Hydrazone COF-based solid phase microextraction fiber and its preparation method and application

Abstract

The present invention discloses a hydrazone COF-based solid phase microextraction fiber and a preparation method and application thereof, which involves preparing a covalent organic framework material (BTCH-PTA-COF), fixing it on the end of a stainless steel wire by a sol-gel method, aging it at a gas chromatography injection port until a stable baseline is obtained, and using it for headspace solid phase microextraction (HS-SPME) of five PAHs. The BTCH-PTA-COF fiber prepared by the present invention has good thermal stability, large specific surface area, suitable pore size, π-π stacking effect, and hydrophobic effect, which has good enrichment efficiency for PAHS.

Description

Technical Field

[0001] The invention relates to the technical field of analytical chemistry and sample pretreatment, and in particular to the preparation of a hydrazone COF-based solid phase microextraction fiber and the high-enrichment extraction of polycyclic aromatic hydrocarbons by the fiber. Background Art

[0002] Persistent organic pollutants (POPs) are not easily degraded by nature, can exist in the environment for a long time, and are highly fat-soluble and semi-volatile, which makes them distributed all over the world and easy to accumulate through the food chain. Polycyclic aromatic hydrocarbons (PAHs) are a class of highly inert organic pollutants composed of two or more condensed aromatic rings, mainly from the incomplete combustion of coal, oil, tobacco, and food processing and preparation (frying, grilling, etc.). Studies have shown that PAHs have carcinogenic, teratogenic, and mutagenic effects and can directly enter the human body through the food chain. Although the concentration of PAHs in food is very low, long-term accumulation poses a great threat to human health and is listed in the list of priority persistent pollutants by the European Union and the US Environmental Protection Agency. At present, tea drinks and barbecue are two popular beverages and snacks for people all over the world. Using open flames to dry tea leaves is usually part of tea processing, which may lead to the production and accumulation of PAHs in tea leaves. Some studies have shown that 8% of the total PAHs content (depending on the type of tea and brewing conditions) can be transferred from dry tea leaves to hot water during the brewing process. In addition, barbecue is also made by burning charcoal, which may lead to the accumulation of PAHs in barbecue. PAHs are often present in food at ultra-trace and trace levels. Therefore, detecting the content of PAHs in food is crucial to human health.

[0003] At present, there are many methods for detecting PAHs, mainly including gas chromatography (GC), liquid chromatography (HPLC), gas chromatography tandem mass spectrometry (GC-MS), etc. However, the content of PAHs in food is low and the matrix is ​​complex, so it is difficult for the above instruments to detect directly. Solid phase microextraction (SPME) is a green, solvent-free sample pretreatment and enrichment technology that integrates sampling, purification, enrichment, and injection, and can be used in conjunction with GC, HPLC, and GC-MS. The principle of SPME is based on the equilibrium distribution of the target analyte between the fiber coating and the sample matrix. Therefore, the fiber coating is a key part that is directly related to the selectivity, sensitivity, and application of the SPME method. The solid phase microextraction fiber is the core component of solid phase microextraction technology, consisting of two main parts: the matrix and the coating. The development of a solid phase microextraction fiber coating that can effectively enrich PAHs is extremely important for the detection of trace PAHs. Summary of the invention

[0004] One of the purposes of the present invention is to synthesize a reusable solid phase microextraction fiber with good thermal stability and large specific surface area; the second purpose is to provide a detection method for PAHS with a wide linear range, good sensitivity and high enrichment factor.

[0005] In order to achieve the above object, the present invention adopts the following scheme:

[0006] The hydrazone COF-based solid phase microextraction fiber comprises a fiber carrier and an extraction coating, wherein the extraction coating is attached to the surface of the fiber carrier, and the extraction coating contains BTCH-PTA-COF, and the BTCH-PTA-COF is prepared by the following method:

[0007] BTCH-PTA-COF was synthesized by heating reflux method with 1,3,5-benzenetricarboxylic acid hydrazide and terephthalaldehyde as monomers, 1,4-dioxane and 1,3,5-trimethylbenzene as solvents and acetic acid as catalyst. The whole reaction was kept under nitrogen protection.

