Ru-coated Ni-MOF material, preparation method, solid-phase microextraction probe and application

Abstract

The invention relates to the technical field of solid-phase microextraction probes and veterinary drug detection, in particular to a Ru-coated Ni-MOF material, a preparation method of the Ru-coated Ni-MOF material, a solid-phase microextraction probe and application. According to the preparation method, Ni-MOF is taken as a matrix, a solvothermal method is adopted, a metal node Ru is partially doped and introduced into the Ni-MOF, a Ru-coated Ni-MOF nanosheet with a Ni-O-Ru coordination bond is synthesized under the assistance of foamed nickel, and a Ru-coated Ni-MOF material is obtained; the adsorption capacity of the material to enrofloxacin, norfloxacin, sulfachlorpyridazine and phthalocyanine thiazole is 34.64 mg / g to 113.31 mg / g. A Ru-coated Ni-MOF material is used as a raw material, in a solvent system, the Ru-coated Ni-MOF material and polyacrylonitrile are mixed, an extraction coating is formed on the surface of a substrate through an electrostatic spinning method, then the substrate is soaked in ethyl alcohol, and the solid-phase microextraction probe is obtained after drying.

Description

Technical Field

[0001] This invention relates to the field of solid-phase microextraction probes and veterinary drug detection technology, specifically to Ru@Ni-MOF materials and their preparation methods, solid-phase microextraction probes and their applications. Background Technology

[0002] Sulfonamides and fluoroquinolones, as synthetic broad-spectrum antibacterial agents, are widely used in veterinary medicine for disease prevention and treatment. However, their improper use leads to residues in animal-derived foods and aquatic ecosystems, which can then enter the human body through the food chain, causing health risks such as allergic reactions and kidney dysfunction. Therefore, it is crucial to develop sensitive and selective analytical techniques for ultra-trace residues in complex food matrices.

[0003] Sample preparation is a crucial step in achieving the above-mentioned detections, and its core lies in removing complex matrices and enriching trace antibiotic residues. Existing enrichment techniques include solid-phase extraction, liquid-liquid extraction, and magnetic solid-phase extraction. Among these, solid-phase microextraction (SPE) has significant advantages in analytical detection due to its solvent-free nature, ease of operation, and ability to integrate sampling, extraction, concentration, and separation steps without the need for complex filtration or elution.

[0004] Solid-phase microextraction (SPE) coatings serve as functional carriers for analyte enrichment in SPE technology. Through intermolecular forces between the coating and the target analyte, they achieve selective adsorption and enrichment, directly determining the extraction efficiency, selectivity, and detection sensitivity of SPE. Although commercially available SPE coatings include polydimethylsiloxane, polyacrylate, and polydimethylsiloxane / divinylbenzene, their selectivity and adsorption efficiency are often limited. Furthermore, the adsorption capacity of these coatings is also limited by the small surface area of ​​the fibrous substrate and the lack of functional binding sites, making it difficult to meet the demand for efficient enrichment of trace antibiotic residues in complex food matrices.

[0005] In recent years, various coating materials for solid-phase microextraction (SPE) technologies have been developed, including graphene and metal-organic frameworks (MOFs). Among them, MOFs, composed of metal nodes and organic ligands, have shown great potential in adsorption, separation, and catalysis due to their high specific surface area, tunable porosity, and structural diversity. Single-metal MOFs have been used as adsorbents for various food contaminants, such as heavy metals, antibiotics, dyes, pesticides, and heterocyclic compounds. However, single-metal MOFs have limitations such as a limited number of active sites and insufficient stability under harsh conditions, which to some extent restricts their application in practical detection. Summary of the Invention

[0006] To address the technical problems of limited active sites and insufficient stability under harsh conditions in the aforementioned single-metal MOFs, this invention provides a Ru@Ni-MOF material and its preparation method, a solid-phase microextraction probe, and its applications.

[0007] The first objective of this invention is to provide a method for preparing Ru@Ni-MOF materials, comprising the following steps: Using Ni-MOF as a matrix, a solvothermal method was used to partially dope Ni-MOF to introduce metal nodes Ru. Two-dimensional Ru@Ni-MOF nanosheets with Ni-O-Ru coordination bonds were synthesized with the assistance of nickel foam, resulting in Ru@Ni-MOF material. The molar ratio of Ni to Ru in Ru@Ni-MOF material was 50:1 to 50.

[0008] Preferably, the specific preparation method of Ru@Ni-MOF material is as follows: In a solvent system, ligands, Ni source and Ru source are mixed and nickel foam is added. The mixture is then subjected to a solvothermal reaction at 120℃~160℃ to synthesize two-dimensional Ru@Ni-MOF nanosheets with Ni-O-Ru coordination bonds, thus obtaining Ru@Ni-MOF materials.

[0009] Preferably, the molar ratio of ligand, Ni source, and Ru source is 50:50:1 to 50. When the Ru source doping amount is too high, the two-dimensional layered structure of Ni-MOF is difficult to maintain, resulting in a sharp decrease in specific surface area and porosity, which in turn weakens the adsorption capacity of Ru@Ni-MOF two-dimensional nanosheets for antibiotics. Too low Ru source doping amount results in a thinner and more rigid two-dimensional layered structure of Ni-MOF, which is prone to breakage during repeated use, thus affecting its reusability.

[0010] Preferably, the ligand is terephthalic acid, 2,5-dihydroxyterephthalic acid, p-mercaptoterephthalic acid, or 2-aminoterephthalic acid. Amino ligands, due to their strong coordination ability, form stable coordination bonds with Ni and Ru, thereby influencing the growth direction and morphology of the material, resulting in a multi-layered, plate-like structure. The introduction of hydroxyl ligands alters the surface properties and growth mechanism of the material, making it more prone to forming granular or blocky structures. Mercapto ligands, due to their high reactivity and coordination selectivity, form specific coordination structures with Ni and Ru during synthesis, resulting in a uniform granular morphology. More preferably, the ligand is terephthalic acid.

[0011] Preferably, the solvothermal reaction time is 10h to 14h.

[0012] It should be noted that nickel foam participates in the redox reaction during the synthesis process. In this reaction, nickel foam acts as both a reactant and an electron donor, playing a crucial role in connecting the formation of the Ni-MOF framework with the regulation of Ru species. Both nickel foam and the nickel source jointly provide Ni for the construction of Ru@Ni-MOF materials. 2+ Meanwhile, nickel foam acts as a reducing agent, reducing the Ru precursor to the target valence state. It also assists in electron transfer through its own conductive structure, ensuring efficient reaction.

[0013] Preferably, the solvent is a mixed solution of N,N-dimethylformamide, ethanol and water, wherein the volume ratio of N,N-dimethylformamide, ethanol and water is 18:2:1.

[0014] Preferably, the Ni source is nickel chloride hexahydrate. Of course, other Ni sources can be selected according to actual needs. Preferably, the Ru source is RuCl3·xH2O. Of course, other Ru sources can be selected according to actual needs.

