 commercial capillary column (30 m × 0.32 mm × 0.25 μm). The detector inlet temperature was 250 °C, the injection volume was 1 μL; the carrier gas was nitrogen (99.999%). The column temperature program was set as follows: initial temperature of 100 °C for 0.5 min, then increased to 250 °C at a rate of 15 °C / min and maintained at that temperature for 1 min; the detector temperature was 250 °C; and the program run time was 11.5 min.

[0042] Example 2

[0043] The difference between Example 2 and Example 1 is that the preparation method of MF based on MOFs modification of the present invention comprises the following steps:

[0044] In step (3), PVDF / MOFs slurry was prepared by fully dissolving 400 mg of PVDF in 10 mL of N,N-dimethylformamide, dispersing Ti-MIL-125 and Fe-MIL-101 in 10 mL of N,N-dimethylformamide at a mass ratio of 1:2 to a concentration of 40 mg / mL, and then mixing the two and stirring at room temperature for 40 min.

[0045] In step (4), MF / PVDF / MOFs were prepared by taking 0.4 mL of the above slurry and dropping it onto each MF cube. The slurry was squeezed repeatedly to make the slurry evenly distributed on the MF, and dried at 100 °C for 16 h to completely fix the MOFs on the MF to obtain MOFs-modified MF, i.e., MF / PVDF / MOFs.

[0046] Example 3

[0047] The difference between Example 3 and Example 1 is that: in step (3), PVDF / MOFs slurry is prepared: 400 mg of PVDF is fully dissolved in 10 mL of N,N-dimethylformamide, Ti-MIL-125 and Fe-MIL-101 are dispersed in 10 mL of N,N-dimethylformamide at a mass ratio of 1:2, and the concentration is 40 mg / mL, and then the two are mixed and stirred at room temperature for 60 min;

[0048] In step (4), MF / PVDF / MOFs were prepared by taking 0.4 mL of the above slurry and dropping it onto each MF cube. The slurry was squeezed repeatedly to make the slurry evenly distributed on the MF, and dried at 60 °C for 8 h to completely fix the MOFs on the MF to obtain MOFs-modified MF, i.e., MF / PVDF / MOFs.

[0049] Test Example 1

[0050] Preparation of MF / PVDF / MOFs and characterization of experimental results

[0051] MF was cut into 1 × 1 × 1 cm cubes with an average mass of approximately 8.0 ± 0.2 mg. MOFs were immobilized on MF using the drop-coating method described above, using PVDF as a crosslinker. After MOF modification, the mass of each small cube increased to 15.2 ± 0.3 mg, which is consistent with the amount of MOFs added (20 mg / mL, 0.4 mL), indicating only a small amount of material loss during drying. The dried MF / PVDF / MOFs solution requires no additional processing and can be directly packed into a 1 mL pipette tip. To maintain good reproducibility, the upper and lower ends of the MF material were positioned as close to the same position on the pipette tip as possible during filling to minimize errors caused by packing density.

[0052] The morphologies of Fe-MIL-101, Ti-MIL-125, MF and MF / PVDF / MOFs were characterized by SEM. Figure 3 Fe-MIL-101 exhibited an octahedral structure, while Ti-MIL-125 exhibited a disc-like structure. The unmodified MF exhibited a three-dimensional porous network structure, while the MF surface was smooth. After MOF modification, disc-like and octahedral structures were clearly visible within the MF fibers and voids, demonstrating successful MOF immobilization on the MF.

[0053] The functional groups and chemical bond structures of Fe-MIL-101, Ti-MIL-125 powders and MF before and after modification with MOFs were analyzed by FT-IR. Figure 4). MF without any modification has only the bending vibration of the triazine ring of MF at 810 cm-1. Fe-MIL-101 has the bending vibration of the triazine ring at 545 cm-1. -1 There is a characteristic Fe-O peak at 1389 cm -1 and 1592cm -1 The stretching vibration of CO exists at 3429 cm. This indicates the successful synthesis of MIL-101-Fe. -1 The stretching vibration of MF / PVDF / MOFs is attributed to the OH groups introduced by water molecules. The presence of an O-Ti-O absorption band at 400-800 cm⁻¹ indicates the successful synthesis of MIL-101-Ti. The presence of Fe-O and Ti-O-Ti characteristic peaks in the MF / PVDF / MOFs spectrum indicates the successful immobilization of both MOFs on MF.

