MOFs-chitosan composite solid-phase microextraction membrane, preparation method thereof and application of MOFs-chitosan composite solid-phase microextraction membrane in electronic cigarette analysis

Abstract

The invention relates to an MOFs-chitosan composite solid-phase micro-extraction membrane and a preparation method and application thereof in electronic cigarette analysis, the preparation method comprises the following steps: respectively dissolving PCN-250 and chitosan in a solvent to obtain a PCN-250 solution and a chitosan solution, stirring and mixing the two solutions, then carrying out ultrasonic dispersion, spin-coating and drying to obtain a coarse membrane, and preparing the MOFs-chitosan composite solid-phase micro-extraction membrane. And cross-linking the crude membrane with a cross-linking agent, and drying to obtain the membrane. According to the prepared composite matrix membrane, MOFs-and chitosan cooperate with each other, and precise recognition and efficient selective extraction of diacetyl and structural analogues thereof in the electronic cigarette are achieved through specific interaction. According to the composite membrane, the high specific surface area of MOFs is utilized, the adsorption capacity of the composite membrane on diacetyl and structural analogues thereof is large, rapid enrichment can be achieved, and the analysis sensitivity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic cigarette physical and chemical index detection technology, and in particular to a MOFs-chitosan composite solid phase microextraction membrane, a preparation method thereof, and application in electronic cigarette analysis. Background Art

[0002] Diacetyl and its structural analogs are common additives in e-cigarettes. They play a crucial role in the flavoring process of e-cigarette liquids, imparting unique flavors such as cream and caramel to meet the diverse taste demands of consumers. However, numerous studies have shown that long-term exposure to diacetyl and its structural analogs can cause serious harm to human health. For example, diacetyl and its structural analogs can cause bronchiolitis obliterans, an irreversible disease that severely affects lung function.

[0003] To protect the health rights of consumers, countries around the world have stepped up their regulation of e-cigarette products. Establishing strict standards and limits for the content of diacetyl and its structural analogs in e-cigarettes has become a key component of this regulation. This necessitates the development of precise and efficient analytical and testing technologies to accurately measure the levels of these substances in e-cigarettes and ensure compliance with relevant regulations. Sample extraction and enrichment are crucial pre-processing steps in the analysis and testing of diacetyl and its structural analogs in e-cigarettes, directly impacting the accuracy and reliability of subsequent test results.

[0004] Metal-organic frameworks (MOFs) and chitosan, two materials with unique properties, have garnered widespread attention in recent years. MOFs, with their high surface area, tunable pore structure, and abundant active sites, can efficiently adsorb specific compounds through various interactions with target molecules (such as hydrogen bonding, π-π stacking, and electrostatic interactions). Currently, traditional methods for pretreatment of e-cigarette samples face numerous limitations. On the one hand, traditional liquid-liquid extraction requires the use of large amounts of organic solvents, which not only pollutes the environment but also introduces impurities that interfere with analytical results. On the other hand, some conventional solid-phase extraction techniques have limited selectivity and enrichment efficiency when processing complex samples, making them difficult to accurately analyze trace components in e-cigarettes. For example, the extraction and purification method for synthetic cannabinoids from e-cigarette oils disclosed in CN118217668A utilizes traditional organic solvents or membrane filtration. This not only introduces organic solvents, reducing purity, but also reduces the purity of the sample obtained by membrane filtration alone, necessitating further purification.

[0005] At present, traditional sample extraction and enrichment methods are not practical in view of the regulatory requirements of the e-cigarette industry and the shortcomings of existing analytical detection technologies. It is urgent to develop an efficient, accurate, environmentally friendly and highly selective sample extraction and enrichment method. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a MOFs-chitosan composite solid-phase microextraction membrane, a preparation method thereof, and its application in electronic cigarette analysis. The composite matrix membrane prepared by the present invention enables MOFs and chitosan to work together, and through specific interactions, achieves accurate identification and efficient selective extraction of diacetyl and its structural analogues in electronic cigarettes.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a MOFs-chitosan composite solid phase microextraction membrane, the preparation method comprising: dissolving PCN-250 and chitosan in a solvent respectively to obtain a PCN-250 solution and a chitosan solution, stirring and mixing the two solutions and then ultrasonically dispersing them, spin coating and drying to obtain a crude membrane, cross-linking the crude membrane with a cross-linking agent and then drying to obtain the membrane.

[0009] In this invention, the active groups of chitosan interact with MOFs to form a stable composite material, while also enhancing the adsorption capacity for certain polar compounds. Combining MOFs and chitosan to form a composite solid-phase microextraction membrane promises to overcome the shortcomings of existing technologies. On the one hand, the high specific surface area and tunable pore structure of MOFs are utilized to enhance the adsorption capacity and selectivity for diacetyl and its structural analogs. On the other hand, the biocompatibility and active groups of chitosan enhance the affinity of the composite membrane with the sample, improving extraction efficiency and stability.

[0010] The MOFs material selected in the present invention is PCN-250. Compared with other MOFs materials, PCN-250 has good stability, excellent water vapor stability, high specific surface area and suitable pore size.