[0008] The preparation method of solid phase microextraction fiber specifically comprises the following steps:

[0009] (1) Preparation of BTCH-PTA-COF materials

[0010] BTCH-PTA-COF is synthesized by a heating reflux method using 1,3,5-benzenetricarboxylic acid hydrazide and terephthalaldehyde as monomers, 1,4-dioxane and 1,3,5-trimethylbenzene as solvents and acetic acid as a catalyst. The molar ratio of 1,3,5-benzenetricarboxylic acid hydrazide to terephthalaldehyde is 2:3. The entire reaction is maintained under nitrogen protection, the heating reflux temperature is 80-120°C, and the time is 12-48h.

[0011] Preferably, the heating reflux temperature is 90° C. and the time is 24 h.

[0012] (2) Preparation of BTCH-PTA-COF fibers

[0013] Stainless steel wire is used as a fiber carrier, BTCH-PTA-COF powder is dispersed in a gel sol solution, and a fiber coating is prepared by a sol-gel method. The gel sol solution is prepared from methyltrimethoxysilane, hydroxyl-terminated polysiloxane, dichloromethane and trifluoroacetic acid.

[0014] Specifically:

[0015] (201) The end of a stainless steel wire was corroded with aqua regia to obtain a rough surface;

[0016] (202) Gel sol solution was prepared using methyltrimethoxysilane, hydroxyl-terminated polysiloxane, dichloromethane as solvent, and trifluoroacetic acid as catalyst;

[0017] (203) BTCH-PTA-COF powder was weighed and dispersed into the above solution to obtain a uniform sol-gel COF solution by ultrasound. The pretreated stainless steel wire was vertically immersed in the sol-gel COF solution while rotating the solution to ensure uniform coating. The stainless steel wire was slowly taken out vertically and dried in an oven. The above steps were repeated 1–4 times until the desired coating thickness was obtained.

[0018] Application of solid phase microextraction fiber in trace detection of PAHs. Solid phase microextraction fiber enriches PAHs by extracting PAHs from the test solution, and then is used in conjunction with a PAHs detection device for the detection of PAHs.

[0019] The specific steps are:

[0020] The hydrazone COF-based solid phase microextraction fiber is placed above the test solution for extraction through headspace solid phase microextraction, and then inserted into the sampling port of the PAHs detection device for thermal desorption. After desorption, analysis and detection are performed, wherein the extraction time is 20-45min, the extraction temperature is 35-60°C, the stirring speed during the extraction process is 400-1200rpm, the desorption time is 1-6min, and the desorption temperature is 250-300°C.

[0021] The PAHs detection device is an existing PAHs detection device, including but not limited to gas chromatography, liquid chromatography, and gas chromatography-tandem mass spectrometry.

[0022] Compared with the prior art, the BTCH-PTA-COF prepared by the present invention has good thermal stability, a large specific surface area, a suitable pore size, π-π stacking effect and hydrophobic effect, and has a good enrichment efficiency for PAHS. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the TGA diagram of BTCH-PTA-COF of the present invention.

[0024] Figure 2 This is the FT-IR graph of BTCH-PTA-COF of the present invention.

[0025] Figure 3 These are SEM images of the stainless steel wire (A), BTCH-PTA-COF (B), and BTCH-PTA-COF fiber (C) prepared by the sol-gel method in the present invention treated with aqua regia.

[0026] Figure 4 This is the nitrogen adsorption-desorption isotherm diagram of BTCH-PTA-COF of the present invention.

