Preparation method and application of carboxyl-functionalized MON-coated ZIF-8-NH2 solid-phase microextraction material

Abstract

The invention discloses a preparation method and application of a carboxyl functionalized MON (at) ZIF-8-NH2 solid phase microextraction material. The preparation method comprises the following steps: taking ZIF-8-NH2 as an inner core and MON-2COOH as a shell to obtain a carboxyl-functionalized MON-coated ZIF-8-NH2 material, then fixing the carboxyl-functionalized MON-coated ZIF-8-NH2 material on a substrate by adopting a physical coating technology to obtain a solid-phase micro-extraction coating fiber based on carboxyl-functionalized MON-coated ZIF-8-NH2, and using the extraction fiber to measure hydroxyl polycyclic aromatic hydrocarbon in urine. The solid-phase micro-extraction coating fiber disclosed by the invention is thinner in coating, better in extraction effect, longer in service life and higher in stability. The method can be used for extracting various hydroxyl polycyclic aromatic hydrocarbons in urine at the same time by being combined with liquid chromatography-mass spectrometry, and has good stability, meanwhile, the determination method has excellent accuracy, and the recovery rate and the detection limit meet the detection requirements of trace analysis.

Description

Technical Field

[0001] This invention relates to a method for preparing solid-phase microextraction materials and their applications, and more particularly to a method for preparing carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction materials and their applications. Background Technology

[0002] Polycyclic aromatic hydrocarbons (PAHs) and their derivatives are a class of persistent organic pollutants of significant importance. PAHs are hydrocarbon compounds containing two or more benzene rings in their molecular structure. PAHs possess teratogenic, carcinogenic, and mutagenic properties. Studies have confirmed that PAH exposure can damage the central nervous system in animals, disrupt lymphocyte micronucleus rates, affect liver function, and impair DNA repair capabilities. Furthermore, PAHs have endocrine disrupting effects, impacting the function of the reproductive endocrine system and leading to genetic damage. PAHs can enter the human body through respiration, digestion, and skin. In the body, under the action of cytochrome P450 enzymes, PAHs are converted into hydroxy polycyclic aromatic hydrocarbons (OH-PAHs). Subsequently, OH-PAHs are excreted in urine under the action of substances such as glucuronic acid and glutathione. Among these metabolic transformation products, hydroxy polycyclic aromatic hydrocarbons (PAHs) serve as key biomarkers, effectively reflecting the degree of an individual's recent exposure to PAHs. Therefore, they are widely used in environmental exposure assessment and occupational health monitoring as important indicators. Consequently, developing a sensitive and precise quantitative analytical method for hydroxy polycyclic aromatic hydrocarbons in urine is of paramount importance for assessing the exposure risk of parent compounds to human health.

[0003] Due to the low concentration of OH-PAHs in urine and the complex composition of the urine matrix, it is crucial to employ suitable and efficient pretreatment methods to pretreat target compounds before actual sample analysis to eliminate potential interferences and improve detection sensitivity. Currently, traditional pretreatment techniques such as liquid-liquid extraction and solid-phase extraction, while simple to operate, have many drawbacks, such as long processing time, large sample and organic solvent consumption, and serious environmental pollution caused by the volatility of extractants. Therefore, establishing new sample pretreatment methods to overcome the limitations of existing techniques for detecting trace PAHs in urine is of great significance. Solid-phase microextraction (SPME) is a sample pretreatment technique that integrates sampling, extraction, pre-enrichment, and injection, offering significant advantages such as ease of operation, high sensitivity, rapid extraction, almost no need for organic solvents, environmental friendliness, and good reproducibility. In 1993, Supelco in the United States pioneered its commercialization. However, commercially available SPME fibers suffer from drawbacks such as easy damage, limited variety, high cost, and poor specificity.

[0004] Therefore, developing new SPME fibers with excellent extraction performance, good selectivity, and good stability and durability is urgent and necessary for promoting the development of environmental health analysis and testing technology. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for preparing a carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material with excellent extraction performance, good selectivity, and good stability and durability; another purpose of this invention is to provide the application of the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material obtained by the above method in the extraction of hydroxy polycyclic aromatic hydrocarbons in urine.

[0006] Technical solution: The preparation method of the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material of the present invention includes the following steps:

[0007] (1) Place ZIF-8-NH2 powder in a mixed solvent of toluene and triethylamine, and add copper iodide and palladium dichloride of bis(triphenylphosphine) in sequence, and react under heating and stirring conditions;

[0008] (2) Add 2,5-dibromoterephthalic acid and tetra(4-ethynylphenyl)methane, and continue heating and stirring; after the reaction is completed, centrifuge, wash and dry the mixture to obtain a shell-core structure carboxyl functionalized MON@ZIF-8-NH2 solid phase microextraction material with ZIF-8-NH2 as the core and MONs-2COOH as the shell.