[0015] A second objective of this invention is to provide a Ru@Ni-MOF material, which is prepared by the above-described preparation method.

[0016] Preferably, the specific surface area of ​​the Ru@Ni-MOF material is 50 m². 2 / g~600m 2 / g, with a pore size distribution of 12nm~23nm.

[0017] The third objective of this invention is to provide a solid-phase microextraction probe, comprising a substrate and an extraction coating. The solid-phase microextraction probe is obtained by using Ru@Ni-MOF material as raw material, mixing Ru@Ni-MOF material and polyacrylonitrile in a solvent system, forming an extraction coating on the surface of the substrate by electrospinning, and then immersing it in ethanol and drying it.

[0018] Preferably, the ratio of Ru@Ni-MOF material, polyacrylonitrile, and solvent is 75–225 mg: 75–225 mg: 3 mL.

[0019] Preferably, the electrospinning conditions are: voltage of 20kV, spray rate of 17μL / min, and time of 20min to 60min.

[0020] Preferably, the solvent is N,N-dimethylformamide.

[0021] Preferably, the thickness of the extraction coating is 100μm to 140μm and the length is 0.8cm to 1.2cm.

[0022] Preferably, the substrate is a stainless steel rod with a diameter of 0.9 mm to 1.1 mm.

[0023] The fourth objective of this invention is to provide an application of a solid-phase microextraction probe in veterinary drug detection.

[0024] Preferably, the veterinary drug is at least one of enrofloxacin, norfloxacin, sulfachlorpyridazine, and phthalimidethiazide.

[0025] Compared with the prior art, the present invention has the following technical effects: 1. This invention uses Ni-MOF as a matrix and employs a solvothermal method to partially dope Ni-MOF to introduce metal nodes Ru. With the assistance of nickel foam, Ru@Ni-MOF nanosheets with Ni-O-Ru coordination bonds are synthesized, achieving diversified coordination sites and electronic structure control of the metal center to obtain Ru@Ni-MOF materials. Through the synergistic effect of Ni-O-Ru chemical bonds, electron transfer efficiency is significantly promoted, optimizing the adsorption and desorption processes of reaction intermediates. Simultaneously, this unique bonding method accelerates charge migration, effectively reduces the reaction activation energy, and further enhances the binding strength between the metal nanoparticles and the MOF support, thereby effectively inhibiting the aggregation or detachment of active sites and significantly improving the long-term stability of the adsorption material. This invention solves the technical problems of limited active sites and insufficient stability under harsh conditions in single-metal MOFs.

[0026] 2. This invention uses Ru@Ni-MOF material as raw material and prepares an extraction coating through electrospinning. This coating exhibits a stronger synergistic adsorption mechanism of π-π stacking, coordination, and electrostatic interaction, with adsorption capacities for enrofloxacin, norfloxacin, sulfachlorpyridazine, and phthalimidethiazide ranging from 34.64 mg / g to 113.31 mg / g, representing an adsorption capacity increase of approximately 82% compared to single-metal Ni-MOF. Simultaneously, the nanofiber-like coating structure provides a high specific surface area and rapid mass transfer channels, significantly improving the adsorption kinetics and peak capacity of the target molecules.

[0027] 3. The electrospun coating prepared by electrospinning in this invention has a simple process and can be mass-produced. The coating has strong adhesion to the substrate and can maintain stable performance after 200 cycles, meeting the requirements of high-throughput repetitive detection.

[0028] 4. The solid-phase microextraction probe prepared in this invention has a detection limit as low as ppb in complex matrices such as milk and pork, a wide linear range, and good reproducibility, which meets the requirements of the National Food Safety Standards GB 31650-2021 and GB 3160.1-2022. Furthermore, the prepared solid-phase microextraction probe can be used for the pre-enrichment of various organic pollutants in wastewater, antibiotics in environmental water bodies, and other biological samples, and has good versatility and scalability.

[0029] 5. The extraction method of the present invention does not require complex sample pretreatment, and the overall process is time-saving and solvent-saving, making it suitable for rapid detection applications in laboratories and on-site, and has good industrialization and promotion value. Attached Figure Description

[0030] Figure 1Scanning electron microscope (SEM) images, high-resolution transmission electron microscope (HRTEM) images, and electron energy dispersive spectroscopy (EEDS) images of the Ni-MOF material prepared in Comparative Example 1 and Ru@Ni-MOF materials with different Ru doping amounts are shown. Specifically, (a) is the SEM image of Ni-MOF, (a1) is the HRTEM image of Ni-MOF, (a2) is the area scan of Ni-MOF, (a3) ​​is the Ni / O elemental distribution map of Ni-MOF, (a4) is the Ni elemental distribution map of Ni-MOF, and (a5) is the O elemental distribution map of Ni-MOF; (b) is the SEM image of Ru@Ni-MOF-1, (b1) is the HRTEM image of Ru@Ni-MOF-1, (b2) is the area scan of Ru@Ni-MOF-1, and (b3) is the Ni / Ru elemental distribution map of Ru@Ni-MOF-1. The distribution diagrams are as follows: (b4) is the Ni element distribution diagram of Ru@Ni-MOF-1, (b5) is the Ru element distribution diagram of Ni-MOF-1; (c) is the scanning electron microscope image of Ru@Ni-MOF-2, (c1) is the high-resolution transmission electron microscope image of Ru@Ni-MOF-2, (c2) is the surface scan image of Ru@Ni-MOF-2, (c3) is the mixed distribution diagram of Ni and Ru elements in Ru@Ni-MOF-2, (c4) is the Ni element distribution diagram of Ru@Ni-MOF-2, (c5) is the Ru element distribution diagram of Ni-MOF-2; (d) is the scanning electron microscope image of Ru@Ni-MOF-3. The images are as follows: (d1) is a high-resolution transmission electron microscope (TEM) image of Ru@Ni-MOF-3; (d2) is a surface scan of Ru@Ni-MOF-3; (d3) is a mixed distribution map of Ni and Ru elements in Ru@Ni-MOF-3; (d4) is a Ni element distribution map of Ru@Ni-MOF-3; (d5) is a Ru element distribution map of Ru@Ni-MOF-3. (e) are the scanning electron microscope (SEM) images of Ru@Ni-MOF-4: (e1) is a high-resolution TEM image of Ru@Ni-MOF-4; (e2) is a surface scan of Ru@Ni-MOF-4; (e3) is a mixed distribution map of Ni and Ru elements in Ru@Ni-MOF-3. (e4) is the Ni element distribution map of Ru@Ni-MOF-4, (e5) is the Ru element distribution map of Ru@Ni-MOF-4; (f) is the scanning electron microscope image of Ru@Ni-MOF-5, (f1) is the high-resolution transmission electron microscope image of Ru@Ni-MOF-5, (f2) is the area scan image of Ru@Ni-MOF-5, (f3) is the Ni and Ru element distribution map of Ru@Ni-MOF-5, (f4) is the Ni element distribution map of Ru@Ni-MOF-5, and (f5) is the Ru element distribution map of Ru@Ni-MOF-5.