[0011] Preferably, the solvent comprises aqueous formic acid and / or aqueous acetic acid.

[0012] Preferably, the concentration of the solvent is 2%-5%, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0013] Preferably, the ratio of chitosan to solvent is 1 g: (30-50) mL. The (30-50) mL may be, for example, 30 mL, 35 mL, 40 mL, 45 mL or 50 mL.

[0014] Preferably, the ratio of PCN-250 to solvent is 1 g: (20-40) mL. The (20-40) mL may be, for example, 20 mL, 30 mL, or 40 mL.

[0015] Preferably, the volume ratio of the PCN-250 solution to the chitosan solution is 1:(1.2-1.5). The (1.2-1.5) can be, for example, 1.2, 1.3, 1.4 or 1.5.

[0016] In the present invention, it is found that the ratio of PCN-250 solution to chitosan solution has a great influence on the detection effect. Outside the above range, it will lead to incomplete combination of MOFs and chitosan, greatly affecting the extraction results and reducing the adsorption and extraction effects of the composite matrix membrane.

[0017] The stirring speed is 200-400 r / min, and the time is 8-16 hours. The 200-400 r / min can be, for example, 200 r / min, 300 r / min, or 400 r / min. The 8-16 hours can be, for example, 8 hours, 10 hours, 12 hours, 15 hours, or 16 hours.

[0018] Preferably, the ultrasonic dispersion time is 30-60 min, and the 30-60 min can be, for example, 30 min, 40 min, 50 min or 60 min.

[0019] Preferably, the spin coating drying time is 12-24 hours and the temperature is 20-30° C. The 12-24 hours can be, for example, 12 hours, 18 hours, 20 hours or 24 hours, etc. The 20-30° C. can be, for example, 20° C., 25° C. or 30° C., etc.

[0020] Preferably, the cross-linking agent comprises a 1-3 mol / L aqueous sulfuric acid solution, wherein the 1-3 mol / L solution may be, for example, 1 mol / L, 2 mol / L, or 3 mol / L.

[0021] In the present invention, sulfuric acid aqueous solution is used as a cross-linking agent, which can effectively improve the selectivity and separation performance of the membrane compared to traditional cross-linking agents such as glyoxal;

[0022] Preferably, the crosslinking time is 12-24 hours and the temperature is 20-30° C. The 12-24 hours may be, for example, 12 hours, 18 hours, 20 hours, or 24 hours, etc. The 20-30° C. may be, for example, 20° C., 25° C., or 30° C., etc.

[0023] Preferably, the preparation method of PCN-250 comprises:

[0024] (1) mixing a 5-nitroisophthalic acid solution, a sodium hydroxide aqueous solution, and zinc powder, heating the mixture, adjusting the pH value, filtering, and drying the mixture to obtain azobenzenetetracarboxylic acid;

[0025] (2) dissolving ferric nitrate nonahydrate and adding sodium acetate, mixing and reacting, collecting the precipitate after centrifugation, washing and drying to obtain Fe3O(CH3COO)6 iron clusters;

[0026] (3) Azobenzene tetracarboxylic acid, Fe3O(CH3COO)6 iron cluster, glacial acetic acid and N,N-dimethylformamide are mixed, allowed to stand for reaction and then filtered to obtain the product.

[0027] Preferably, the mass ratio of the 5-nitroisophthalic acid, sodium hydroxide, and zinc powder is 1 g:(0.2-0.6) g:(0.5-0.8) g. The (0.2-0.6) g may be, for example, 0.2, 0.3, 0.4, 0.5, or 0.6. The (0.5-0.8) g may be, for example, 0.5, 0.6, 0.7, or 0.8.

[0028] Preferably, the heating temperature is 85-90° C. and the heating time is 8-16 hours. The 85-90° C. may be, for example, 85° C. or 90° C., etc. The 8-16 hours may be, for example, 8 hours, 10 hours, 12 hours, 14 hours or 16 hours, etc.

[0029] Preferably, the pH value is 2-4, for example, 2, 3 or 4.

[0030] Preferably, the mass ratio of the ferric nitrate nonahydrate to sodium acetate is 1 g:(4-6) g. The (4-6) may be, for example, 4, 5, or 6.

[0031] Preferably, the mixing reaction time is 12-36 hours, and the temperature is 20-30° C. The 8-16 hours can be, for example, 8 hours, 10 hours, 12 hours, 14 hours, or 16 hours, etc. The 20-30° C. can be, for example, 20° C., 25° C., or 30° C., etc.

[0032] Preferably, the mass volume ratio of the azobenzenetetracarboxylic acid, Fe3O(CH3COO)6, and glacial acetic acid is 1g:(0.5-3)g:(100-300)μL:(100-300)mL. The (0.5-3)g can be, for example, 0.5g, 1g, 1.5g, 2g, 2.5g, or 3g. The (100-300)μL can be, for example, 100μL, 150μL, 200μL, 250μL, or 300μL. The (100-300)mL can be, for example, 100mL, 150mL, 200mL, 250mL, or 300mL.