[0009] The mass ratios of ZIF-8-NH2, palladium dichloride of bis(triphenylphosphine), copper iodide, and 2,5-dibromoterephthalic acid to tetrakis(4-ethynylphenyl)methane are 7.5:1~10:1, 0.25:1~0.35:1, 2:1~2.5:1, and 1.5~1.6:1, respectively. Further, 150~200 mg of ZIF-8-NH2, 5~7 mg of palladium dichloride of bis(triphenylphosphine), 40~50 mg of copper iodide, 31.1 mg (0.096 mmol) of 2,5-dibromoterephthalic acid, and 20 mg (0.048 mmol) of tetrakis(4-ethynylphenyl)methane are used.

[0010] In step (1), the volume ratio of the toluene and triethylamine mixture is 2:1 to 3:1; an appropriate amount of ZIF-8-NH2 material is placed in the mixed solvent of toluene and triethylamine and ultrasonically treated until it is completely dissolved; the ultrasonic time is 10-15 min.

[0011] In step (1), the heating temperature is 80~100 ℃, the heating time is 0.5~2 h, and the stirring speed is 600-750 rpm; then 2,5-dibromoterephthalic acid and tetra(4-ethynylphenyl)methane are added and heated for 3-5 h under the same conditions.

[0012] In step (2), the mixture is centrifuged at 8000-10000 rpm for 4-6 min, washed with methanol 3-4 times, and the resulting solid is dried in an oven at 60-80℃.

[0013] The above method was used to extract hydroxy polycyclic aromatic hydrocarbons from urine.

[0014] In this process, the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material is fixed on a support substrate using a physical coating method to obtain a solid-phase microextraction coated fiber. The solid-phase microextraction coated fiber is then immersed in a urine sample after enzymatic hydrolysis and extracted by stirring.

[0015] The specific extraction procedure is as follows: take the enzymatically hydrolyzed urine sample, insert the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction coated fiber into the urine sample, stir at a constant speed of 600-800 rpm at an extraction temperature of 50-60 ℃, and extract for 30-40 min.

[0016] The preparation process of the solid-phase microextraction (SPI) coated fiber is as follows: A clean stainless steel wire is etched at one end with a 40% hydrofluoric acid solution for 50 minutes to form a rough surface. The etched stainless steel wire is then washed with ultrapure water and dried in air. 0.4-0.6 g of silicone adhesive is placed in a centrifuge tube, diluted with 2.0-3.0 mL of n-hexane, and sonicated until homogeneous. The diluted silicone adhesive solution is then coated onto the etched stainless steel wire, which is then inserted into carboxyl-functionalized MON@ZIF-8-NH2 SPI material powder. The process is repeated 2-3 times to obtain a coating with a length of 1.5-3.0 cm and a thickness of approximately 40-50 μm. Finally, the coating is dried in an oven at 60℃ for 18-24 h. The supporting substrate can also be quartz.

[0017] After extraction, the coated fiber is placed in a mixed solution of methanol and water for static analysis; the mass ratio of methanol to water is 2:1 to 3:1; the analysis temperature is 25 to 30 ℃, and the analysis time is 8 to 10 h.

[0018] The specific process for enzymatic hydrolysis of urine samples is as follows: Add 10-15 μL of β-glucuronidase to 5-10 mL of urine sample, then add 1-3 mL of acetate-sodium acetate buffer solution to adjust the pH to 5-6, and heat in a water bath at 30-40 ℃ for 3-5 h. Centrifuge the hydrolyzed urine sample at 4000-5000 rpm for 5-15 min, and store the supernatant at 4 ℃ for later use.

[0019] Specifically, before adding β-glucuronidase, 5-10 mL of urine sample supernatant is placed in a centrifuge tube, and mixed standards of different concentrations are added. The mixed standards are mixed solutions containing at least one contaminant selected from 2-hydroxynaphthalene, 2-hydroxy-9-fluorenone, 2-hydroxyphenanthrene, 9-hydroxyphenanthrene, 4-hydroxyphenanthrene, 1,8-dihydroxyanthraquinone, and 1-hydroxypyrene. The concentration range of the mixed standards is 0.2-40 μg / L.

[0020] In this invention, the solid-phase microextraction (SPME) coated fiber is routinely stored inside a hollow fiber protective sleeve to prevent contamination or damage to the coating. During extraction, the coated fiber is pushed out of the protective sleeve, allowing it to directly contact the liquid sample for extraction. Subsequently, the coated fiber is placed in a methanol-water mixture for static elution, allowing the target substances adsorbed on the coating to be released into the solution for subsequent detection. This invention uses liquid chromatography-mass spectrometry (LC-MS) to determine hydroxyl polycyclic aromatic hydrocarbons (PAHs) in urine samples. The LC-MS method uses a 2.1 mm × 100 mm, 1.8 μm Agilent Zorbax Eclipse Plus C18 column, with pure water and methanol as the mobile phase; a flow rate of 0.2-0.3 mL / min; a run time of 13 min; gradient elution; and an electrospray ionization source in negative ion mode.