[0054] The crystal structure of the material was verified by XRD. Figure 5 The XRD pattern of Fe-MIL-101 shows clear diffraction peaks at 9.4°, 12.6°, 16.2°, 18.8°, and 22.0° on 2θ. The XRD pattern of Ti-MIL-125 shows diffraction peaks at 6.8°, 9.7°, 11.6°, 16.6°, 17.9°, and 19.5° on 2θ. These results are consistent with those of most previous studies, indicating the successful synthesis of Fe-MIL-101 and Ti-MIL-125. MF itself has no crystalline structure, but after being modified with MOFs, the diffraction peaks of Fe-MIL-101 and Ti-MIL-125 appeared, indicating that both MOFs materials were successfully modified on MF.

[0055] Test Example 2

[0056] Application of MF / PVDF / MOFs in the extraction of organophosphorus pesticides

[0057] A 5 mL sample containing a standard mixture of dimethoate (DMT), parathion-methyl (PAM), Iprobenfos (IBF), and chlorpyrifos (CPF) was prepared in pure water and adjusted to a pH of approximately 4.0 with 10 mM acetic acid. The pipette tip, loaded with MF / PVDF / MOFs, was connected to a syringe and cleaned with 1 mL of methanol and 1 mL of deionized water before use. The sample was then passed through the pipette tip into the syringe and then withdrawn as a single extraction cycle, thereby adsorbing the organophosphorus pesticides onto the material. Similarly, elution was performed directly with 0.5 mL of methanol via a pipette. The eluate was filtered through a 0.22 μm organic filter membrane and analyzed by GC-FTD.

[0058] Test Example 3

[0059] Selection and optimization of filling materials

[0060] The effects of the original MF, MF modified with PVDF, and MF modified with Fe-MIL-101, Ti-MIL-125, and MF modified with two MOFs materials at the same time in extracting mixed standards of organophosphorus pesticides were compared. As shown in the figure, the experiment found that the MF without any modification had poor extraction effects on the four organophosphorus pesticides, and the recovery rates were all below 20%. After the modification of PVDF, the extraction effect was partially improved due to the provision of richer pore size results, and the recovery rates of the three organophosphorus pesticides CPF, IBF, and PAM increased to about 30%. After the MOF material was modified, the extraction effect was significantly improved. Among them, Ti-MIL-125 had a better effect on IBF, with a recovery rate of more than 90%; while Fe-MIL-101 had a better effect on PAM and CPF. Therefore, it is considered to combine the advantages of the two to further improve the recovery rate ( Figure 6 ).

[0061] Fe-MIL-101 and Ti-MIL-125 have different pore structures. By compounding, the advantages of the two can be combined to improve the recovery rate. The addition ratio of Fe-MIL-101 and Ti-MIL-125 was optimized, and a better effect was achieved when the mass concentration ratio was 2:1. At the same time, the total concentration of the material added to each MF small cube was optimized. When the drop concentration was greater than or equal to 20 mg / mL (0.4mL), the MOF loading on the MF could reach a more uniform state and was not easy to fall off. However, when the concentration was too high, it was not easy to dry and it was easy to agglomerate on the MF surface and difficult to disperse. Therefore, the MOF addition concentration of the prefabricated slurry was set to 20 mg / mL ( Figure 7 ).

[0062] In order to facilitate the implementation of the PT-SPE procedure, MF / PVDF / MOF needs to be directly stuffed into the gun tip, and the filling amount of the material and the compactness of the filling also have a great influence on the extraction effect and recovery rate. By filling the same mass of MF in a fixed position of the gun tip, the error can be relatively reduced. The mass of the filling material was optimized. It was found that a good extraction can be achieved when the mass is 15 mg, that is, the mass of a cube. When too much is filled, the back pressure during the sample flow process is too high, and the channel is easily blocked, which is not only more time-consuming and labor-intensive, but also leads to a decrease in the extraction effect ( Figure 8 ).

[0063] Test Example 4

[0064] Optimization of extraction conditions

[0065] (1) pH

[0066] The pH conditions during extraction were optimized. Considering that organophosphorus pesticides are easily degraded under alkaline conditions, only the recovery rate at pH 3.0-8.0 was considered. The recovery rate reached the highest at pH 4.0 ( Figure 9 ).

