A covalent organic framework-based needle-trap microextraction device and a preparation method thereof

Abstract

The application discloses a kind of needle trap microextraction device based on covalent organic framework and preparation method thereof, and specific preparation steps are as follows: stainless steel wire fiber pretreatment, preparation of covalent organic framework material and sol-gel solution, then stainless steel wire is immersed in sol-gel solution, extracted and placed in covalent organic framework powder, solidified, to obtain the fiber coated with covalent organic framework coating, finally the fiber is inserted into stainless steel needle and fixed to obtain needle trap microextraction device. The device is used to enrich trace polychlorinated biphenyl in milk, combined with gas chromatograph, and the detection sensitivity of polychlorinated biphenyl is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of sample pretreatment technology, and specifically provides a needle trap microextraction device and its preparation method using stainless steel wire fiber as the substrate and a covalent organic framework coating as the extraction phase. Background Technology

[0002] Polychlorinated biphenyls (PCBs) are a class of toxic, persistent organic pollutants with teratogenic, carcinogenic, and mutagenic effects. Due to their chemical stability, insulating properties, and non-flammability, PCBs have been widely used in various chemical industries, including rubber, plastics products, fuels, pigments, and carbonless copy paper. Once in an ecosystem, PCBs are difficult to biodegrade and have long retention times, accumulating in organisms through the food chain. Skin contact with PCBs can easily lead to skin diseases such as acne and rashes. Ingestion of meat, fish, and dairy products highly contaminated with PCBs can easily cause damage to the nervous, reproductive, and immune systems. Therefore, there is an urgent need to develop a highly sensitive, selective, simple, and environmentally friendly method for detecting PCBs in the environment. However, the actual sample matrix is ​​complex, and PCBs are present at trace levels within it. Therefore, direct instrumental detection is difficult and may even damage the instrument. Appropriate sample pretreatment methods are needed to purify and concentrate the analytes to remove matrix interferences and improve detection sensitivity and accuracy.

[0003] Needle trap microextraction (NTM) is a highly efficient sample preparation technique based on the theory of solid phase microextraction (SPME). It boasts advantages such as simple operation, low cost, miniaturized equipment, automation, environmental friendliness, and high efficiency, and has been applied in various fields including environment, food, and biology for the detection of volatile or semi-volatile compounds. The core of the needle trap microextraction device (NTM) lies in the adsorbent or coated fiber filled within a specially designed stainless steel needle. Compared to SPME, this effectively prevents coating detachment, contributing to a longer device lifespan. Furthermore, it increases the volume of the extraction phase, improving extraction efficiency, while dynamic sampling allows for complete extraction of the target analyte. The extraction medium is a crucial factor affecting NTD extraction performance; selecting a suitable adsorbent can lead to good recovery rates and high enrichment rates. Covalent organic frameworks (COFs) are a new type of nanoporous materials composed of light elements (C, H, O, N, and B, etc.) linked by strong covalent bonds. They have advantages such as permanent porosity, good thermal stability, physicochemical stability, low framework density, adjustable pore size, and large specific surface area. In recent years, they have been widely used in gas adsorption, catalysis, photoelectric sensing, and other fields. As a novel extraction material, they have also attracted great attention in the field of sample pretreatment. Summary of the Invention

[0004] The purpose of this invention is to provide a needle trap microextraction device based on a covalent organic framework and its preparation method.