[0033] Preferably, the static reaction temperature is 120°C-160°C, and the time is 8-16 hours. The 120°C-160°C can be, for example, 120°C, 130°C, 140°C, 150°C, or 160°C. The 8-16 hours can be, for example, 8 hours, 10 hours, 12 hours, 14 hours, 15 hours, or 16 hours.

[0034] In a second aspect, the present invention provides a MOFs-chitosan composite solid phase microextraction membrane prepared by the preparation method of the MOFs-chitosan composite solid phase microextraction membrane described in the first aspect.

[0035] In a third aspect, the present invention provides an application of the MOFs-chitosan composite solid phase microextraction membrane described in the second aspect in extracting diacetyl and its structural analogues in electronic cigarettes.

[0036] In a fourth aspect, the present invention provides a method for extracting diacetyl and its structural analogues in electronic cigarettes using the MOFs-chitosan composite solid phase microextraction membrane described in the second aspect, the method comprising: performing headspace extraction on the electronic cigarette sample using the MOFs-chitosan composite solid phase microextraction membrane, removing the composite solid phase microextraction membrane and adding a desorption solution for solvent desorption.

[0037] Preferably, the headspace extraction time is 1-3 hours, and the temperature is 20-60° C. The 1-3 hours may be, for example, 1 hour, 2 hours, or 3 hours, etc. The 20-30° C. may be, for example, 20° C., 30° C., 40° C., 50° C., or 60° C., etc.

[0038] Preferably, the desorption time is 20-60 min, for example, 20 min, 30 min, 40 min, 50 min or 60 min.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] The composite matrix membrane prepared by the present invention utilizes MOFs and chitosan to synergize, leveraging specific interactions to achieve precise identification and efficient selective extraction of diacetyl and its structural analogs in electronic cigarettes. This composite matrix membrane leverages the high specific surface area of MOFs, resulting in a large adsorption capacity for diacetyl and its structural analogs, enabling rapid enrichment and improving analytical sensitivity. The application of this composite matrix membrane in the extraction and enrichment of electronic cigarette samples, along with actual sample testing and analysis, provides technical support for the regulation and quality evaluation of electronic cigarettes and contributes to the improvement of relevant testing standards. Furthermore, compared to existing technologies, the preparation method of the present invention is simple to operate and more suitable for factory production. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The present invention is a schematic flow chart of a method for preparing a MOFs-chitosan composite solid phase microextraction membrane.

[0042] Figure 2 are SEM images of PCN-250 / chitosan film and PCN-250 powder.

[0043] Figure 3 is the XRD pattern of PCN-250 / chitosan film and PCN-250 powder. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0045] The materials and instruments used in the following examples are from:

[0046] Gas chromatography-mass spectrometry: GCMS-TQ8040 NX, Shimadzu;

[0047] Ultrasonic cleaning apparatus: Ningbo Xinzhi Biotechnology Co., Ltd.;

[0048] Electronic analytical balance: ME204E, Mettler Toledo;

[0049] Glass instruments: Chongqing Xinweier Glass Instrument Co., Ltd.;

[0050] 5-Nitroisophthalic acid, anhydrous ethanol, sodium hydroxide, ferric nitrate nonahydrate, sodium acetate, glacial acetic acid, N,N-dimethylformamide: analytical grade, Beijing Mairida Technology Co., Ltd.

[0051] Example 1

[0052] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0053] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 2.85 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 4.65 g of zinc powder was added and the mixture was reacted in a 90°C waterbath for 12 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 3 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 42.18 g of sodium acetate was added. The mixture was stirred for 10 minutes and then maintained at 25°C for 24 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0054] 1.0 g of H4ABTC ligand and 1.0 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 200 mL of DMF. 200 μL of glacial acetic acid was then added. Ultrasonication was performed to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 140°C for 12 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0055] Weigh 1.5g of chitosan into a 100mL beaker, add 45mL of 2% acetic acid solution, and sonicate at 25°C until completely dissolved. Weigh 1.0g of PCN-250 powder and add 20mL of 2% acetic acid solution. Ultrasonic dispersion is performed for 30 minutes. The PCN-250 solution and chitosan solution are mixed in a volume ratio of 1:1.3 and stirred at 25°C and 300 rpm for 12 hours. Ultrasonic dispersion is then performed for 30 minutes, and the mixture is allowed to stand to degas. The mixture is placed on a stainless steel tray and dried at 25°C for 12 hours to obtain a crude MOFs-chitosan composite solid-phase microextraction membrane. The crude membrane is then cross-linked in a 2mol / L sulfuric acid solution for 24 hours. The membrane is then rinsed with ultrapure water until neutral and dried at 30°C for 48 hours to obtain a MOFs-chitosan composite solid-phase microextraction membrane.

[0056] Accurately weigh 1.0g of e-cigarette oil and place it in a 20mL headspace bottle. Insert the syringe needle through the polytetrafluoroethylene-lined silicone rubber pad on the bottle cap. Let the membrane adhere naturally to the clean syringe needle. Tighten the bottle cap to seal the sample and adjust the syringe position so that the composite solid phase microextraction membrane is placed in the headspace position of the headspace bottle. Perform headspace extraction at 40°C for 2h. Take out the composite solid phase microextraction membrane and place it in a centrifuge tube. Add 1mL of methanol for desorption for 30min. After desorption, directly inject the sample for analysis. The specific operation process is as follows: Figure 1 shown.