[0031] Figure 2Scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) images of Ru@Ni-MOF synthesized with different ligands are shown. (a) is an SEM image of Ru@Ni-MOF-NH2 synthesized with amino terephthalic acid; (b) is an SEM image of Ru@Ni-MOF-OH synthesized with hydroxylated terephthalic acid; (c) is an SEM and HRTEM image of Ru@Ni-MOF-SH synthesized with mercaptolated terephthalic acid; (d) is an HRTEM image of Ru@Ni-MOF-NH2 synthesized with amino terephthalic acid; (e) is an HRTEM image of Ru@Ni-MOF-OH synthesized with hydroxylated terephthalic acid; and (f) is an HRTEM image of Ru@Ni-MOF-SH synthesized with mercaptolated terephthalic acid.

[0032] Figure 3 The water contact angles are those of the Ni-MOF material prepared in Comparative Example 1 and the Ru@Ni-MOF materials synthesized with different ligands. (a) represents the water contact angle of the Ni-MOF material; (b) represents the water contact angle of the Ru@Ni-MOF synthesized with terephthalic acid; (c) represents the water contact angle of the Ru@Ni-MOF synthesized with 2-aminoterephthalic acid; (d) represents the water contact angle of the Ru@Ni-MOF synthesized with 2,5-dihydroxyterephthalic acid; and (e) represents the water contact angle of the Ru@Ni-MOF synthesized with p-mercaptoterephthalic acid.

[0033] Figure 4 The zeta potentials are those of the Ni-MOF material prepared in Comparative Example 1 and the Ru@Ni-MOF materials synthesized with different ligands. (a) represents the zeta potential of the Ni-MOF material; (b) represents the zeta potential of Ru@Ni-MOF synthesized with terephthalic acid; (c) represents the zeta potential of Ru@Ni-MOF-NH2 synthesized with aminated terephthalic acid; (d) represents the zeta potential of Ru@Ni-MOF-OH synthesized with hydroxylated terephthalic acid; and (e) represents the zeta potential of Ru@Ni-MOF-SH synthesized with thiolized terephthalic acid.

[0034] Figure 5The N2 adsorption-desorption isotherms and pore size distribution at 77 K are shown for the Ni-MOF material prepared in Comparative Example 1 and the Ru@Ni-MOF materials synthesized with different ligands. Among them, (a) is the N2 adsorption-desorption isotherm of Ni-MOF material, with the inset showing the pore size distribution at 77 K; (b) is the N2 adsorption-desorption isotherm of Ru@Ni-MOF material synthesized from terephthalic acid, with the inset showing the pore size distribution at 77 K; (c) is the N2 adsorption-desorption isotherm of Ru@Ni-MOF-NH2 synthesized from aminated terephthalic acid, with the inset showing the pore size distribution at 77 K; (d) is the N2 adsorption-desorption isotherm of Ru@Ni-MOF-OH synthesized from hydroxylated terephthalic acid, with the inset showing the pore size distribution at 77 K; and (e) is the N2 adsorption-desorption isotherm of Ru@Ni-MOF-SH synthesized from mercaptolated terephthalic acid, with the inset showing the pore size distribution at 77 K.

[0035] Figure 6 The adsorption energy absorption of four target compounds is compared between the Ni-MOF materials synthesized in Comparative Examples 1 and 2, and the Ru@Ni-MOF materials with different Ru doping amounts. Among them, (a) is enrofloxacin, (b) norfloxacin, (c) phthalimidethiazole, and (d) sulfachlorpyridazine.

[0036] Figure 7 X-ray photoelectron spectra of the Ru@Ni-MOF prepared in Example 1 and the O (a), Ru (b), and Ni (c) elements after adsorption of sulfathiazole, sulfachlordazine, enrofloxacin, and norfloxacin.

[0037] Figure 8 The molecular docking configuration optimized for energy minimization is shown, illustrating the binding orientation and interaction between the Ru@Ni-MOF material prepared in Example 1 and phthalimidethiazole (a), sulfachlordazine (b), enrofloxacin (c), and norfloxacin (d).

[0038] Figure 9 The curves show the optimization of electrospinning conditions and solid-phase microextraction parameters. (a) is the mass percentage-absolute recovery curve of Ru@Ni-MOF; (b) is the electrospinning time-absolute recovery curve; (c) is the sample volume-absolute recovery curve; (d) is the NaCl concentration-absolute recovery curve; (e) is the stirring speed-absolute recovery curve; (f) is the extraction temperature-absolute recovery curve; (g) is the extraction time-absolute recovery curve; (h) is the desorption solvent-absolute recovery histogram; and (i) is the desorption time-absolute recovery curve.

[0039] Figure 10The figure shows the reusability test results of the Ru@Ni-MOF-solid phase microextraction probe prepared in Example 1. Among them, (a) is the residual amount of antibiotics in the coating after repeated elution of Ru@Ni-MOF-solid phase microextraction probe; (b) is a bar chart of the absolute recovery rate of the reusability of Ru@Ni-MOF-solid phase microextraction probe; (c) is a bar chart of the absolute recovery rate of the reusability of Ru@Ni-MOF-solid phase microextraction probe from the same batch and different batches; where 1, 2, and 3 are three solid phase microextraction probes from the same batch; 4, 5, and 6 are three solid phase microextraction probes from three different batches; (d) is a comparison chart of the extraction efficiency of Ru@Ni-MOF-solid phase microextraction probe and four commercial solid phase microextraction probes under optimal extraction and desorption conditions; where 1 is Ru@Ni-MOF-solid phase microextraction probe; 2 is PDMS / DVB-solid phase microextraction probe; 3 is PDMS-solid phase microextraction probe; 4 is PDMS / CAR / DVB-solid phase microextraction probe; and 5 is PA-solid phase microextraction probe. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] A suitable coating preparation method can not only make the coating more durable and long-lasting, but also reduce experimental errors. Currently, methods for preparing nanomaterial coatings include self-assembly, electrochemical deposition, and electrospinning. Among these, electrospinning stands out because it forms microfibers from a viscous solution with a certain degree of elasticity through electrostatic stretching. This method is simple to operate, allows for immediate adjustment of operating parameters, and produces nanofibers with good uniformity and a large specific surface area, making it an effective method for preparing extraction coatings.