[0021] Invention Principle: This invention leverages the structural tunability and synergistic effect of microporous organic network materials and composite components to construct a carboxyl-functionalized shell-core structure MON@ZIF-8 material through multi-dimensional design and regulation, achieving highly efficient and selective adsorption and extraction of hydroxyl polycyclic aromatic hydrocarbons (OH-PAHs) in urine. Using MON, with its rigid planar structure, π-conjugated system, and porous characteristics, as a framework, carboxyl active functional groups are introduced. The carboxyl groups on the material surface possess both hydrogen bond acceptor and donor properties, forming a stable hydrogen bond network with the -OH groups of OH-PAHs. This network exhibits stronger interactions than van der Waals forces, enabling selective binding of target analytes from complex urine matrices. Furthermore, the amino groups modified on ZIF-8 and the carboxyl groups on MON can undergo condensation, enhancing material stability. Molecular size-selective sieving is achieved through the structural complementarity of MON and ZIF-8. The micropores of ZIF-8 screen small molecule targets and block interference from large molecules through size exclusion effects; the mesoporous and hollow structure of MON, combined with the three-dimensional fibrous network, forms highly efficient mass transfer channels, combining 1518 m... 2 The high specific surface area of ​​ / g simultaneously enhances adsorption selectivity and capacity. Specific hydrogen bonding is the core driving force for precise target analyte capture. The combination of hierarchical porous structure and the synergistic effect of active functional groups significantly improves the selectivity, sensitivity, and overall performance of solid-phase microextraction.

[0022] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0023] (1) The MON@ZIF-8-NH2 solid phase microextraction coating fiber prepared by the present invention is thinner, has better extraction effect, longer service life and higher stability. It can simultaneously extract multiple hydroxy polycyclic aromatic hydrocarbons in urine by coupling with liquid chromatography-mass spectrometry, and has good stability. At the same time, the determination method has excellent accuracy, recovery rate and detection limit meet the detection requirements of trace analysis.

[0024] (2) This invention prepares carboxyl-functionalized MON@ZIF-8-NH2 and coats it onto the surface of a stainless steel wire substrate to form a coating. This coating is then used as the extraction head for solid-phase microextraction to extract hydroxyl polycyclic aromatic hydrocarbons (HPAs) from environmental urine samples. By combining this with liquid chromatography-mass spectrometry (LC-MS), it can simultaneously detect HPAs in environmental urine samples with different properties, exhibiting a low detection limit, a wide linear range, and good stability in determining multiple HPAs in environmental urine samples. Furthermore, this method has excellent accuracy. Therefore, this invention provides a method for simultaneously determining multiple HPAs in environmental urine samples with a low detection limit and high precision. Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation method of the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction coated fiber of the present invention;

[0026] Figure 2 Scanning electron microscope images: ZIF-8 (a), ZIF-8-NH2 (b), MON (c), ZIF-8@MON (d), ZIF-8-NH2@MON-2COOH (e), ZIF-8-NH2@MON-2COOH (f);

[0027] Figure 3 The energy spectrum of ZIF-8-NH2@MON-2COOH solid-phase microextraction fiber;

[0028] Figure 4 Infrared chromatograms of five materials: ZIF-8, MON, ZIF-8-NH2, ZIF-8@MON, and ZIF-8-NH2@MON-2COOH;

[0029] Figure 5 The BET characterization diagram of ZIF-8-NH2@MON-2COOH;

[0030] Figure 6 The cumulative pore volume characterization diagram of ZIF-8-NH2@MON-2COOH;

[0031] Figure 7 Contact angle characterization diagrams: ZIF-8 (a), ZIF-8-NH2 (b), MON (c), ZIF-8@MON (d), ZIF-8-NH2@MON-2COOH (e);

[0032] Figure 8 A comparison of the extraction effects of five materials—ZIF-8, ZIF-8-NH2, ZIF-8@MON, MON, and ZIF-8-NH2@MON-2COOH—on seven hydroxyl polycyclic aromatic hydrocarbons;

[0033] Figure 9 A comparison of the extraction effects of different solvent ratios on seven hydroxyl polycyclic aromatic hydrocarbon pollutants;

[0034] Figure 10 The response surface methodology results for the optimization of four factors in the extraction and desorption process of core-shell carboxyl-functionalized ZIF-8@MON-2COOH fibers based on Box-Behnken design experiments are as follows: extraction time / extraction temperature (a); extraction time / desorption time (b); extraction temperature / desorption time (c).

[0035] Figure 11 Chromatograms of seven hydroxy polycyclic aromatic hydrocarbons (HPAs): 2-hydroxynaphthalene-D8, 2-hydroxynaphthalene, hydroxyphenanthrene, 2-hydroxy-9-fluorenone, 1-hydroxypyrene, and 1,8-dihydroxyanthraquinone.

[0036] Figure 12 This study compares the extraction efficiency of ZIF-8-NH2@MON-2COOH fiber with that of three commercial fibers for seven hydroxyl polycyclic aromatic hydrocarbon pollutants. Detailed Implementation

[0037] The present invention will now be described in further detail.

[0038] Example 1

[0039] like Figure 1 As shown, a method for preparing carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction coated fibers includes the following steps:

[0040] Step 1: Prepare carboxyl-functionalized MON@ZIF-8-NH2 coating material.