[0057] Example 2

[0058] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0059] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 1.4 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 3.5 g of zinc powder was added and the mixture was reacted in an 85°C waterbath for 16 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 2 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 32 g of sodium acetate was then added. The mixture was stirred for 10 minutes and then maintained at 20°C for 36 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0060] 1.0 g of H4ABTC ligand and 0.5 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 100 mL of DMF. 100 μL of glacial acetic acid was then added. Ultrasonication was used to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 120°C for 8 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0061] Weigh 1.5g of chitosan into a 100mL beaker, add 60mL of 2% acetic acid solution, and sonicate at 25°C until completely dissolved. Weigh 1.0g of PCN-250 powder and add 30mL of 2% acetic acid solution. Ultrasonic dispersion is performed for 30 minutes. The PCN-250 solution and chitosan solution are mixed in a volume ratio of 1:1.2, stirred at 400 rpm at 25°C for 8 hours, ultrasonically dispersed for 60 minutes, and allowed to stand to degas. The mixture is placed on a stainless steel tray and dried at 20°C for 24 hours to obtain a crude MOFs-chitosan composite solid-phase microextraction membrane. The crude membrane is then cross-linked in 1mol / L sulfuric acid solution for 24 hours, rinsed with ultrapure water until neutral, and dried at 30°C for 48 hours to obtain a MOFs-chitosan composite solid-phase microextraction membrane.

[0062] Accurately weigh 1.0g of e-cigarette oil and place it in a 20mL headspace bottle. Insert the syringe needle through the polytetrafluoroethylene-lined silicone rubber pad on the bottle cap. Let the membrane adhere naturally to the clean syringe needle. Tighten the bottle cap to seal the sample and adjust the syringe position so that the composite solid phase microextraction membrane is placed in the headspace position of the headspace bottle. Perform headspace extraction at 40°C for 1h. Take out the composite solid phase microextraction membrane and place it in a centrifuge tube. Add 1mL of methanol for desorption for 30min. After desorption, directly inject the sample for analysis. The specific operation process is as follows: Figure 1 shown.

[0063] The only difference between this embodiment and embodiment 1 is that the headspace extraction time is adjusted to 1 hour, and the rest is the same as embodiment 1.

[0064] Example 3

[0065] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0066] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 4.2 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 5.6 g of zinc powder was added and the mixture was reacted in a 90°C waterbath for 12 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 4 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 48 g of sodium acetate was then added. The mixture was stirred for 10 minutes and then maintained at 30°C for 12 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0067] 1.0 g of H4ABTC ligand and 3 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 300 mL of DMF. 300 μL of glacial acetic acid was then added. Ultrasonication was performed to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 160°C for 8 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0068] Weigh 1.5g of chitosan into a 100mL beaker, add 75mL of 2% acetic acid solution, and sonicate at 25°C until completely dissolved. Weigh 1.0g of PCN-250 powder and add 40mL of 2% acetic acid solution. Ultrasonic dispersion is performed for 30 minutes. The PCN-250 solution and chitosan solution are mixed in a volume ratio of 1:1.5, stirred at 200 rpm at 25°C for 16 hours, ultrasonically dispersed for 30 minutes, and allowed to stand to degas. The mixture is placed on a stainless steel tray and dried at 30°C for 12 hours to obtain a crude MOFs-chitosan composite solid-phase microextraction membrane. The crude membrane is then cross-linked in 3mol / L sulfuric acid solution for 12 hours, rinsed with ultrapure water until neutral, and dried at 30°C for 48 hours to obtain a MOFs-chitosan composite solid-phase microextraction membrane.

[0069] Accurately weigh 1.0g of e-cigarette oil and place it in a 20mL headspace bottle. Insert the syringe needle through the polytetrafluoroethylene-lined silicone rubber pad on the bottle cap. Let the membrane adhere naturally to the clean syringe needle. Tighten the bottle cap to seal the sample and adjust the syringe position so that the composite solid phase microextraction membrane is placed in the headspace position of the headspace bottle. Perform headspace extraction at 40°C for 3h. Take out the composite solid phase microextraction membrane and place it in a centrifuge tube. Add 1mL of methanol for desorption for 30min. After desorption, directly inject the sample for analysis. The specific operation process is as follows: Figure 1 shown.

[0070] The only difference between this embodiment and embodiment 1 is that the headspace extraction time is adjusted to 3 hours, and the rest is the same as embodiment 1.