[0043] This invention uses Ni-MOF as a matrix and employs a solvothermal method to partially dope Ru metal nodes into the Ni-MOF, synthesizing two-dimensional Ru@Ni-MOF nanosheets with Ni-O-Ru chemical bonds with the assistance of nickel foam, thus obtaining Ru@Ni-MOF material. Then, using Ru@Ni-MOF material as raw material, an extraction coating is formed on the surface of the substrate by electrospinning to obtain a solid-phase microextraction probe. Ru@Ni-MOF has a large specific surface area and mesopore size, which is beneficial for the exposure of active sites. Furthermore, due to its ultrathin characteristics, it has a high surface area-to-volume ratio, resulting in high extraction efficiency and fast mass transfer rate. The electrospinning method has advantages such as uniform coating, cost-effectiveness, reusability, and good stability. The prepared nanofibers have advantages such as high specific surface area and rapid mass transfer kinetics, which can significantly improve the active adsorption sites of the obtained solid-phase microextraction probe.

[0044] The technical solution of the present invention will be further described below through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0045] In the following examples, terephthalic acid (H2BDC) was used with a purity of 99%; N,N-dimethylformamide (DMF) was used with a purity of 99.5%; methanol was chromatographically pure with a purity ≥99.9%; ethanol was analytically pure with a purity ≥99.7%; ruthenium chloride hydrate was used with a purity of 99%; nickel chloride hexahydrate was used with a purity of 99%; polyacrylonitrile (PAN) was used with an average molecular weight of 85,000; the nickel foam had a size of 1.0cm × 3.0cm; and phthalylsulfathiazole, sulfachlordazine, enrofloxacin, and norfloxacin were all purchased from Maclean Biochemical Technology Co., Ltd. in Shanghai, China.

[0046] In the following embodiments, four commercially available solid-phase microextraction (SPE) probes—PDMS / DVB SPE probe, PDMS SPE probe, PDMS / CAR / DVB SPE probe, and PA SPE probe—were sourced from Merck in Shanghai, China. Headspace vials and caps were also purchased from Merck in Shanghai, China. A scanning electron microscope (SEM) was used, an S-3700N instrument from Hitachi, Japan.

[0047] In the following examples, the room temperature was 25±5℃. The 0.2% formic acid aqueous solution was prepared by taking 183 μL of 90% formic acid and diluting it with water to a final volume.

[0048] Example 1 A method for preparing a Ru@Ni-MOF solid-phase microextraction probe includes the following steps: Step 1, Preparation of Ru@Ni-MOF material: 5 mmol of terephthalic acid, 5 mmol of NiCl2·6H2O, and 0.5 mmol of RuCl3·xH2O were dissolved in a mixed solution of 180 mL DMF, 20 mL ethanol, and 10 mL water. After stirring for 30 minutes, the solution was transferred to a 500 mL Teflon-lined autoclave, and dried nickel foam was placed against the inner wall of the liner. The autoclave was then placed in a muffle furnace and heated at 140 °C for 12 h. After cooling, the reacted nickel foam was removed and washed three times each with water and ethanol. The sample was then dried in a vacuum drying oven at 60 °C for 24 h to obtain the Ru@Ni-MOF material.

[0049] Step 2, Preparation of the electrospinning solution containing Ru@Ni-MOF: Polyacrylonitrile and DMF are mixed, and the mixture is heated to 80℃ and magnetically stirred to completely dissolve the polyacrylonitrile and mix it evenly with DMF. Then, the Ru@Ni-MOF material obtained in Step 1 is added, and the mixture is stirred for 24 hours to obtain the electrospinning solution containing Ru@Ni-MOF. In the electrospinning solution, the ratio of Ru@Ni-MOF material, polyacrylonitrile and DMF is 150mg:150mg:3mL.

[0050] Step 3: Forming a Ru@Ni-MOF coating on the stainless steel rod surface: The stainless steel rod surface is repeatedly cleaned with water and ethanol to remove oil stains and impurities, and then dried for later use. The diameter of the bare stainless steel rod is 0.9 mm to 1.1 mm. The cleaned stainless steel rod is fixed on a motor, and the Ru@Ni-MOF-containing electrospinning solution obtained in Step 2 is placed in a handheld electrospinning apparatus for electrospinning. The handheld electrospinning apparatus is used to coat the surface of the stainless steel rod to form a Ru@Ni-MOF coating. The electrospinning apparatus voltage is 20 kV, the flow rate is 17 μL / min, and the electrospinning time is 40 min. The distance from the tip of the syringe needle to the tip of the stainless steel rod is 20 cm, and the inner diameter of the spinning needle is 0.6 mm. The thickness of the Ru@Ni-MOF coating formed on the stainless steel rod surface is 107–128 μm, and the length is 0.8 cm to 1.2 cm.

[0051] Step 4, Preparation of Ru@Ni-MOF-solid-phase microextraction probe: A stainless steel rod with a Ru@Ni-MOF coating was immersed in ethanol for 1 hour to promote the solvent exchange reaction. Then it was placed in a drying oven at 70°C for 12 hours to obtain the Ru@Ni-MOF-solid-phase microextraction probe.

[0052] Comparative Example 1 A method for preparing a Ni-MOF-solid-phase microextraction probe includes the following steps: The difference between Comparative Example 1 and Example 1 is as follows: RuCl3·xH2O was not added.

[0053] Comparative Example 2 A method for preparing a Ni-MOF-solid-phase microextraction probe includes the following steps: The difference between Comparative Example 2 and Example 1 is as follows: No RuCl3·xH2O was added, and the mixed solution in step 1 was treated with ultrasound.

[0054] Example 2 A method for preparing a Ru@Ni-MOF solid-phase microextraction probe is basically the same as that in Example 1, except that the preparation parameters of the Ru@Ni-MOF material are different, including the molar ratio of NiCl2·6H2O and RuCl3·xH2O and the ligands, as shown in Table 1.

[0055] Table 1 Preparation parameters and conditions of Ru@Ni-MOF materials To investigate the effects of Ru doping levels and different ligands on the morphology and structure of Ru@Ni-MOF materials, Ru@Ni-MOF materials were prepared according to the parameters in Table 1, and their morphology was analyzed. The results are as follows: Figure 1 and Figure 2 As shown.

[0056] like Figure 1 As shown in (a) to (f), Ru@Ni-MOF exhibits a typical two-dimensional layered structure with large sheet-like morphology. The layers are tightly stacked, forming a wrinkle-like structure. This structure is beneficial for increasing the specific surface area and providing more opportunities for the exposure of active sites. Compared with the Ni-MOF material prepared in Comparative Example 1, Ru@Ni-MOF still exhibits obvious layered structure characteristics after the addition of Ru. However, the size of the sheet-like structure is reduced to a certain extent, and some fine wrinkles and unevenness appear on the surface. This may be because the introduction of Ru affects the growth process of Ni-MOF, thereby changing its morphology accordingly. In the initial stage of introducing a small amount of Ru, Ru may act as a heteroatomancy, changing the local coordination environment and growth rate during the growth of Ni-MOF, interfering with the formation of the sheet-like structure, and thus producing more wrinkles and unevenness on the material surface. As the Ru content further increases, the morphology of the material begins to change more significantly, gradually showing flower-like shapes or cluster-like structures. At this time, the characteristics of the sheet-like structure gradually become less obvious.