[0067] (2) Salt concentration

[0068] The effects of 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, and 1 mol / L sodium chloride solutions on the recovery of organophosphorus pesticides were compared. The experimental results showed that the addition of salt concentration had little effect on IBF and CPF, but the recovery of DMT and PAM decreased with increasing salt concentration. Therefore, no additional salt ions were added in this experiment ( Figure 10 ).

[0069] (3) Number of extractions and elutions

[0070] The number of extraction and elution cycles was optimized for 5 mL of PT-SPE with an initial concentration of 20 μg / L. A higher recovery rate was achieved when the number of extractions was 7 and the number of elutions was 9. The entire PT-SPE process took a shorter time ( Figure 11 ).

[0071] (4) Type of elution reagent and volume of elution solution

[0072] The type of elution reagent and the volume of the eluent determine the elution effect of the target. The elution effects of methanol, acetone, and ethyl acetate were compared. The elution effect of ethyl acetate is relatively poor. Acetone has a better elution effect on CPF, but the recovery rate of N,N-dimethylformamide is only 40%. For the safety of the reagent and the comparison of the elution effect, methanol was selected as the elution solvent. When the elution volume is 0.5 mL, a higher recovery rate can be achieved. When the volume is greater than 0.5 mL, the recovery rate does not increase. Therefore, in order to save organic solvents and obtain a larger enrichment multiple, the elution volume is selected as 0.5 mL ( Figure 12 ).

[0073] Test Example 5

[0074] Constructing a standard curve

[0075] A 200 mg / L stock solution of the four organophosphorus pesticides was prepared in methanol and stored in a -20°C refrigerator. Before each use, the stock solution was diluted with methanol to a 2 mg / L working solution (for use on the same day). To generate a standard curve, the 2 mg / L working solution was diluted with methanol to create 5 mL standard solutions of 0.1 μg / L, 0.5 μg / L, 5 μg / L, 20 μg / L, 40 μg / L, 80 μg / L, 120 μg / L, and 160 μg / L. Rapid extraction was performed using a PT-SPE procedure, followed by elution with 0.5 mL of methanol. The eluate was filtered through a 0.22 μm organic filter membrane and analyzed by GC-FTD.

[0076] As shown in Table 1, the linear range of this method is 0.5~160.0 μg / L, and the determination coefficient (R 2 ) was between 0.9901 and 0.9979, the LOD (3 times the signal-to-noise ratio) was between 0.03 and 0.14 μg / L, the LOQ (10 times the signal-to-noise ratio) was between 0.1 and 0.5 μg / L, and the intra-day and inter-day RSDs were both less than 9.9%. The RSDs of MF / PVDF / MOFs synthesized in different batches were less than 9.1%, indicating that the method has good reproducibility.

[0077] Table 1 Analysis parameters of PT-SPE method

[0078]

[0079] Test Example 6

[0080] Detection of organophosphorus pesticides in actual samples

[0081] Under the above-mentioned optimal pretreatment conditions, OPPs in three samples, namely celery, cabbage and citrus, were analyzed to verify the effectiveness of the method. The experimental results are shown in Table 2. PAM and CPF were detected in cabbage, and CPF was detected in citrus, but the concentrations were all below LOQ. In order to further verify the accuracy of the method, spike recovery experiments were carried out on these actual samples. At spike levels of 20.0 μg / kg and 100.0 μg / kg, the spike recovery rates and RSDs were calculated by PT-SPE-GC-FTD analysis. As shown in the experimental results in Table 3-3, the spike recovery rates of these three target substances were between 75.3% and 118.8%, and the RSDs were all less than 9.6%. The determination of OPPs in actual samples by PT-SPE method (n=3) is shown in Table 2:

[0082] Table 2 Detection of actual samples by PT-SPE method

[0083]

[0084] Note: Recovery rate a : Recovery rate of spiked 20.0 μg / kg; Recovery rate b : Recovery of spiked sample at 100.0 μg / kg.