[0041] In a 100 mL round-bottom flask, 10 mL of triethylamine and 20 mL of toluene were mixed. Then, 50 mg of copper iodide and 6.8 mg of palladium dichloride bis(triphenylphosphine) chloride were added sequentially. After sonication at room temperature for 15 min, the mixture was heated and stirred at 90 °C and 700 rpm for 1 h. Subsequently, 31.1 mg of 2,5-dibromoterephthalic acid and 20 mg of tetra(4-ethynylphenyl)methane were rapidly added, and the mixture was heated and stirred under the same conditions for another 4 h. After the reaction was complete, the mixture was cooled to room temperature, centrifuged at 8000 rpm for 5 min, and the precipitate was washed three times with methanol. Finally, the product was dried overnight in an oven to obtain the carboxyl-functionalized MON@ZIF-8-NH2 material.

[0042] Step 2: Prepare solid-phase microextraction coated fibers.

[0043] Stainless steel wire was used as the substrate for preparing solid-phase microextraction (SPE) fibers. The stainless steel wire was ultrasonically cleaned with methanol and ultrapure water for 10 min each time, then dried in a 60 ℃ oven. One end of the clean stainless steel wire was etched with a 40% hydrofluoric acid solution for 50 min to create a rough surface. The etched stainless steel wire was then cleaned with ultrapure water and air-dried. 0.4 g of silicone adhesive was placed in a centrifuge tube, diluted with 2.0 mL of n-hexane, and ultrasonicated until homogeneous. The diluted silicone adhesive solution was coated onto the etched stainless steel wire, which was then inserted into the prepared carboxyl-functionalized MON@ZIF-8-NH2 powder. The process was repeated three times to obtain a solid-phase microextraction coated fiber with a thickness of approximately 50 μm. Finally, the fiber was dried in a 60 ℃ oven for 24 h.

[0044] Solid-phase microextraction (SPME) coated fibers are routinely stored inside hollow fiber sheaths to prevent contamination or damage to the coating. When used for extraction, the coated fibers are extended from the sheaths to allow direct contact with the liquid sample for extraction.

[0045] Comparative Example 1

[0046] ZIF-8 material was prepared. 1.947 g of 2-methylimidazole and 0.879 g of zinc nitrate hexahydrate were weighed and dissolved in 60 mL of methanol. The mixture was stirred at 700 rpm for 1 h at room temperature. After the reaction was complete, the mixture was cooled to room temperature and centrifuged at 8000 rpm for 5 min. The precipitate was washed three times with methanol, and finally, the product was dried in an oven overnight to obtain ZIF-8 material.

[0047] Comparative Example 2

[0048] ZIF-8-NH2 material was prepared. 0.744 g of zinc nitrate hexahydrate was weighed and dissolved in 25 mL of N,N-dimethylformamide, and stirred to obtain a homogeneous solution A. Separately, 0.135 g of 2-aminobenzimidazole, 0.739 g of 2-methylimidazole, and 0.05 g of sodium formate were weighed and dissolved in 25 mL of deionized water. The solutions were ultrasonically dispersed at 20–25 °C for 15 min to obtain a homogeneous solution B. Solution B was heated at 70 °C and 700 rpm for 2 h. After the reaction was complete, solution B was allowed to stand at room temperature for 5 h, and immediately solution A was added to solution B. The mixture was magnetically stirred at 700 rpm for 30 min. After naturally cooling to room temperature, the precipitate was centrifuged at 8000 rpm for 5 min to obtain the precipitate. The precipitate was washed three times with 5 mL of methanol, and the supernatant was discarded after each wash. Finally, the precipitate was transferred to a vacuum drying oven preheated to 60 °C and dried at 60 °C for 24 h to obtain ZIF-8-NH2 material.

[0049] Comparative Example 3

[0050] ZIF-8@MON material was prepared. Triethylamine (5 mL) and toluene (10 mL) were mixed in a brown bottle, followed by the addition of ZIF-8 (100 mg), copper iodide (25 mg), and palladium dichloride bis(triphenylphosphine) chloride (3.4 mg). After sonication at room temperature for 15 min, the mixture was heated and stirred at 90 °C and 700 rpm for 1 h. Subsequently, 1,4-diiodobenzene (16 mg) and tetrakis(4-ethynylphenyl)methane (10 mg) were rapidly added, and the mixture was heated and stirred under the same conditions for another 4 h. After the reaction was complete, the mixture was cooled to room temperature, centrifuged at 8000 rpm for 5 min, and the precipitate was washed three times with methanol. Finally, the product was dried overnight in an oven to obtain the ZIF-8@MON material.

[0051] Comparative Example 4

[0052] Preparation of MON material: Triethylamine (5 mL) and toluene (10 mL) were mixed in a 20 mL brown bottle. Copper iodide (25 mg) and palladium dichloride bis(triphenylphosphine) chloride (3.4 mg) were added sequentially. After sonication at room temperature for 15 min, the mixture was heated and stirred at 90 °C and 700 rpm for 1 h. Subsequently, 1,4-diiodobenzene (16 mg) and tetra(4-ethynylphenyl)methane (10 mg) were rapidly added, and the mixture was heated and stirred under the same conditions for another 4 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged at 8000 rpm for 5 min, and the precipitate was washed three times with methanol. Finally, the product was dried in an oven overnight to obtain the MON material.