[0057] like Figure 2 As shown in (a) to (f), the use of different ligands in the synthesis process introduces different functional groups. Amino ligands, due to their strong coordination ability, may form stable coordination bonds with Ni and Ru, thus affecting the growth direction and final morphology of the material, resulting in a multilayered, plate-like structure. In contrast, the introduction of hydroxyl ligands may alter the surface properties and growth mechanism of the material, making it more prone to forming granular or bulk structures. This is likely related to the coordination mode and steric hindrance effect of hydroxyl ligands. Furthermore, mercapto ligands, due to their high reactivity and coordination selectivity, may form specific coordination structures with Ni and Ru during the synthesis process, leading to a uniform granular morphology.

[0058] To further investigate the effects of different ligands on the adsorption performance of the materials, Ru@Ni-MOF materials were prepared under different ligand conditions according to the parameters in Table 1, and their wettability and adsorption were analyzed. The results are as follows: Figure 3 and Figure 4 As shown.

[0059] like Figure 3 As shown in (a), the water contact angle of the Ni-MOF prepared in Comparative Example 1 is 29.44°, indicating its strong hydrophilicity. Figure 3 As shown in (b), the addition of Ru significantly increased the contact angle to 38.62°. Figure 3 As shown in (c)–(e), the introduction of thiol groups further increased the water contact angle to 43.86°, attributed to the formation of Ru-S bonds and a further reduction in surface energy. In contrast, the introduction of hydroxyl and amino groups, due to their polar properties, enhanced the hydrophilicity of the material. The surface hydrophilicity of the adsorbent did not show a significant correlation with its extraction capacity. Therefore, hydrophobic interactions are not the primary driving force of this adsorption process.

[0060] like Figure 4 As shown, Ru@Ni-MOF-NH2 maintains a positive charge under low pH conditions, while materials modified with hydroxyl and thiol groups exhibit a stronger negative charge under alkaline pH conditions through deprotonation. Ru@Ni-MOF materials can adsorb sulfonamide antibiotics via electrostatic interactions under acidic pH conditions, while forming hydrogen bonds with fluoroquinolone drugs under neutral to alkaline pH conditions. Therefore, hydrogen bonding is the primary driving force.

[0061] like Figure 5 As shown, the Ni-MOF prepared in Comparative Example 1 has an average pore size of 16.34 nm and a pore volume of 0.24 cm³. 3 ·g -1 The surface area of ​​BET is 61.45m². 2 ·g-1 The Ru@Ni-MOF prepared in Example 1 has an average pore size of 16.62 nm and a pore size of 0.23 cm. 3 ·g -1 The surface area of ​​BET is 52.33 m². 2 ·g -1 The Ru@Ni-MOF-SH has an average pore size of 23.09 nm and a pore volume of 0.39 cm³. 3 ·g -1 The surface area of ​​BET is 71.07m². 2 ·g -1 The average pore size of Ru@Ni-MOF-SH is 12.99 nm, and the pore size is 0.17 cm. 3 ·g -1 The surface area of ​​BET is 507.92 m². 2 ·g -1 The average pore size of Ru@Ni-MOF-NH2 is 14.68 nm, and the pore size is 0.19 cm. 3 ·g -1 The surface area of ​​BET is 49.41m². 2 ·g -1 The five materials are composed of numerous mesopores ranging from 2 nm to 50 nm.

[0062] Therefore, the Ru@Ni-MOF materials prepared by introducing ligands with different functional groups could not significantly improve the adsorption performance. In the following experiments, terephthalic acid was selected as the ligand to prepare Ru@Ni-MOF materials with different Ru doping amounts.

[0063] This study systematically analyzed the adsorption kinetics and mechanisms of four target veterinary drugs on Ru@Ni-MOF materials prepared under different Ru doping conditions. Furthermore, it explored the effect of Ru@Ni-MOF-solid-phase microextraction probes prepared from Ru@Ni-MOF materials on the extraction of these four target veterinary drugs. Sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin were selected as target veterinary drugs. Ru@Ni-MOF materials prepared under different Ru doping levels were used as adsorbents for adsorption, with Ni-MOF materials prepared in Comparative Examples 1 and 2 serving as comparisons. Specific adsorption experiments are as follows: Add 5 mg of adsorbent to 10 mL (20 mg L). -1 The sample solution was then centrifuged at 10,000 rpm for 5 minutes, and the supernatant was sent to a UPLC-UV instrument for analysis; the results are as follows. Figure 5 and Figure 6 As shown.

[0064] like Figure 6As shown, when Ru is undoped, there is no significant difference in adsorption performance between Ni-MOF materials synthesized by ultrasonication and hydrothermal methods. As the Ru content gradually increases, the performance of Ru@Ni-MOF gradually improves. However, when the molar amount of Ru in Ru@Ni-MOF exceeds one-fifth of that of Ni, the adsorption performance of Ru@Ni-MOF begins to gradually decrease. This may be because excessive Ru nanoparticles clog the gaps between nanosheets, reducing the specific surface area and active sites, thus decreasing adsorption performance. Therefore, a molar ratio of Ni to Ru of 10:1 was chosen as the optimal molar ratio for preparing Ru@Ni-MOF materials.

[0065] It should be noted that the Ru@Ni-MOF material prepared with a Ni to Ru molar ratio of 10:1 adsorbs sulfachlorpyridazine and is denoted as Ru@Ni-MOF-SCP; adsorbs phthalimidethiazole and is denoted as Ru@Ni-MOF-PST; adsorbs enrofloxacin and is denoted as Ru@Ni-MOF-ENR; and adsorbs norfloxacin and is denoted as Ru@Ni-MOF-NOR.

[0066] Figure 7(a) to (c) show the three characteristic peaks corresponding to O1s, Ni2p and Ru3p. After adsorption of enrofloxacin, sulfachlorpyridazine, norfloxacin, and phthalimidethiazide, the binding energies of Ni-O-Ru bonds changed from 856.4 eV to 856.47 eV, 856.53 eV, 856.36 eV, and 856.17 eV, respectively; the binding energies of Ni-O-Ni bonds changed from 874.25 eV to 874.28 eV, 874.31 eV, 874.15 eV, and 873.97 eV, respectively; the binding energies of Ru-Ru bonds changed from 462.09 eV to 462.03 eV, 462.29 eV, 461.85 eV, and 462.06 eV, respectively; and the binding energies of Ru-O bonds changed from 464.07 eV to 464.85 eV, 464.4 eV, 464.2 eV, and 464.03 eV, respectively. Based on the above results, the adsorption of enrofloxacin may be due to the carboxyl group coordinating with the Ni-O-Ru site of Ru@Ni-MOF to form a stable Ni-OC=O or Ru-OC=O bond, leading to an increase in the oxidation state of Ru (a significant increase in the binding energy of the Ru-O bond). Electrons flow from the Ni-O-Ru bond to the target material, initiating local oxidation of Ni and Ru. During the adsorption of norfloxacin, the fluorine atom attracts electrons through strong electronegativity, leading to an increase in the electron density of the Ru-Ru bond (a decrease in binding energy). Possible weak coordination (such as van der Waals forces or hydrogen bonds) has little effect on the Ni-O-Ni bond. During the adsorption of sulfachlorpyridazine, the S or N atom of the sulfanilamide group coordinates with Ru to form a Ru-S / N bond, enhancing interfacial electron transfer and leading to an increase in the oxidation state of Ru (an increase in the binding energy of the Ru-Ru bond). During the coordination process, the electron density of the Ni-O-Ru bond further decreases. During the adsorption of phthalimidethiazol, the amino group may bind to the MOF framework through hydrogen bonds, affecting the local electron distribution.