[0005] The objective of this invention is achieved through the following technical solution: S1. Immerse a stainless steel wire (5cm, 0.3mm) in a methanol solution and sonicate for 15 minutes to remove impurities from the fiber surface. Then dry it at room temperature. After drying, immerse the stainless steel wire in hydrofluoric acid for etching for 30 minutes. Rinse it multiple times with ultrapure water and dry it at room temperature for later use. S2,2,4,6-tricarboxymethyl phloroglucinol (TP, 0.2 mmol, 45.33 mg) and 1,3,5-tris(4-aminophenoxy)benzene (TAPOB, 0.2 mmol, 80.69 mg) were dissolved sequentially in a mixed solution of 1,3,5-trimethylbenzene and 1,4-dioxane (1:1, v / v, 6 ml). After sonication for 10 min, a homogeneous solution was obtained. Then, 600 μL of glacial acetic acid solution was slowly added, and the mixture was vortexed for 5 min. Finally, the mixed solution was transferred to a high-pressure reactor and reacted at 120 °C for 72 h. After the reaction was completed, the orange-yellow solid was collected by filtration and centrifugation. Unreacted ligands were removed by repeated ultrasonic washing with acetone. The collected powder was vacuum dried overnight at 60 °C to obtain TP-TAPOB COF material. S3. A sol-gel solution was obtained by vortexing 100 μL of a mixed solution of dichloromethane, 100 μL of methyltrimethoxysilane, 100 μL of hydroxyl-terminated polydimethylsiloxane, and 60 μL of 95% trifluoroacetic acid for 5 min. A pretreated stainless steel wire was inserted into the gel solution and quickly withdrawn. This process was repeated several times to form a uniform gel coating on the wire surface. The wire was then placed in 3 mg of TP-TAPOB COF powder and rotated, with the coating process repeated three times. The wire was then aged in a 260°C oven for 4 h. Finally, the coated fiber was longitudinally inserted into a stainless steel needle (60 mm × 0.52 mm id, 0.81 mm od) to create a needle-trap microextraction device.

[0006] The beneficial effects of this invention are: 1. The TP-TAPOB COF material prepared by this invention has a simple preparation method, high thermal stability, and strong solvent resistance; 2. TP-TAPOB COF material achieves specific adsorption of target analytes through π-π stacking and hydrophobic interactions, with high extraction efficiency and good selectivity, enabling quantitative detection of PCBs in milk matrix. Attached Figure Description

[0007] Figure 1 The infrared spectrum of the TP-TAPOB COF is shown below. Figure 2The XRD patterns of the TP-TAPOB COF in different solvents are shown below. Figure 3 SEM images of the bare stainless steel wire fibers and TP-TAPOB COF coated fibers; Figure 4 Thermogravimetric analysis curves of TP-TAPOB COF and fiber coating; Figure 5 The extraction chromatogram of PCBs in milk by the TP-TAPOB COF needle trap microextraction device prepared in this invention. Figure 6 This is a comparison chart of the extraction effects of TP-TAPOB COF coated fibers and sol-gel coated fibers. Implementation

[0008] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field. Example

[0009] The preparation method of the device described in this embodiment is as follows: A stainless steel wire (5 cm, 0.3 mm) is immersed in a methanol solution and sonicated for 15 min to remove impurities from the fiber surface. After drying at room temperature, the dried stainless steel wire is immersed in hydrofluoric acid for etching for 30 min, then rinsed multiple times with ultrapure water to obtain pretreated fibers, which are then dried at room temperature for later use. 2,4,6-Trimethylol-Resorcinol (TP, 0.2 mmol, 45.33 mg) and 1,3,5-Tris(4-aminophenoxy)benzene (TAPOB, 0.2 mmol, 80.69 mg) are dissolved sequentially in a mixed solution of 1,3,5-trimethylbenzene and 1,4-dioxane (1:1, v / v, 6 mL). The solution is placed in a 15 mL centrifuge tube and sonicated for 10 min to obtain a uniform dispersion. Then, glacial acetic acid solution (600 μL, 6 mol / L) is slowly added to the mixture, and the mixture is vortexed for 5 min. Finally, the mixed solution was transferred to a high-pressure reactor and reacted at 120°C for 72 hours. After the reaction was completed, the orange-yellow solid was collected by filtration and centrifugation. Unreacted ligands were removed by repeated ultrasonic cleaning with acetone. The collected powder was vacuum dried overnight at 60°C to obtain TP-TAPOB COF material.

[0010] 100 μL of dichloromethane, 100 μL of methyltrimethoxysilane, 100 μL of hydroxyl-terminated polydimethylsiloxane, and 60 μL of 95% trifluoroacetic acid were vortexed for 5 min to obtain a sol-gel solution. A pretreated stainless steel wire was inserted into the gel solution and quickly withdrawn. This process was repeated several times to form a uniform gel coating on the wire surface. The wire was then placed in 3 mg of TP-TAPOB COF powder and rotated, with the coating repeated three times. The mixture was then aged in a 260℃ oven for 4 h to obtain a uniformly coated TP-TAPOB coating. Finally, the coated fiber was longitudinally inserted into a stainless steel needle (60 mm × 0.52 mm id, 0.81 mm od) to obtain a needle-trap microextraction device.