[0053] Example 2

[0054] The method for immersion extraction of multiple hydroxy polycyclic aromatic hydrocarbons in urine using the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction coated fiber obtained in Example 1 above includes the following steps:

[0055] (1) Accurately measure 5 mL of urine sample, add 10 μL of β-glucuronidase and 1 mL of HAc-NaAc buffer solution to adjust the pH of the urine sample to 5.5, and heat in a water bath at 37 ℃ for 4 h. Centrifuge the hydrolyzed urine sample at 4000 rpm for 10 min and collect the supernatant. Push the solid-phase microextraction coated fiber obtained above out of the fiber protective sleeve, immerse it in the mixed solution, and heat and stir at a constant rate of 55±1 ℃ and 700 rpm for 40 min to ensure that the sample and fiber coating are in full contact. Then, retract the solid-phase microextraction fiber into the fiber protective sleeve and quickly pull it out of the sample bottle.

[0056] (2) Static analysis. The solid-phase microextraction fiber after extraction was inserted into a 2 mL liquid phase vial containing a 3:1 mixture of methanol and water and allowed to stand at room temperature for 8 h to achieve efficient desorption and enrichment of the target compound.

[0057] Comparative Example 5

[0058] Keeping all operating steps unchanged, the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction coating fiber in Example 2 was replaced sequentially with ZIF-8, ZIF-8-NH2, ZIF-8@MON, and MON fibers.

[0059] Example 3

[0060] Hydroxypolycyclic aromatic hydrocarbons in the sample were determined using liquid chromatography-mass spectrometry.

[0061] The test conditions for liquid chromatography and mass spectrometry were as follows: a 2.1 mm × 100 mm, 1.8 μm C18 column was selected; the mobile phase was pure water and methanol; the flow rate was 0.3 mL / min; the run time was 13 min; and the gradient elution program for the liquid chromatography mobile phase was shown in Table 1. The column temperature was programmed at 40 ℃, and the injection volume was 10 μL.

[0062] Table 1 Gradient elution program for liquid chromatography mobile phase

[0063]

[0064] The ion source was an electrospray ionization source in negative ion mode, with a drying gas flow rate of 11 L / min and a drying gas temperature of 200 °C; the nebulizer pressure was 35 psi; the capillary voltage was 3500 V; the sheath gas temperature was 250 °C; and the sheath gas flow rate was 12 L / min. Selected ion scanning was used. Quantification was performed based on characteristic fragment ions with large molecular weights and high abundance. Specific fragment ion information is shown in Table 2.

[0065] Table 2. Quantitative information on ion pairs and collision energies of target compounds

[0066]

[0067] Comparative performance and analysis of Example 1 and Comparative Examples 1-4

[0068] 1. Scanning electron microscope image

[0069] The materials prepared in Example 1 and Comparative Examples 1-4, as well as the solid-phase microextraction coating material in Example 1, were characterized by scanning electron microscopy and energy dispersive spectroscopy. The results are as follows: Figure 2 , 3As shown. Scanning electron microscopy analysis revealed that ZIF-8 has a smooth surface and a regular rhombic dodecahedral structure with a size of approximately 200 nm. ZIF-8-NH2 maintains the same crystal form while increasing in size to approximately 500 nm, while MON exhibits a porous flocculent morphology with a size ranging from 500 nm to several micrometers. After composite formation, ZIF-8@MON forms irregular aggregates with a size of approximately 200 nm and constructs a continuous porous network. Further carboxyl functionalization yields ZIF-8-NH2@MON-2COOH particles with a size between tens and hundreds of nanometers, still exhibiting a tightly aggregated state and even more developed porosity. The fiber material prepared from it has a diameter of approximately 30 μm, a rough surface, and is interwoven into a three-dimensional network structure. Combined with the energy dispersive spectroscopy analysis of the solid-phase microextraction coating material in Example 1, it was confirmed that the elements such as C, N, O, and Zn are uniformly distributed.

[0070] 2. Infrared

[0071] The materials prepared in Example 1 and Comparative Examples 1-4 were structurally characterized, and the results are as follows: Figure 4 show.