[0071] Example 4

[0072] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0073] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 2.85 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 4.65 g of zinc powder was added and the mixture was reacted in a 90°C waterbath for 12 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 3 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 42.18 g of sodium acetate was added. The mixture was stirred for 10 minutes and then maintained at 25°C for 24 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0074] 1.0 g of H4ABTC ligand and 1.0 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 200 mL of DMF. 200 μL of glacial acetic acid was then added. Ultrasonication was performed to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 140°C for 12 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0075] Weigh 1.5g of chitosan into a 100mL beaker, add 45mL of 2% acetic acid solution, and sonicate at 25°C until completely dissolved. Weigh 1.0g of PCN-250 powder and add 20mL of 2% acetic acid solution. Ultrasonic dispersion is performed for 30 minutes. The PCN-250 solution and chitosan solution are mixed in a volume ratio of 1:1.3, stirred at 300 rpm at 25°C for 12 hours, ultrasonically dispersed for 30 minutes, and allowed to stand to degas. The mixture is placed on a stainless steel tray and dried at 25°C for 12 hours to obtain a crude MOFs-chitosan composite solid-phase microextraction membrane. The crude membrane is then cross-linked in 2mol / L sulfuric acid solution for 24 hours, rinsed with ultrapure water until neutral, and dried at 30°C for 48 hours to obtain a MOFs-chitosan composite solid-phase microextraction membrane.

[0076] Accurately weigh 1.0g of e-cigarette oil and place it in a 20mL headspace bottle. Insert the syringe needle through the polytetrafluoroethylene-lined silicone rubber pad on the bottle cap. Let the membrane adhere naturally to the clean syringe needle. Tighten the bottle cap to seal the sample and adjust the syringe position so that the composite solid phase microextraction membrane is placed in the headspace position of the headspace bottle. Perform headspace extraction at 20°C for 2h. Take out the composite solid phase microextraction membrane and place it in a centrifuge tube. Add 1mL of methanol for desorption for 30min. After desorption, directly inject the sample for analysis. The specific operation process is as follows: Figure 1 shown.

[0077] The only difference between this embodiment and embodiment 1 is that the headspace extraction temperature is adjusted to 20° C., and the rest is the same as embodiment 1.

[0078] Example 5

[0079] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0080] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 2.85 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 4.65 g of zinc powder was added and the mixture was reacted in a 90°C waterbath for 12 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 3 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 42.18 g of sodium acetate was added. The mixture was stirred for 10 minutes and then maintained at 25°C for 24 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0081] 1.0 g of H4ABTC ligand and 1.0 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 200 mL of DMF. 200 μL of glacial acetic acid was then added. Ultrasonication was performed to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 140°C for 12 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0082] Weigh 1.5g of chitosan into a 100mL beaker, add 45mL of 2% acetic acid solution, and sonicate at 25°C until completely dissolved. Weigh 1.0g of PCN-250 powder and add 20mL of 2% acetic acid solution. Ultrasonic dispersion is performed for 30 minutes. The PCN-250 solution and chitosan solution are mixed in a volume ratio of 1:1.3, stirred at 300 rpm at 25°C for 12 hours, ultrasonically dispersed for 30 minutes, and allowed to stand to degas. The mixture is placed on a stainless steel tray and dried at 25°C for 12 hours to obtain a crude MOFs-chitosan composite solid-phase microextraction membrane. The crude membrane is then cross-linked in 2mol / L sulfuric acid solution for 24 hours, rinsed with ultrapure water until neutral, and dried at 30°C for 48 hours to obtain a MOFs-chitosan composite solid-phase microextraction membrane.

[0083] Accurately weigh 1.0g of e-cigarette oil and place it in a 20mL headspace bottle. Insert the syringe needle through the polytetrafluoroethylene-lined silicone rubber pad on the bottle cap. Let the membrane adhere naturally to the clean syringe needle. Tighten the bottle cap to seal the sample and adjust the syringe position so that the composite solid phase microextraction membrane is placed in the headspace position of the headspace bottle. Perform headspace extraction at 30°C for 2h. Take out the composite solid phase microextraction membrane and place it in a centrifuge tube. Add 1mL of methanol for desorption for 30min. After desorption, directly inject the sample for analysis. The specific operation process is as follows: Figure 1 shown.

[0084] The only difference between this embodiment and embodiment 1 is that the headspace extraction temperature is adjusted to 30° C., and the rest is the same as embodiment 1.

[0085] Example 6

[0086] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0087] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 2.85 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 4.65 g of zinc powder was added and the mixture was reacted in a 90°C waterbath for 12 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 3 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 42.18 g of sodium acetate was added. The mixture was stirred for 10 minutes and then maintained at 25°C for 24 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0088] 1.0 g of H4ABTC ligand and 1.0 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 200 mL of DMF. 200 μL of glacial acetic acid was then added. Ultrasonication was performed to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 140°C for 12 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0089] Weigh 1.5g of chitosan into a 100mL beaker, add 45mL of 2% acetic acid solution, and sonicate at 25°C until completely dissolved. Weigh 1.0g of PCN-250 powder and add 20mL of 2% acetic acid solution. Ultrasonic dispersion is performed for 30 minutes. The PCN-250 solution and chitosan solution are mixed in a volume ratio of 1:1.3, stirred at 300 rpm at 25°C for 12 hours, ultrasonically dispersed for 30 minutes, and allowed to stand to degas. The mixture is placed on a stainless steel tray and dried at 25°C for 12 hours to obtain a crude MOFs-chitosan composite solid-phase microextraction membrane. The crude membrane is then cross-linked in 2mol / L sulfuric acid solution for 24 hours, rinsed with ultrapure water until neutral, and dried at 30°C for 48 hours to obtain a MOFs-chitosan composite solid-phase microextraction membrane.