[0011] The functional groups, solvent stability, morphology, structure, and thermal stability of the prepared TP-TAPOB COF were characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis.

[0012] like Figure 1 As shown, compared with its monomers TP and TAPOB, the NH stretching vibrations of TAPOB in the FT-IR spectrum of TP-TAPOB COF (3420, 3340, 3200 cm⁻¹) are significantly different. -1 The peaks (C=O, C=C) disappeared significantly. Furthermore, a C=O peak appeared in the FT-IR spectrum of TP-TAPOB, while the C=C peak disappeared, and a peak appeared at 1220 cm⁻¹. -1 Typical CN stretch bands appeared at the site, indicating that TP and TAPOB successfully condensed.

[0013] Figure 2 The XRD patterns of TP-TAPOB COF after treatment with 1 mol / L HCl, 1 mol / L NaOH, acetone, and methanol for 3 days are shown in the figure. As shown, the XRD patterns of TP-TAPOB COF treated with the four different solvents are basically consistent with those of TP-TAPOB COF without any solvent treatment, indicating that TP-TAPOB COF has good solvent stability.

[0014] like Figure 3 a and b are SEM images of bare stainless steel wire fibers (100x magnification) and TP-TAPOB COF coated fibers (100x magnification), respectively. Figure 3 As can be seen from ab, the surface of the original steel wire fiber is smooth, while the surface of the coated steel wire fiber is rough and porous. Its porous structure effectively improves the extraction capacity of the device. Figure 4The thermogravimetric analysis (TGA) of the TP-TAPOB COF sol-gel coating shows that the coating weight loss is approximately 10% when the temperature is below 400℃, indicating that the fiber coating prepared in this experiment has excellent thermal stability below 400℃. Example

[0015] This embodiment provides a method for extracting PCBs (PCB28, PCB52, PCB77, PCB118, PCB153) from milk using the TP-TAPOB COF-coated needle trap microextraction device described in Embodiment 1. The specific steps are as follows: Extraction of polychlorinated biphenyls (PCBs): In this experiment, the needle trap microextraction device prepared above was used for extraction of PCBs with a concentration of 100 μg·L⁻¹. - 1 PCB28, PCB52 and 200 μg·L -1 Five polychlorinated biphenyls (PCBs) in a mixed solution (PCB77, PCB118, and PCB153) were subjected to headspace extraction to investigate the extraction capability of the device. Specifically, a 1 g / L mixed standard solution of the five PCBs was prepared using acetone, then spiked into 20 mL of milk. The solution was transferred to a sealed sample vial with a PTFE cap for subsequent extraction. The needle trap microextraction device was connected to a flexible tube at one end of a peristaltic pump, and the other end of the pump was connected to an empty needle. The empty needle was inserted below the liquid surface, and the extraction needle was positioned 1 cm above the liquid surface. After starting the peristaltic pump, the gas in the sample vial flowed through the extraction needle into the empty needle at the other end, forming a dynamic gas circulation pathway. The device was used for extraction at a constant temperature (80℃) for 40 min. After extraction, the extraction device was removed, and a 1 mL standard airtight syringe was connected and directly inserted into the gas chromatograph inlet for 5 min. Thermal desorption was performed under nitrogen assistance, and the gas entered the chromatographic column for separation and analysis.

[0016] Gas chromatography analysis conditions: An Agilent 7890B gas chromatograph was used for gas chromatography analysis. The chromatographic separation column used was an HP-5 capillary column (30 mm × 0.32 mm id × 0.25 μm); high-purity nitrogen (99.999%) was used as the carrier gas; splitless injection mode was used; the injection port temperature was 270℃; the temperature program was as follows: the initial temperature of the column oven was 70℃, first increased to 200℃ at 20℃ / min, then increased to 280℃ at 5℃ / min, and held for 5 min; the FID detector temperature was 300℃.

[0017] like Figure 5 As shown, with the addition of 100 μg·L -1 PCB28, PCB52 and 200 μg·L -1 Five polychlorinated biphenyls (PCBs) were detected in milk samples (PCB77, PCB118, and PCB153). No PCBs chromatograms were observed in unspecified samples.