[0067] Figure 8Molecular docking simulations of four target compounds and Ru@Ni-MOF were observed, suggesting that the sulfonamide group in the sulfachlorpyridazine molecule may coordinate with the metal sites (such as Ni or Ru) of Ru@Ni-MOF. Furthermore, the aromatic ring in the molecule may interact with the MOF framework through π-π stacking interactions. The figure shows numerous contact points between the molecule and the MOF framework, indicating that adsorption may be achieved through the synergistic action of multiple forces. The sulfonamide group and aromatic ring in the phthalimide-thiazole molecule may undergo similar coordination and π-π stacking interactions with the MOF framework. Additionally, the thiazole ring in the molecule may bind to the porous structure of the MOF through hydrophobic interactions. The figure shows a relatively tight binding between the molecule and the MOF framework, indicating strong adsorption. The carboxyl group and quinolone ring in the enrofloxacin molecule may coordinate with the metal sites of the MOF. Simultaneously, the aromatic ring in the molecule may bind to the MOF framework through π-π stacking interactions. The figure shows that the contact points between the molecule and the MOF skeleton are relatively uniformly distributed, indicating that the adsorption may involve multiple interactions; the carboxyl group and quinolone ring in the norfloxacin molecule may also coordinate with the metal site of the MOF. In addition, the aromatic ring in the molecule may bind to the MOF skeleton through π-π stacking. The figure shows that the molecule and the MOF skeleton are relatively tightly bound, indicating that the adsorption is strong. In summary, Ru@Ni-MOF shows superior extraction ability to the four analytes; XPS and nitrogen adsorption-desorption experiments and molecular docking simulation results indicate that the possible extraction mechanism of Ru@Ni-MOF for the four veterinary drugs is the following synergistic effect: (1) Different target substances interact with Ru@Ni-MOF through specific chemical bonds, such as coordination bonds, hydrogen bonds, and π-π interactions, resulting in directional changes in the oxidation state and electron density of the metal center (Ni, Ru). The differences in binding energy shifts reflect the diversity of adsorption mechanisms: strong chemisorption (such as enrofloxacin and sulfachlorpyridazine) significantly alters the electronic state of interfacial bonds, making it suitable for highly selective capture; weak interactions (such as norfloxacin and phthalimidethiazide) rely more on physisorption and require functionalization modifications to enhance binding force. (2) The oxidation state and electron density of (Ni, Ru) undergo directional changes; Ru@Ni-MOF, composed of mesoporous (2-50 nm) structures, allows for easy access to analytes.

[0068] Example 3 A method for preparing a Ru@Ni-MOF solid-phase microextraction probe is basically the same as that in Example 1, except that the electrospinning conditions are different, as detailed in Table 2.

[0069] Table 2 Parameter optimization conditions for electrospinning Note: "Electrospinning solution ratio" refers to the ratio of Ru@Ni-MOF material, polyacrylonitrile, and DMF. "Mass percentage of Ru@Ni-MOF material" refers to the percentage of the mass of Ru@Ni-MOF material to the total mass of Ru@Ni-MOF material and polyacrylonitrile.

[0070] To investigate the effect of the composition of the electrospinning solution on the extraction of four target veterinary drugs using Ru@Ni-MOF-solid-phase microextraction probes, corresponding Ru@Ni-MOF-solid-phase microextraction probes were prepared according to the optimized parameters in Table 2. Sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin were selected as target veterinary drugs. The extraction efficiency of the corresponding Ru@Ni-MOF-solid-phase microextraction probes was evaluated, and the results are shown in Table 2. Figure 7 Figures (a) and (b).

[0071] like Figure 9 As shown in Figure (a), the optimal adsorption performance was observed when the ratio of Ru@Ni-MOF material, polyacrylonitrile, and DMF was 150 mg: 150 mg: 3 mL. This ratio demonstrates that it facilitates the formation of more effective adsorption sites on the Ru@Ni-MOF coating.

[0072] Conversely, when the amount of Ru@Ni-MOF material added is too low, the surface coating of the stainless steel rod becomes weak, mainly due to the low viscosity of the electrospinning solution components. Conversely, excessive addition of Ru@Ni-MOF material hinders diffusion pathways and reduces the effective specific surface area of ​​the surface coating. Therefore, a ratio of 150 mg:150 mg:3 mL of Ru@Ni-MOF material, polyacrylonitrile, and DMF was selected as the optimal electrospinning solution ratio for preparing the Ru@Ni-MOF-solid-phase microextraction probe.

[0073] like Figure 9 As shown in Figure (b), the extraction capacity of the Ru@Ni-MOF-solid-phase microextraction probe for four veterinary drugs significantly improved as the electrospinning time increased from 20 min to 40 min. However, extending the electrospinning time further to over 50 min did not significantly improve the extraction capacity, which may be because the excessively thick surface coating hindered the diffusion pathway and slowed down the adsorption kinetics. Therefore, an electrospinning time of 40 min was selected as the optimal electrospinning time for preparing the Ru@Ni-MOF-solid-phase microextraction probe.

[0074] Example 4 The Ru@Ni-MOF solid-phase microextraction probe from Example 1 was used for veterinary drug residue detection. The initial conditions were: 10 mL sample solution volume, no salt added, stirring speed of 1500 rpm, extraction at room temperature, adsorption time of 1 hour, and desorption solvent of methanol for 1 hour. The solid-phase microextraction probe program was optimized using the following methods:

[0075] Optimization of sample solution conditions.

[0076] To investigate the effect of sample solution volume on the extraction efficiency of Ru@Ni-MOF coating, 1 mL of stock solutions of sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin were added to a 250 mL volumetric flask and diluted with water to prepare sample solutions. Sample solution volumes of 5 mL, 7 mL, 9 mL, 12 mL, and 15 mL were selected, and the absolute recoveries of the Ru@Ni-MOF solid-phase microextraction probe for different sample solution volumes were tested. The results are shown below. Figure 9 As shown in Figure (c). Due to the strong turbulence effect, the diffusion rate of the target veterinary drug is relatively fast. Theoretically, a smaller sample solution volume can improve the extraction efficiency, but the extraction efficiency observed at sample volumes of 12 mL and 15 mL is comparable, as shown in Figure (c). Figure 9 As shown in Figure (c), a sample solution volume of 12 mL was chosen for subsequent experiments.