[0090] Accurately weigh 1.0g of e-cigarette oil and place it in a 20mL headspace bottle. Insert the syringe needle through the polytetrafluoroethylene-lined silicone rubber pad on the bottle cap. Let the membrane adhere naturally to the clean syringe needle. Tighten the bottle cap to seal the sample and adjust the syringe position so that the composite solid phase microextraction membrane is placed in the headspace position of the headspace bottle. Perform headspace extraction at 50°C for 2h. Take out the composite solid phase microextraction membrane and place it in a centrifuge tube. Add 1mL of methanol for desorption for 30min. After desorption, directly inject the sample for analysis. The specific operation process is as follows: Figure 1 shown.

[0091] The only difference between this embodiment and embodiment 1 is that the headspace extraction temperature is adjusted to 50° C., and the rest is the same as embodiment 1.

[0092] Example 7

[0093] This example prepares MOFs-chitosan composite solid phase microextraction membrane

[0094] 7.0 g of 5-nitroisophthalic acid was weighed and placed in a round-bottom flask. 180 mL of anhydrous ethanol was added to dissolve it. 2.85 g of NaOH was dissolved in 75 mL of ultrapure water and added to the round-bottom flask. 4.65 g of zinc powder was added and the mixture was reacted in a 90°C waterbath for 12 hours. The zinc powder was removed by filtration under reduced pressure. The filtrate was adjusted to pH 3 with 3 mol / L hydrochloric acid. After filtration, a yellow solid was obtained. Azobenzenetetracarboxylic acid was obtained by drying at 40°C. 8.0 g of Fe(NO3)3·9H2O was dissolved in 70 mL of ultrapure water. 42.18 g of sodium acetate was added. The mixture was stirred for 10 minutes and then maintained at 25°C for 24 hours. The precipitate was collected by centrifuge, washed with ethanol, and dried at 40°C to obtain the precursor Fe3O(CH3COO)6 iron cluster.

[0095] 1.0 g of H4ABTC ligand and 1.0 g of Fe3O(CH3COO)6 iron cluster were weighed and dissolved in a flask containing 200 mL of DMF. 200 μL of glacial acetic acid was then added. Ultrasonication was performed to evenly disperse the solids in the DMF solution. The mixture was placed in a vacuum drying oven at 140°C for 12 hours. After cooling to room temperature, the mixture was filtered to obtain dark brown crystalline PCN-250 material.

[0096] Weigh 1.5g of chitosan in a 100mL beaker, add 45mL of 2% acetic acid aqueous solution, and stir at 25℃ after ultrasonication until completely dissolved. Weigh 1.0g of PCN-250 powder and add 20mL of 2% acetic acid aqueous solution, and ultrasonically disperse for 30min. Take PCN-250 solution and chitosan solution in a volume ratio of 1:1.3, stir at 25℃ and 300r / min for 12h, ultrasonically disperse for 30min, and let stand to degas. Place the mixed solution on a stainless steel tray and dry at 25℃ for 12h to obtain a MOFs-chitosan composite solid phase microextraction crude membrane. Then, place the crude membrane in a 2mol / L sulfuric acid solution for cross-linking for 24h, then rinse with ultrapure water until neutral, and dry at 30℃ for 48h to obtain a MOFs-chitosan composite solid phase microextraction membrane. The specific operation process is as follows Figure 1 shown.

[0097] The only difference between this embodiment and embodiment 1 is that the headspace extraction temperature is adjusted to 60° C., and the rest is the same as embodiment 1.

[0098] Comparative Example 1

[0099] Accurately weigh 1.0 g of e-cigarette liquid and place it in a 25 mL centrifuge tube. Add 20 mL of methanol, seal the tube, and place it in a vortex shaker. Ultrasonic extraction was performed for 60 min. After standing, the upper organic phase was filtered and centrifuged to obtain the supernatant for sampling and analysis.

[0100] The difference between this comparative example and Example 1 is that the thin film solid phase microextraction method is not used, and the traditional liquid-liquid extraction method is selected to compare the difference in extraction efficiency.

[0101] Test Example 1

[0102] This test example extracts diacetyl and its structural analogues from e-cigarette oil samples.

[0103] (1) Material characterization

[0104] In this test example, the MOFs-chitosan composite solid phase microextraction membrane prepared in Example 1 was observed by electron microscopy. The specific results are as follows: Figure 2 As shown in Figures A, B, C and D, it can be found that PCN-250 particles can be tightly combined with chitosan, and agglomeration occurs, but the surface of the composite film is smooth and tight without obvious defects. Figure 3Figure 3 is the XRD diagram of PCN-250 and its film-forming structure. It can be seen from the figure that there are obvious diffraction peaks at positions such as 9.5°13.5°, 16.5°, 18.5°, 20.5°, and 23.5°, but there are no obvious diffraction peaks after film formation, indicating that the characteristic peaks of the MOFs film are covered by the influence of the chitosan substrate, further confirming that PCN-250 can be tightly combined with chitosan.