[0085] Comparative Example 1

[0086] Comparison with other extraction methods

[0087] In this work, two MOFs were fixed to MF using PVDF as a crosslinker. After extrusion and drying, the materials were filled into a pipette tip to achieve rapid extraction of organophosphorus pesticides. Compared to traditional SPE extraction columns, this PT-SPE column is easy to load and has high extraction efficiency. Compared with magnetic solid-phase extraction (MSP) and dispersive solid-phase extraction (DSPE), the PT-SPE method saves material collection time and avoids material loss during the collection process. Furthermore, analysis and detection using PT-SPE-GC-FTD can achieve high recoveries and low detection limits for multiple target compounds.

[0088] Table 3 Comparison with other extraction methods

[0089]

[0090] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above-mentioned test examples. The above-mentioned test examples and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications are possible without departing from the spirit and scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims, the description, and their equivalents.

Claims

1. A method for preparing MOFs modified melamine foam, characterized in that The steps include: (1) Pretreatment of melamine foam material: cut the foam into 1×1×1 cm cubes, clean it with ethanol ultrasonically, dry it, and set aside; (2) Synthesis of Ti-MIL-125 and Fe-MIL-101: Terephthalic acid and tetrabutyl titanate were dissolved in N,N-dimethylformamide and methanol, with the molar ratio of terephthalic acid to tetrabutyl titanate being 3:2 and the volume ratio of N,N-dimethylformamide to methanol being 9:1; the mixture was then transferred to a high-temperature and high-pressure reactor and heated at 150°C to obtain Ti-MIL-125; terephthalic acid and FeCl3·6H2O were dissolved in N,N-dimethylformamide at a molar ratio of 1:2, with the concentration of terephthalic acid being 0.075 mol / L and the concentration of FeCl3·6H2O being 0.15 mol / L, and heated at 110°C for 24 h to obtain Fe-MIL-101; Ti-MIL-125 and Fe-MIL-101 were washed three times with N,N-dimethylformamide and methanol and dried; (3) Preparation of PVDF / MOFs slurry: PVDF was dissolved in N,N-dimethylformamide solution at a concentration of 40 mg / mL, and Ti-MIL-125 and Fe-MIL-101 were dispersed in N,N-dimethylformamide at a mass ratio of 1:

2. The total concentration of Ti-MIL-125 and Fe-MIL-101 was 40 mg / mL. The two were then mixed and stirred at room temperature for 30-60 min. (4) Preparation of MF / PVDF / MOFs: The above slurry was added dropwise to each small foam cube, and squeezed repeatedly to make the slurry evenly distributed on the base material, and dried at a temperature of 60-100 °C for 8-16 h to prepare MF / PVDF / MOFs.

2. The method for preparing MOFs-modified melamine foam according to claim 1, wherein: In step (2), Ti-MIL-125 and Fe-MIL-101 are synthesized by dissolving 0.996 g of terephthalic acid and 1.36 g of tetrabutyl titanate in 36 mL of N,N-dimethylformamide and 4 mL of methanol, and then transferring the mixture to a high-temperature and high-pressure reactor and heating it at 150°C for 24 h to obtain Ti-MIL-125; dissolving 0.498 g of terephthalic acid and 1.62 g of FeCl3·6H2O in 40 mL of N,N-dimethylformamide and heating it at 110°C for 24 h to obtain Fe-MIL-101; Ti-MIL-125 and Fe-MIL-101 are washed three times with N,N-dimethylformamide and methanol, and then dried.

3. The method for preparing MOFs-modified melamine foam according to claim 2, wherein: In step (3), PVDF / MOFs slurry was prepared: PVDF was fully dissolved in N,N-dimethylformamide to a solubility of 40 mg / mL; Ti-MIL-125 and Fe-MIL-101 were dispersed in N,N-dimethylformamide at a mass ratio of 1:2 to a total concentration of 40 mg / mL, and then the two were mixed and stirred at room temperature for 30 min.

4. The method for preparing MOFs-modified melamine foam according to claim 2, wherein: In step (4), MF / PVDF / MOFs were prepared by taking 0.4 mL of the above slurry and dropping it onto each foam block. The slurry was squeezed repeatedly to make it evenly distributed, and then dried at 80 °C for 12 h to completely fix the MOFs on the foam to prepare MF / PVDF / MOFs.

5. MOFs modified melamine foam prepared by the preparation method according to any one of claims 1 to 3.

6. Use of the MOFs modified melamine foam according to claim 5 in the solid phase extraction of organophosphorus pesticides by a gun tip.

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