[0077] Optimization of salt concentration conditions.

[0078] To investigate the effect of NaCl concentration on the adsorption of Ru@Ni-MOF coating, 1 mL of stock solutions of sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin were added to a 250 mL volumetric flask and diluted to volume with water to prepare sample solutions. These sample solutions were then divided into three portions, and different amounts of NaCl were added to each portion to adjust the NaCl concentration to 0 wt%, 20 wt%, and 40 wt%. The absolute recoveries of the corresponding sample solutions at different NaCl concentrations were tested, and the results are shown below. Figure 9 The results are shown in Figure (d). The results show that increasing the NaCl concentration from 0 wt% to 40 wt% improved the adsorption capacity of the four veterinary drugs. This indicates that higher ionic strength has a positive effect on analyte adsorption; therefore, a NaCl concentration of 40 wt% was chosen for subsequent experiments.

[0079] Optimization of stirring rate conditions.

[0080] To investigate the effect of stirring speed on extraction efficiency, 1 mL of stock solutions of sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin were added to a 250 mL volumetric flask and diluted to volume with water to prepare sample solutions. The absolute recoveries of the corresponding sample solutions were tested at stirring speeds of 0 rpm, 600 rpm, 900 rpm, 1200 rpm, and 1500 rpm. The results are shown below. Figure 9 As shown in Figure (e), the results indicate that the extraction efficiency of the Ru@Ni-MOF solid-phase microextraction probe for the four veterinary drugs improved as the stirring speed increased from 0 rpm to 1200 rpm. However, further increases in stirring speed led to eddy currents, preventing the Ru@Ni-MOF coating from being fully submerged and thus reducing extraction efficiency. Therefore, in subsequent experiments, the optimal stirring speed was selected as 1200 rpm.

[0081] Optimization of extraction temperature conditions.

[0082] To investigate the effect of adsorption temperature on the extraction efficiency of Ru@Ni-MOF coatings, adsorption temperatures of 20℃, 40℃, and 60℃ were selected, and the absolute recovery rates of the corresponding sample solutions at different adsorption temperatures were tested. The results are as follows: Figure 9 As shown in Figure (f), the results indicate that increasing temperature leads to a gradual increase in the recovery rates of enrofloxacin, norfloxacin, and sulfathiazole. This is because the adsorption process for these three target compounds is endothermic, and increasing the temperature promotes adsorption. Conversely, for sulfachlorpyridazine, the adsorption process is exothermic, and increasing the temperature has an adverse effect on adsorption. After comprehensive consideration, 60℃ was selected as the optimal extraction temperature.

[0083] Optimization of extraction time conditions.

[0084] To investigate the effect of extraction time on the extraction efficiency of Ru@Ni-MOF coatings, extraction times of 5 min, 10 min, 20 min, 30 min, 40 min, 60 min, and 90 min were selected, and the absolute recovery rates of the corresponding sample solutions at different extraction times were tested. The results are as follows: Figure 9 The results are shown in Figure (g). Solid-phase microextraction is an equilibrium-driven process, typically reaching adsorption equilibrium within a certain time. The results showed that equilibrium was reached after 40 minutes of adsorption, and no further increase in adsorption efficiency was observed with prolonged adsorption time. Therefore, the optimal extraction time was selected as 40 minutes.

[0085] Conditional optimization of desorption parameters.

[0086] To investigate the effects of different desorption solvents and desorption times on extraction efficiency, methanol, acetonitrile, and dichloromethane were selected as desorption solvents. The absolute recoveries of the corresponding sample solutions under different desorption solvents were tested, and the results are shown below. Figure 9The results are shown in the (h) diagram. The results indicate that methanol exhibits the highest desorption efficiency among the tested desorption solvents; therefore, methanol was selected as the optimal desorption solvent.

[0087] The selected desorption times were 5 min, 10 min, 20 min, 30 min, 40 min, 60 min, and 90 min, and the absolute recovery rates of the corresponding sample solutions at different desorption times were tested. The results are as follows: Figure 9 As shown in Figure (i), the results indicate that 30 minutes is sufficient to achieve the maximum desorption of the target analyte. Therefore, the optimal desorption time is 30 minutes.

[0088] Example 5 The reusability of the Ru@Ni-MOF-solid-phase microextraction probe from Example 1 was tested under the optimized conditions of Example 3, as follows: Four target veterinary drugs were desorbed for 30 min and 60 min, and the mass of the target compound in the second desorption was compared with the mass desorbed in the first 30 min. The residual rate was quantified, and the results are as follows: Figure 10 As shown in Figure (a), the results indicate that desorption with 200 µL of methanol for 30 min is sufficient to desorb most of the analytes onto the Ru@Ni-MOF solid-phase microextraction probe.

[0089] The absolute recoveries of four target veterinary drugs were analyzed using the Ru@Ni-MOF solid-phase microextraction probe after 10 to 200 adsorption and desorption cycles, and trend bar charts of extraction efficiency were plotted. The results are as follows: Figure 10 As shown in Figure (b). Figure 10 Figure (b) verifies the extraction efficiency trend of the four target veterinary drugs over 200 cycles, indicating that the extraction efficiency decreased slightly by the 200th cycle, but the Ru@Ni-MOF-solid phase microextraction probe could still effectively extract the target analytes, demonstrating excellent reusability.

[0090] Further reproducibility tests were performed on Ru@Ni-MOF solid-phase microextraction probes prepared in the same and different batches, including intra-batch and inter-batch reproducibility tests. The results are as follows: Figure 10 As shown in Figure (c), 1, 2, and 3 are three solid-phase microextraction probes from the same batch; 4, 5, and 6 are three solid-phase microextraction probes from three different batches. The results show that within the same batch, the relative standard deviation of reproducibility remained below 9.3%, indicating stable performance of the Ru@Ni-MOF solid-phase microextraction probes. Similarly, the relative standard deviation between different batches also remained below 10.9%, indicating equally good reproducibility across different batches.

[0091] Example 6 The extraction performance of the Ru@Ni-MOF-solid-phase microextraction probe from Example 1 was tested using the optimized conditions of Example 3, as detailed below: Four commercial solid-phase microextraction (SPE) probes were selected and purchased from Merck China. These four commercial SPE probes were coated with: polydimethylsiloxane / divinylbenzene SPE probe (PDMS / DVB); polydimethylsiloxane SPE probe (PDMS); polydimethylsiloxane / carboxyl / divinylbenzene SPE probe (PDMS / CAR / DVB); and polyacrylate SPE probe (PA).