[0072] 3150~3050 cm -1 In the range of 3450–3350 cm⁻¹, stretching vibration peaks of CH on the imidazole ring were observed in ZIF-8, ZIF-8-NH₂, and both types of composite materials. -1 At this point, ZIF-8-NH2 exhibits a symmetric / antisymmetric stretching vibration peak of -NH2, indicating that the amino group was successfully introduced into ZIF-8; 1650~1600 cm⁻¹ -1 At this location, the characteristic peak of the C=C conjugated double bond of MON is clearly visible, while ZIF-8-NH2@MON-2COOH has an additional peak at 1680 cm⁻¹ in this region. -1 The nearby C=O stretching vibration peak corresponds to the carboxyl functionalization of MON; 1550~1450 cm⁻¹ -1 In this region, the characteristic C=N vibrational peaks of the imidazole ring in ZIF-8 and ZIF-8-NH2 overlap with the skeletal vibrational peaks of MON, collectively constituting the complex absorption of the composite material in this region; 1500~1300 cm⁻¹ -1 In the range of 550–450 cm⁻¹, ZIF-8-NH₂@MON-2COOH exhibits a broad absorption peak due to hydrogen bonding between NH and CN groups. -1 At this point, all materials containing ZIF motifs exhibit characteristic stretching vibration peaks of Zn-N coordination bonds. These characteristic peaks at finer wavenumbers not only reflect the structural motifs of each material but also confirm the composite of ZIF and MON, the functionalization modification of MON, and the intermolecular hydrogen bonding in the composite system.

[0073] 3. BET specific surface area

[0074] The specific surface area and pore volume of the coating material in Example 1 were characterized, and the results are as follows: Figure 5 , 6 As shown, the BET specific surface area of ​​ZIF-8-NH2@MON-2COOH can reach approximately 1518.01 m². 2 / g, with an average pore volume and pore diameter of 1.354 cm. 3 / g and 3.56 nm indicate that the ZIF-8@MON-2COOH material has a well-developed pore structure and better pore characteristics, and can maintain a high pore volume over a wider pore width range, thus giving it stronger adsorption capacity and higher adsorption efficiency.

[0075] 4. Hydrophilicity

[0076] The contact angles of the solid-phase microextraction coating materials prepared in Example 1 and Comparative Examples 1-4 were characterized, and the results are as follows: Figure 7 As shown, the five materials—ZIF-8, ZIF-8-NH2, MON, ZIF-8@MON, and ZIF-8-NH2@MON-2COOH—exhibit significant differences in hydrophilicity and hydrophobicity. Specifically, ZIF-8 and ZIF-8-NH2 have similar contact angles, approximately 88° and 87° respectively, indicating a relatively neutral hydrophilic-hydrophobic balance. MON, however, exhibits extremely strong superhydrophobicity with a contact angle as high as 144°, while ZIF-8@MON also shows a significantly increased contact angle of 133°, indicating enhanced hydrophobicity compared to ZIF-8 alone. This helps reduce competition between water molecules and pollutants. In contrast, ZIF-8-NH2@MON-2COOH has a contact angle of 93°, and its moderate hydrophilicity is more conducive to interaction with the solvent, thereby improving the material's extraction and adsorption capacity for pollutants.

[0077] 5. Extraction effects of different materials on different pollutants

[0078] For the solid-phase microextraction (SPE) coating materials prepared in Examples 1 and Comparative Examples 1-4, seven pollutants—2-hydroxynaphthalene, 1-hydroxypyrene, 2-hydroxyphenanthrene, 4-hydroxyphenanthrene, 9-hydroxyphenanthrene, 2-hydroxy-9-fluorenone, and 1,8-dihydroxyanthraquinone—were extracted and adsorbed from urine medium using SPE. A high-performance liquid chromatography-triple quadrupole tandem mass spectrometry (HPLC-MS / MS) method was established to detect the pollutant content, thereby evaluating the extraction and adsorption performance of various materials. The results are as follows: Figure 8 As shown, the core-shell structured carboxyl-functionalized MON@ZIF-8-NH2 material exhibits the most significant extraction and adsorption effects for the aforementioned pollutants. This result fully demonstrates the effectiveness and excellent adsorption performance of the core-shell structured carboxyl-functionalized MON@ZIF-8-NH2 material in practical applications.

[0079] Comparative Example 6

[0080] The solvent for the analysis in step 4 of Example 1 was set to pure methanol, and the remaining steps were the same.

[0081] Comparative Example 7

[0082] The solvent for the analysis in step 4 of Example 1 was set to pure water, and the remaining steps were the same.

[0083] Comparative Example 8

[0084] The solvent for the analysis in step 4 of Example 1 was set to methanol:water = 3:1, and the remaining steps were the same.

[0085] Comparative Example 9

[0086] The solvent for the analysis in step 4 of Example 1 was set to methanol:water = 1:1, and the other steps were the same.

[0087] Comparative Example 10

[0088] The solvent for the analysis in step 4 of Example 1 was set to methanol:water = 1:3, and the remaining steps were the same.

[0089] Example 4

[0090] The extraction and adsorption effects of pollutants on the carboxyl-functionalized MON@ZIF-8-NH2 material under different solvent conditions in Comparative Examples 6-10 and Example 2 are as follows: Figure 9 As shown, the extraction and adsorption effect of pollutants on the carboxyl-functionalized MON@ZIF-8-NH2 material is optimal when the solvent ratio of methanol to water is 3:1.

[0091] Example 5

[0092] The time and temperature of the core-shell structure carboxyl-functionalized MON@ZIF-8 fibers during extraction and desorption were optimized using a Box-Behnken design experiment.