[0027] Figure 5The chromatogram of the extraction of green tea spiked sample by BTCH-PTA-COF fiber of the present invention, wherein a: blank green tea sample, b: spiked 5 μg·L -1 ,c: spiked with 25 μg·L -1 ,d: spiked with 50 μg·L -1 . (1-naphthalene, 2-acenaphthene, 3-anthracene, 4-phenanthrene, 5-pyrene). DETAILED DESCRIPTION

[0028] The present invention is described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0029] Example 1: A method for preparing a BTCH-PTA-COF material, comprising the following steps:

[0030] 1,3,5-Benzenetricarboxylic acid hydrazide (BTCH) (0.2 mmol) and terephthalaldehyde (PTA) (0.3 mmol) were added to a round-bottom flask containing 15.0 mL 1,4-dioxane and 5.0 mL 1,3,5-trimethylbenzene. 1,4-dioxane is a polar solvent and 1,3,5-trimethylbenzene is a non-polar solvent. The combination of the two helps to disperse the monomers and regulate the polarity range of the reaction system, thereby facilitating the stable regulation of the equilibrium reaction of COF formation.

[0031] Then add 0.5mL 6.0mol·L -1 Acetic acid, then the entire round-bottom flask is immersed in an ultrasonic bath for 15 minutes. Finally, the mixture is heated and stirred at 90°C for 24 hours, and the entire reaction is maintained under nitrogen protection to obtain a yellow suspension, which is washed with 1,4-dioxane, THF and acetone in sequence, and then vacuum dried at 80°C to obtain BTCH-PTA-COF (COF represents covalent organic framework material), wherein 1,4-dioxane is used to wash away unreacted monomers, THF has an emulsifying effect and can wash away dirt, and acetone is both fat-soluble and water-soluble, and can wash away fat-soluble impurities and water-soluble impurities.

[0032] During the experiment, the reaction conditions were optimized, including reaction temperature (80, 90, 100, 110, 120°C) and reaction time (12h, 18h, 24h, 36h, 48h). The experimental results showed that the optimal temperature was 90°C and the optimal time was 24h.

[0033] The synthetic route is as follows:

[0034]

[0035] Example 2: Preparation of BTCH-PTA-COF fibers

[0036] First, a stainless steel wire with a length of 15 cm was etched with aqua regia (HCl / HNO3=3:1, v / v) to a length of about 5.0 cm at the end to make its surface rough, and the etched part of the stainless steel wire was washed with ethanol and ultrapure water in turn, and then naturally air-dried. Then, 100 μL of methyltrimethoxysilane (MTMOS) (precursor), 100 μL of hydroxyl-terminated polysiloxane (PDMS-OH) (stationary phase) and 100 μL of dichloromethane were mixed for about 5 min using a mixer, and 50 μL of trifluoroacetic acid (TFA) (catalyst) was added to the mixture, and the mixture was mixed for 2 min to obtain a sol-gel solution. 30 mg of BTCH-PTA-COF powder was dispersed in the above solution and ultrasonically obtained a uniform sol-gel COF solution. The pretreated stainless steel wire was vertically immersed in the sol-gel COF solution, and the solution was rotated to make it uniformly coated, and the stainless steel wire was slowly taken out vertically and dried in an oven. Repeat the above steps three times until the desired coating thickness was obtained at the end of the stainless steel wire (the thickness obtained in this embodiment was 23 μm).

[0037] Figure 1 The TGA diagram of BTCH-PTA-COF of the present invention is shown in FIG. As can be seen from the figure, the mass loss is 5% at 375° C., indicating that BTCH-PTA-COF has good thermal stability and can be used for thermal desorption of gas chromatography.

[0038] Figure 2 FT-IR diagram of BTCH-PTA-COF of the present invention. 3340cm -1 The peak at 1620 cm corresponds to the stretching vibration of the NH bond. -1 There is C=N stretching vibration at 1550cm -1 There is a peak of C=C at 1350cm -1 There is a CN bond stretching vibration absorption peak at , indicating the successful preparation of BTCH-PTA-COF

[0039] Figure 3 The SEM images of the stainless steel wire (A) treated with aqua regia, BTCH-PTA-COF (B), and BTCH-PTA-COF fiber (C) prepared by the sol-gel method in the present invention. The surface of the stainless steel wire treated with aqua regia is rough. BTCH-PTA-COF is in the form of fine fibers. Figure C shows that BTCH-PTA-COF is uniformly attached to the surface of the stainless steel wire.