[0105] (2) Performance testing

[0106] 1.0g of e-cigarette liquid was placed in a 20mL headspace vial. The syringe needle was inserted through the Teflon-lined silicone rubber pad on the vial cap. The MOFs-chitosan composite solid-phase microextraction membranes prepared in the above examples and comparative examples were naturally adhered to the clean syringe needles. The vial cap was tightened to seal the sample, and the syringe position was adjusted to place the MOFs-chitosan composite solid-phase microextraction membrane in the headspace of the vial. Headspace extraction was performed at room temperature for 2 hours. The MOFs-chitosan composite solid-phase microextraction membrane was removed and placed in a centrifuge tube. 1mL of methanol was added for desorption for 20 minutes. After desorption, the sample was directly analyzed by GC-QTOF-MS.

[0107] The following testing procedures were used: transfer line temperature: 240°C; column flow rate: 2.15 mL / min; purge flow rate: 1.0 mL / min; split ratio: 20:1; injection volume: 1.5 μL; chromatographic mass spectrometer interface temperature: 240°C; ion source temperature: 200°C; acquisition mode: Q3SCAN + SIM mode. A DA-WAX column (30 m × 0.25 mm × 0.25 μm) was used. The column temperature program was: initial temperature of 40°C for 2 min, then increased at 5°C / min to 100°C and held for 2 min, then increased at 30°C / min to 240°C and held for 2 min. Characteristic ion information for the five compounds is shown in Table 1.

[0108] Table 1

[0109] serial number Compound Quantitative ion (m / z) Qualifier ion (m / z) 1 Diacetyl 86 43，86 2 Levulinyl 100 43，57，100 3 Acetobutyryl 71 43，71，114 4 Acetylvaleryl 85 57，85，128 5 Acetoin 88 43，45，88

[0110] The specific test results are shown in Table 2:

[0111] Table 2

[0112]

[0113] The test results show that:

[0114] (1) It can be seen from Examples 1 to 2-7 that the composite matrix membrane prepared by the present invention enables MOFs and chitosan to cooperate with each other and achieve accurate recognition and efficient selective extraction of diacetyl in electronic cigarettes through specific interaction.

[0115] (2) By comparing Example 1 with Examples 2-3, it can be seen that changing the headspace extraction time will affect the extraction efficiency of diacetyl. The shorter or longer the extraction time, the lower the extraction efficiency.

[0116] (3) By comparing Example 1 with Examples 4-7, it can be seen that changing the headspace extraction temperature will affect the extraction efficiency of diacetyl. The higher or lower the temperature, the lower the extraction efficiency.

[0117] (4) By comparing Example 1 with Comparative Example 1, it can be seen that the extraction efficiency of diacetyl can be significantly improved by using the MOFs-chitosan composite solid phase microextraction membrane for extraction.

[0118] Test Example 2

[0119] This test case performs stability testing

[0120] E-cigarette samples: The 35 national standard e-cigarettes on the market are numbered S1-S35, among which S1-S12 come from brand A, S13-S22 come from brand B, S23-S27 come from brand C, S28-S29 come from brand D, S30-S31 come from brand D, and S32-S35 come from brand F.

[0121] Six portions of S1-S35 e-cigarette liquid (1.0 g) were precisely weighed and placed into a 20 mL headspace vial. A syringe needle was inserted through the Teflon-lined silicone rubber pad on the vial cap. The MOFs-chitosan composite solid-phase microextraction membrane was naturally adhered to the clean syringe needle. The vial cap was tightened to seal the sample, and the syringe was adjusted to position the MOFs-chitosan composite solid-phase microextraction membrane in the headspace of the vial. Headspace extraction was performed at room temperature for 2 hours. The MOFs-chitosan composite solid-phase microextraction membrane was removed and placed in a centrifuge tube. Desorption was carried out for 20 minutes with the addition of 1 mL of methanol. The desorbed solution was then directly injected and analyzed by GC-QTOF-MS. The analysis conditions were as follows: transfer line temperature: 240°C; column flow rate: 2.15 mL / min; purge flow rate: 1.0 mL / min; split ratio: 20:1; injection volume: 1.5 μL; chromatographic mass spectrometry interface temperature: 240°C; ion source temperature: 200°C; acquisition mode: Q3SCAN+SIM mode.

[0122] A DA-WAX (30 m × 0.25 mm × 0.25 μm) column was used, and the column temperature program was as follows: initial column temperature was 40 °C for 2 min, then increased to 100 °C at a rate of 5 °C / min and continued for 2 min, then increased to 240 °C at a rate of 30 °C / min and continued for 2 min. The characteristic ion information of the five compounds is shown in Table 3.

[0123] Table 3

[0124] serial number Compound Quantitative ion (m / z) Qualifier ion (m / z) 1 Diacetyl 86 43，86 2 Levulinyl 100 43，57，100 3 Acetobutyryl 71 43，71，114 4 Acetylvaleryl 85 57，85，128 5 Acetoin 88 43，45，88

[0125] The specific test results are shown in Table 4. Diacetyl and acetylvaleryl were detected in 43 e-liquid samples, with contents ranging from 7.448-19.426 μg / g and 0-0.629 μg / g, respectively. However, acetylpropionyl, acetobutyryl and acetoin were not detected. This is consistent with the test results of the liquid-liquid extraction method, and it is speculated that the samples basically do not contain these three components.