[0093] Figure 10 The response surface methodology (RSM) results of the extraction and desorption process of core-shell carboxyl-functionalized MON@ZIF-8 fibers, optimized based on a Box-Behnken design, are presented intuitively. In the figure, the horizontal axis (A) represents extraction time, the horizontal axis (B) represents extraction temperature, the horizontal axis (C) represents desorption time, and the vertical axis (Y) represents the corresponding peak area, reflecting the extraction efficiency. Through analysis... Figure 10Based on the response surface morphology, experimental point distribution, and contour characteristics of (a), (b), and (c) in the model, combined with the scientific validity of the Box-Behnken design and the reliability of the model, the optimal conditions were determined: extraction time 40.493 min, extraction temperature 56.099 ℃, and desorption time 8.407 h. Considering practical conditions, the final extraction time was determined to be 40 min, extraction temperature 55 ℃, and desorption time 8.5 h. Under these conditions, the peak area reached its maximum value, and the peak area error between the reagent-optimal conditions and the theoretically optimal conditions was less than 8%. These optimized parameters not only possess high accuracy and reliability in theory but also demonstrate good operability and practicality in real-world applications, providing strong guidance for improving the extraction efficiency of core-shell structured carboxyl-functionalized MON@ZIF-8 fibers.

[0094] Example 6

[0095] Under optimal extraction conditions—methanol:water = 3:1 as the solvent, extraction temperature of 55 °C for 40 min, elution time of 8.5 h, and elution temperature of 30 °C—seven mixed standard solutions of different concentrations were prepared by diluting with ultrapure water for extraction, and a standard curve was established.

[0096] The linear equations, linear ranges, correlation coefficients, limits of detection (LODs) and limits of quantification (LOQs) for the seven hydroxyl polycyclic aromatic hydrocarbons were calculated using peak area integral quantification. The LODs and LOQs were calculated based on a signal-to-noise ratio of 3 and 10, respectively. The results are shown in Table 3.

[0097] This method exhibits a wide linear range, from 0.2 to 40 μg / L, with a low limit of detection (LOD) of 0.04 to 0.32 μg / L and a limit of quantitation (LOQ) of 0.14 to 1.05 μg / L. Seven hydroxyl polycyclic aromatic hydrocarbons showed good linearity over a wide concentration range, with correlation coefficients R0. 2 The value is greater than 0.999, meeting the requirements for quantitative analysis. The relative standard deviation (n=6) of the same coating ranges from 7.41% to 18.42%, indicating that the coating preparation method has good reproducibility. The relative standard deviation was calculated based on samples from six parallel experiments, denoted as n=6. The data show that this optimized method can be used for the analysis of trace hydroxyl polycyclic aromatic hydrocarbons. Furthermore, the core-shell structured carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction fiber is sensitive and rapid, reducing many complex operations; the extraction process does not require organic solvents, making it a green technology that meets the requirements of modern analytical development.

[0098] Table 3. Linear range, correlation coefficient, limit of detection, limit of quantitation, and precision of ZIF-8-NH2@MON-2COOH fiber in the determination of seven hydroxy polycyclic aromatic hydrocarbons in urine samples (n=6)

[0099]

[0100] Example 7

[0101] Urine samples were collected and pretreated. The concentrations of seven hydroxy polycyclic aromatic hydrocarbons were determined by a self-made shell-core structure carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction fiber at 0.1 ug / L, 1 ug / L, and 10 ug / L. The average recovery rate was determined by the standard addition method, as shown in Table 4.

[0102] The recoveries of spiked 10 μg / L samples ranged from 85.20% to 115.85%, with a relative standard deviation (RSD) of less than 15.67%; the recoveries of spiked 1 μg / L samples ranged from 72.14% to 102.66%, with an RSD of less than 19.83%; and the recoveries of spiked 0.1 μg / L samples ranged from 71.91% to 109.40%, with an RSD of less than 16.47%. The recoveries of the substitute 2-hydroxynaphthalene-D8 ranged from 74.3% to 105.4%, meeting the analytical requirements. These results indicate that the established liquid chromatography-mass spectrometry (LC-MS) method has good accuracy and precision and can be used for the analysis and detection of hydroxyl polycyclic aromatic hydrocarbons in urine samples.

[0103] Table 4. Spike recoveries and concentrations of seven hydroxy polycyclic aromatic hydrocarbons in urine determined by this method.

[0104]

[0105] Under the chromatographic conditions described in this invention, such as Figure 11 As shown, the baselines of the peaks are well separated, and the peak area and concentration exhibit a good linear relationship. At the same time, the chromatographic baseline is stable, indicating that the chromatographic method can efficiently and accurately separate and identify the compounds.

[0106] Example 8

[0107] The method developed was used to detect urine samples from the population. After enzymatic digestion, the collected urine samples were analyzed using a self-prepared carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction fiber coating. The results are shown in Table 5.