[0018] Comparative Example 1: To demonstrate the effect of TP-TAPOB COF coating on PCB extraction efficiency, a sol-gel coated needle trap microextraction device was prepared in this comparative example: a stainless steel wire (5 cm, 0.3 mm) was immersed in methanol solution and ultrasonically cleaned for 15 min to remove surface impurities, then dried at room temperature. The dried stainless steel wire was then etched in hydrofluoric acid for 30 min, followed by multiple rinses with ultrapure water to obtain pretreated fibers, which were then dried at room temperature for later use. 100 μL of dichloromethane, 100 μL of methyltrimethoxysilane, 100 μL of hydroxyl-terminated polydimethylsiloxane, and 60 μL of 95% trifluoroacetic acid were vortexed for 5 min to obtain a sol-gel solution. The pretreated stainless steel wire was inserted into the gel solution and quickly withdrawn, repeated several times to form a uniform gel coating on the wire surface, thus obtaining sol-gel coated fibers. These fibers were then inserted into stainless steel needles to create a needle trap microextraction device. This device, along with the covalent organic framework-based needle trap microextraction device from Example 1, was used to extract polychlorinated biphenyls (PCBs) from milk. The results are as follows: Figure 6 As shown, the TP-TAPOB COF needle trap microextraction device significantly increases the extraction efficiency of PCBs, indicating that TP-TAPOB COF has a good adsorption effect on PCBs.

Claims

1. A method for preparing a needle-trap microextraction device based on a covalent organic framework, characterized in that, The steps are as follows: S1. Immerse the stainless steel wire in methanol solution and sonicate for 15 minutes to wash away impurities on the fiber surface. Then dry it at room temperature. After drying, immerse the stainless steel wire in hydrofluoric acid for 30 minutes to etch it. Then rinse it with ultrapure water several times and dry it at room temperature for later use. S2. 2,4,6-Tricarboxymethyl phloroglucinol and 1,3,5-tris(4-aminophenoxy)benzene were dissolved sequentially in 6 ml of a mixed solution of 1,3,5-trimethylbenzene and 1,4-dioxane. After sonication for 10 min, a homogeneous solution was obtained. Then, 600 μL of glacial acetic acid solution was slowly added, and the mixture was vortexed for 5 min. Finally, the mixed solution was transferred to a high-pressure reactor and reacted at 120 °C for 72 h. After the reaction was completed, the orange-yellow solid was collected by filtration and centrifugation. Unreacted ligands were removed by repeated ultrasonic washing with acetone. The collected powder was vacuum dried overnight at 60 °C to obtain TP-TAPOB COF material. S3. Vortex a mixed solution of 100 μL dichloromethane, 100 μL methyltrimethoxysilane, 100 μL hydroxyl-terminated polydimethylsiloxane and 60 μL 95% trifluoroacetic acid for 5 min to mix thoroughly, and obtain a sol-gel solution; insert the pretreated stainless steel wire into the above gel solution, quickly pull out the wire, repeat several times to form a uniform gel coating on the surface of the wire; The steel wire was then placed in TP-TAPOB COF powder and rotated. The coating was repeated three times. After the coated fiber was aged at 260°C for 4 hours, it was longitudinally inserted into a stainless steel needle to obtain a needle trap microextraction device.

2. The preparation method according to claim 1, characterized in that, The stainless steel wire described in S1 has a diameter of 0.3 mm and a length of 5 cm.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the two monomers, 2,4,6-tricarboxymethyl phloroglucinol and 1,3,5-tris(4-aminophenoxy)benzene, in S2 is 0.2 mmol:0.2 mmol.

4. The preparation method according to claim 1, characterized in that, The volume ratio of the two solvents, 1,3,5-trimethylbenzene and 1,4-dioxane, in S2 is 1:

1.

5. The preparation method according to claim 1, characterized in that, The molar concentration of the glacial acetic acid solution mentioned in S2 is 6 mol / L.

6. The preparation method according to claim 1, characterized in that, The stainless steel needle described in S3 is a specially made stainless steel needle that can be matched with the gas chromatograph injection port, with a length of 60 mm, an inner diameter of 0.52 mm, and an outer diameter of 0.81 mm.

7. A needle trap microextraction device based on a covalent organic framework, characterized in that, Prepared using any one of the preparation methods of claims 1 to 6, and used for the extraction of trace organic polychlorinated biphenyls from milk.

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