[0040] Figure 4 The nitrogen adsorption-desorption isotherm of BTCH-PTA-COF of the present invention is shown in FIG. 2·g -1 , the pore size is 5.6 nm, which is conducive to the adsorption of PAHs.

[0041] Example 3: Processing of real samples

[0042] The green tea beverage was filtered through a 0.45 μm filter membrane and then refrigerated at 4°C for subsequent solid phase microextraction (SPME) experiments.

[0043] Example 4: SPME Process

[0044] Since PAHs are volatile, headspace solid phase microextraction (HS-SPME) was selected as the best extraction method. The specific steps are as follows:

[0045] (1) The BTCH-PTA-COF fiber coating loaded on the end of the stainless steel wire was aged at 280°C in the gas chromatography GC injection port until a stable baseline was obtained;

[0046] (2) the test solution is placed in an SPME sample bottle sealed by a polytetrafluoroethylene diaphragm, and then placed in a constant temperature water bath at 50°C, the micro syringe needle is inserted into the SPME sample bottle through the sample bottle diaphragm, the stainless steel wire treated in step (1) is inserted into the needle hole of the micro syringe, and then the BTCH-PTA-COF fiber coating is pushed out of the syringe into the headspace of the test solution to extract PAHs, and the stainless steel wire is extracted to retract the fiber into the syringe and take it out of the sample bottle;

[0047] (3) Finally, the BTCH-PTA-COF fiber coating after extraction was inserted into the GC injection port for thermal desorption, and then subjected to GC-FID analysis and detection. Before each extraction, the fiber was treated in the GC-FID injection port for 2 minutes to ensure that no chromatographic peaks appeared.

[0048] In order to obtain the best SPME efficiency, the main parameters affecting the SPME efficiency were optimized. The test solutions in the optimization process contained NaCl (different ionic strengths) and PAHs (50 μg·L -1 ) mixed standard solution. The optimized conditions include extraction time (20, 25, 30, 35, 40, 45min), extraction temperature (30, 40, 50, 60, 70℃), desorption time (1, 2, 3, 4, 5, 6min), desorption temperature (250, 260, 270, 280, 290, 300℃), stirring speed (400, 600, 800, 1000, 1200rpm), ionic strength (0, 5, 10, 15, 20, 25%) and pH (3, 4, 5, 6, 7, 8, 9, 10). The test solution in the optimization experiment was 50μg·L containing 5% NaCl. -1 Analysis of PAHs mixed standard solution.

[0049] Mixed standard stock solution: Accurately weigh 3.0 mg of naphthalene, acenaphthene, anthracene, phenanthrene, and pyrene respectively, dissolve them in acetonitrile and prepare 300 mg / L -1 The mixed standard stock solution was diluted step by step to obtain 5, 25, and 50 μg·L -1 PAHs mixed standard solution, all solutions were stored in a refrigerator at 4°C to prevent volatilization, and the solution was highly toxic, so be careful to avoid direct contact with all reagents. The experiment was carried out in a fume hood. All experiments were repeated 3 times.

[0050] The optimal extraction time was finally determined to be 30 min, the extraction temperature was 50 °C, the desorption time was 4 min, the desorption temperature was 270 °C, the stirring speed was 800 rpm, the ionic strength (NaCl concentration) was 10%, and the pH had no effect on the extraction conditions. The pH of the original sample solution was 7.4, so the pH was not adjusted in subsequent experiments.