[0108] Table 5 shows that all target pollutants were detected. 1-Hydroxypyrene had the highest detection rate, with a concentration of 2.26 μg / L; 2-hydroxyphenanthrene and 9-hydroxyphenanthrene had relatively high detection rates, with concentrations of 0.47 μg / L and 0.78 μg / L, respectively; 2-hydroxynaphthalene and 4-hydroxyphenanthrene had relatively low detection rates, with concentrations of 0.21 μg / L and 0.19 μg / L, respectively; while 2-hydroxy-9-fluorenone had the lowest detection rate, with a concentration of only 0.25 μg / L, and was mostly undetectable. The detection of these seven OH-PAHs pollutants in actual urine samples fully validated the good stability and reliability of this method, providing reliable technical support and a practical basis for the accurate detection of OH-PAHs in urine samples.

[0109] Table 5. Concentrations of seven hydroxy polycyclic aromatic hydrocarbons in actual human urine determined by this method (unit: μg / L)

[0110]

[0111] Nd: Not detected.

[0112] Based on peak area, the performance of the self-made carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction fiber was compared with that of commercial 7 μm PDMS, commercial 100 μm PDMS, and commercial 65 μm PDMS / DVB fiber.

[0113] Comparative Example 11

[0114] The extraction effects of homemade fibers and commercially available fibers were compared, and the results are as follows: Figure 12 As shown, the retention times of all target analytes were completely consistent on both the self-made and commercial fibers, ensuring the stability of retention behavior. Regarding extraction efficiency, the self-made fiber's extraction efficiency for low-retention targets such as 2-hydroxynaphthalene and 2-hydroxy-9-fluorenone was comparable to and higher than that of commercial 100 µm PDMS. However, for high-retention targets such as 2-hydroxyphenanthrene series OH-PAHs and 1,8-dihydroxyanthraquinone, commercial 100 µm PDMS completely lost its extraction capability, while the peak area of ​​the self-made fiber was significantly higher than that of commercial 7 µm PDMS. This demonstrates the superior extraction performance of the self-made fiber for various target analytes, especially high-retention OH-PAHs, highlighting its significant advantages in target analyte applicability and extraction efficiency.

Claims

1. A method for preparing a carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material, characterized in that, Includes the following steps: (1) Place ZIF-8-NH2 powder in a mixed solvent of toluene and triethylamine, and add copper iodide and palladium dichloride of bis(triphenylphosphine) in sequence, and react under heating and stirring conditions; (2) Add 2,5-dibromoterephthalic acid and tetra(4-ethynylphenyl)methane, and continue heating and stirring; after the reaction is completed, centrifuge, wash and dry the mixture to obtain a shell-core structure carboxyl functionalized MON@ZIF-8-NH2 solid phase microextraction material with ZIF-8-NH2 as the core and MONs-2COOH as the shell.

2. The method for preparing carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material according to claim 1, characterized in that, The mass ratios of ZIF-8-NH2, bis(triphenylphosphine)palladium dichloride, copper iodide, and 2,5-dibromoterephthalic acid to tetrakis(4-ethynylphenyl)methane are 7.5:1~10:1, 0.25:1~0.35:1, 2:1~2.5:1, and 1.5~1.6:1, respectively.

3. The method for preparing carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material according to claim 1, characterized in that, In step (1), the volume ratio of toluene to triethylamine is 2:1 to 3:

1.

4. The method for preparing carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material according to claim 1, characterized in that, In step (1), the heating temperature is 80~100 ℃ and the heating time is 0.5~2 h; in step (2), the heating is carried out under the same conditions for 3~5 h.

5. The application of a carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material obtained by the method of claim 1 in the extraction of hydroxy polycyclic aromatic hydrocarbons from urine.

6. The application according to claim 5, characterized in that, The carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material was fixed on a support substrate using a physical coating method to obtain a solid-phase microextraction coated fiber. The solid-phase microextraction coated fiber was then immersed in an enzymatically hydrolyzed urine sample and extracted by stirring.

7. The application according to claim 6, characterized in that, The preparation process of the solid-phase microextraction coated fiber is as follows: dilute silicone adhesive with n-hexane to obtain silicone adhesive diluent, coat the diluent onto the support substrate, insert the support substrate into the carboxyl-functionalized MON@ZIF-8-NH2 solid-phase microextraction material obtained in claim 1, rotate repeatedly to obtain a coating with a thickness of 40~50 μm and a length of 1.5~3 cm, and dry at 60~80 ℃ for 18~24 h to obtain the solid-phase microextraction coated fiber.

8. The application according to claim 5, characterized in that, The extraction temperature was 50~60 ℃, and the extraction time was 30~40 min.

9. The application according to claim 5, characterized in that, After extraction, the coated fiber is placed in a mixed solution of methanol and water for static analysis; the mass ratio of methanol to water is 2:1 to 3:1; the analysis temperature is 25 to 30 °C, and the analysis time is 8 to 10 h.

10. The application according to claim 6, characterized in that, The specific process of enzymatic hydrolysis of urine samples is as follows: add 10-15 μL of β-glucuronidase to 5-10 mL of urine sample, then add 1-3 mL of acetate-sodium acetate buffer solution to adjust the pH to 5-6, and heat in a water bath at 30-40 ℃ for 3-5 h.

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