[0126] Table 4

[0127]

[0128]

[0129] In summary, the composite matrix membrane prepared by the present invention utilizes MOFs and chitosan to synergize, achieving precise identification and efficient selective extraction of diacetyl from electronic cigarettes through specific interactions. This composite matrix membrane utilizes the high specific surface area of MOFs, resulting in a large adsorption capacity for diacetyl, enabling rapid enrichment and improving analytical sensitivity.

[0130] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a MOFs-chitosan composite solid phase microextraction membrane, characterized in that: The preparation method comprises: dissolving PCN-250 and chitosan in a solvent respectively to obtain a PCN-250 solution and a chitosan solution, stirring and mixing the two solutions and then performing ultrasonic dispersion, spin coating and drying to obtain a crude membrane, and cross-linking and drying the crude membrane to obtain a composite solid phase microextraction membrane.

2. The method for preparing the MOFs-chitosan composite solid phase microextraction membrane according to claim 1, characterized in that: The solvent includes an aqueous formic acid solution and / or an aqueous acetic acid solution; Preferably, the concentration of the solvent is 2%-5%.

3. The method for preparing the MOFs-chitosan composite solid phase microextraction membrane according to claim 1 or 2, characterized in that: The ratio of chitosan to solvent is 1 g: (30-50) mL; Preferably, the ratio of PCN-250 to solvent is 1 g: (20-40) mL; Preferably, the volume ratio of the PCN-250 solution to the chitosan solution is 1:(1.2-1.5).

4. The method for preparing a MOFs-chitosan composite solid phase microextraction membrane according to any one of claims 1 to 3, characterized in that: The stirring speed is 200-400 r / min and the time is 8-16 h; Preferably, the ultrasonic dispersion time is 30-60 min; Preferably, the spin coating drying time is 12-24 hours and the temperature is 20-30°C; Preferably, the cross-linking agent used for the cross-linking comprises a 1-3 mol / L sulfuric acid aqueous solution; Preferably, the cross-linking time is 12-24 hours and the temperature is 20-30°C.

5. The method for preparing a MOFs-chitosan composite solid phase microextraction membrane according to any one of claims 1 to 4, characterized in that: The preparation method of PCN-250 comprises: (1) mixing a 5-nitroisophthalic acid solution, a sodium hydroxide aqueous solution, and zinc powder, heating the mixture, adjusting the pH value, filtering, and drying the mixture to obtain azobenzenetetracarboxylic acid; (2) dissolving ferric nitrate nonahydrate and adding sodium acetate, mixing and reacting, collecting the precipitate after centrifugation, washing and drying to obtain Fe3O(CH3COO)6 iron clusters; (3) Azobenzene tetracarboxylic acid, Fe3O(CH3COO)6 iron cluster, glacial acetic acid and N,N-dimethylformamide are mixed, allowed to stand for reaction and then filtered to obtain the product.

6. The method for preparing the MOFs-chitosan composite solid phase microextraction membrane according to claim 5, characterized in that: The mass ratio of the 5-nitroisophthalic acid, sodium hydroxide and zinc powder is 1g:(0.2-0.6)g:(0.5-0.8)g; Preferably, the heating temperature is 85-90°C and the heating time is 8-16h; Preferably, the pH value is 2-4; Preferably, the mass ratio of the ferric nitrate nonahydrate to sodium acetate is 1 g:(4-6) g; Preferably, the mixing reaction time is 12-36 hours and the temperature is 20-30°C; Preferably, the mass volume ratio of the azobenzenetetracarboxylic acid, Fe3O(CH3COO)6, glacial acetic acid and N,N-dimethylformamide is 1g:(0.5-3)g:(100-300)μL:(100-300)mL; Preferably, the temperature of the static reaction is 120° C.-160° C., and the time is 8-16 hours. 7 . A MOFs-chitosan composite solid phase microextraction membrane prepared by the method for preparing a MOFs-chitosan composite solid phase microextraction membrane according to any one of claims 1 to 6 .

8. Use of the MOFs-chitosan composite solid phase microextraction membrane according to claim 7 in extracting diacetyl and its structural analogues in electronic cigarettes.

9. A method for extracting diacetyl and its structural analogs in electronic cigarettes using the MOFs-chitosan composite solid phase microextraction membrane according to claim 7, characterized in that: The method comprises: performing headspace extraction on an electronic cigarette sample using the MOFs-chitosan composite solid phase microextraction membrane, taking out the composite solid phase microextraction membrane, adding a desorption solution into the solvent for desorption.

10. The method for extracting diacetyl and its structural analogues in electronic cigarettes using a MOFs-chitosan composite solid phase microextraction membrane according to claim 9, characterized in that: The headspace extraction time is 1-3h and the temperature is 20-60°C; Preferably, the desorption time is 20-60 min.

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