[0051] Under the above-mentioned optimal extraction conditions, the green tea beverage filtered through a 0.45 μm filter membrane was placed in a sample bottle as the test solution in step (2), and then placed in a constant temperature water bath at 50°C. A self-assembled micro-syringe was used to penetrate the sample bottle diaphragm, and then the BTCH-PTA-COF fiber was pushed out of the syringe into the headspace of the sample solution. After extraction at 800 rpm and 40°C for 35 minutes, the fiber was retracted into the syringe and taken out of the sample bottle, inserted into the GC injection port, and thermally desorbed at 270°C for 2 minutes. GC-FID analysis was performed. The results are shown in Tables 1 and 2. Figure 5 shown.

[0052] Table 1

[0053]

[0054] Table 1 shows that BTCH-PTA-COF fiber combined with HS-SPME-GC-FID is a method for detecting PAHs with a wide linear range, good sensitivity, and high enrichment factor.

[0055] Figure 5 The chromatogram of the extraction of green tea spiked sample by BTCH-PTA-COF fiber of the present invention. Figure: a: blank green tea sample, b: spiked with 5 μg·L -1 ,c: spiked with 25 μg·L -1 ,d: spiked with 50 μg·L -1 (1-naphthalene, 2-acenaphthene, 3-anthracene, 4-phenanthrene, 5-pyrene). The good recovery rate shows that this method can be used for the detection of real samples.

[0056] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a hydrazone COF-based solid phase microextraction fiber, characterized in that: The specific steps include: (1) Preparation of BTCH-PTA-COF materials BTCH-PTA-COF was synthesized by heating reflux method using 1,3,5-benzenetricarboxylic acid hydrazide and terephthalaldehyde as monomers, 1,4-dioxane and 1,3, 5-trimethylbenzene as solvents, and acetic acid as catalyst. The molar ratio of 1,3,5-benzenetricarboxylic acid hydrazide to terephthalaldehyde was 2:

3. The entire reaction was maintained under nitrogen protection, and the heating reflux temperature was 90°C for 24 hours. (2) Preparation of hydrazone COF-based solid phase microextraction fiber Stainless steel wire was used as a fiber carrier, BTCH-PTA-COF powder was dispersed in a sol-gel solution, and the fiber coating was prepared by a sol-gel method. The sol-gel solution was prepared from methyltrimethoxysilane, hydroxyl-terminated polysiloxane, dichloromethane and trifluoroacetic acid.

2. The method for preparing the hydrazone COF-based solid phase microextraction fiber according to claim 1, characterized in that: Step (2) Preparation of hydrazone COF-based solid phase microextraction fiber is specifically as follows: (201) The end of a stainless steel wire was corroded with aqua regia to obtain a rough surface; (202) Sol-gel solutions were prepared using methyltrimethoxysilane, hydroxyl-terminated polysiloxane, and dichloromethane as solvents and trifluoroacetic acid as a catalyst; (203) Weigh BTCH-PTA-COF powder and disperse it into the above solution by ultrasonication to obtain a uniform sol-gel COF solution. Vertically immerse the stainless steel wire pretreated in step (201) into the sol-gel COF solution while rotating the solution to ensure uniform coating. Slowly take out the stainless steel wire vertically and dry it in an oven. Repeat the above steps 1-4 times until the desired coating thickness is obtained.

3. A hydrazone COF-based solid phase microextraction fiber prepared by the preparation method according to any one of claims 1 to 2.

4. Use of the hydrazone COF-based solid phase microextraction fiber according to claim 3 in the detection of PAHs, wherein the solid phase microextraction fiber enriches PAHs by extracting PAHs from the test solution, and then is used in conjunction with a PAHs detection device for the detection of PAHs.

5. The use of the hydrazone COF-based solid phase microextraction fiber in the detection of PAHs according to claim 4, characterized in that: The specific steps are as follows: the hydrazone COF-based solid phase microextraction fiber is placed above the test solution for extraction through headspace solid phase microextraction, and then inserted into the sampling port of the PAHs detection device for thermal desorption, and then analyzed and detected after desorption, wherein the extraction time is 20-45 min, the extraction temperature is 35-60°C, the stirring speed during the extraction process is 400-1200 rpm, the desorption time is 1-6 min, and the desorption temperature is 250-300°C.

Images