[0092] Under optimal extraction and desorption conditions, the Ru@Ni-MOF solid-phase microextraction probe was compared with four commercial microextraction probes, and the results are as follows: Figure 10 As shown in (d). Among them, 1 is Ru@Ni-MOF solid-phase microextraction probe; 2 is PDMS / DVB solid-phase microextraction probe; 3 is PDMS solid-phase microextraction probe; 4 is PDMS / CAR / DVB solid-phase microextraction probe; and 5 is PA solid-phase microextraction probe.

[0093] Depend on Figure 10 (d) The results show that the extraction efficiency of the Ru@Ni-MOF-solid-phase microextraction probe is much higher than that of commercially available solid-phase microextraction probes. Compared with commercially available solid-phase microextraction probes, the Ru@Ni-MOF-solid-phase microextraction probe of Example 1 of this invention exhibits excellent extraction ability and selectivity for four target analytes.

[0094] Example 7 The method verification of the Ru@Ni-MOF-solid-phase microextraction probe in Example 1 is as follows: Matrix effects are unavoidable in analytical assays and can affect the accuracy and precision of the method. Matrix effects are assessed by comparing the slopes of calibration curves for actual samples and calibration solutions. The matrix effect is calculated using the formula: ME = K1 / K2 × 100%; where ME is the matrix effect; K1 is the mass of antibiotics adsorbed by the Ru@Ni-MOF-solid-phase microextraction probe from spiked animal-derived agricultural product samples; and K2 is the mass of antibiotics adsorbed by the Ru@Ni-MOF-solid-phase microextraction probe from veterinary antibiotic standard solutions. ME values ​​between 80% and 120% indicate slight signal inhibition or enhancement; values ​​below 80% or above 120% indicate significant signal inhibition or enhancement. The matrix effects of the three target analytes in milk and pork were below 80% (see Tables 3 and 4), demonstrating that matrix effects have a significant impact on analyte detection.

[0095] High-performance liquid chromatography, or HPLC-UV for short. The Ru@Ni-MOF solid-phase microextraction probe from Example 1 was combined with HPLC-UV for the analysis of target analytes. The target analytes were sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin.

[0096] The validation results of the Ru@Ni-MOF-solid phase microextraction probe-HPLC-UV method on milk and pork samples are shown in Tables 3 and 4.

[0097] Table 3 Results of Milk Matrix Matching Calibration Strategy Table 4 Results of Pork Matrix Matching Calibration Strategy The results showed that the correlation coefficients of the four target analytes were all greater than 0.9945. The detection limits for milk samples ranged from 0.02 μg / L to 0.03 μg / L, with a signal-to-noise ratio of 3. Intra-day precision ranged from 4.8% to 7.5%, and inter-day precision ranged from 6.5% to 9.2%.

[0098] The detection limit for pork samples ranged from 0.0 μg / L to 0.07 μg / L. The intra-day accuracy ranged from 7.6% to 8.9%, and the inter-day accuracy ranged from 8.6% to 11.2%.

[0099] Therefore, the method of combining Ru@Ni-MOF-solid phase microextraction probe with HPLC-UV shows excellent performance in the quantitative analysis of target analytes in milk and pork samples, exhibiting high sensitivity, high precision and high selectivity.

[0100] Example 8 The feasibility test of the high-performance liquid chromatograph is as follows: The detection conditions for high performance liquid chromatography are as follows: Ultrapure water with a resistivity of 18.25 MΩ·cm, sourced from an ultrapure water system, was purchased from Chengdu Yinghang Water Treatment Equipment Co., Ltd. The four target analytes were enrofloxacin, norfloxacin, sulfachlorpyridazine, and phthalimidethiazide. 50 mg of each analyte was dissolved in 50 mL of methanol and stored at 4 °C. The stock solutions were diluted with ultrapure water to obtain sample solutions of each analyte at a concentration of 100 μg / L. The feasibility of simultaneously detecting sulfachlorpyridazine, phthalimidethiazide, enrofloxacin, and norfloxacin using ultra-high performance liquid chromatography (UHPLC) was studied.

[0101] Chromatographic conditions: ZORBAX SB-C18 column, 5 Particle size: 150 mm × 4.6 mm inner diameter; mobile phase: acetonitrile and 0.2% formic acid aqueous solution; flow rate: 1 mL / min; sample volume: 20 mL / min. L, column temperature 30℃, detection wavelength 225nm. In the gradient elution program, the concentration of acetonitrile was increased from 5% to 20% within 0 min to 14 min, and then increased from 20% to 45% within 14 min to 28 min. After holding for 1 min, the concentration of acetonitrile was rapidly reduced to 5% within 1 min, and then held at equilibrium for 2 min.

[0102] Example 9 Sample analysis was performed using the optimized conditions of Example 3 and the Ru@Ni-MOF-solid-phase microextraction probe of Example 1. The specific sample analysis process is as follows: Preparation of milk samples: 1 g of zinc sulfate and 1 g of K4[Fe(CN)6]·3H2O were added to 100 mL of milk. The mixture was vortexed for 20 seconds, and then centrifuged at 10,000 rpm for 3 minutes to remove the precipitate. This process was repeated six times until the residue was negligible. The resulting supernatant was finally filtered through a 0.22 μm membrane and stored in a refrigerator at 4 °C. Then, 10 mL of the filtrate obtained above was taken, and the Ru@Ni-MOF-solid phase microextraction probe from Example 1 was immersed in it to enrich four veterinary drugs. The extraction temperature was room temperature, the stirring speed was 1200 rpm, and the enrichment time was 40 min. The Ru@Ni-MOF-solid phase microextraction probe was then immersed in a sample vial containing 200 μL of methanol solution at room temperature for static desorption for 30 min. Finally, the analysis was performed according to the ultra-high performance liquid chromatography conditions of Example 7.

[0103] Example 10 Sample analysis was performed using the optimized conditions of Example 3 and the Ru@Ni-MOF-solid-phase microextraction probe of Example 1. The specific sample analysis process is as follows: Preparation of pork samples: Use fresh or frozen pork, remove visible fat, and mix the meat thoroughly to obtain a pork sample. Weigh 10g of the pork sample into a 250mL centrifuge tube and add 50mL of acetonitrile. Vortex the mixture at 2000rpm for 1 minute to disperse the extract, then homogenize at 10000rpm for 10 minutes. Transfer the solution to a 250mL separating funnel and add 100mL of n-hexane. Shake the mixture thoroughly for 5 minutes and let it stand until it separates into layers, then collect the lower layer. Transfer this solution to a 10mL centrifuge tube, centrifuge several times, and then dry it under nitrogen at 40℃. Dissolve the residue in 1.0mL of an initial mobile phase consisting of an aqueous solution of formic acid containing 20% ​​acetonitrile, and filter through a 0.22μm organic membrane. Store the pretreated sample in a refrigerator at 4℃.

[0104] Before analysis, all samples were filtered through an organic membrane with a pore size of 0.22 μm. Then, 10 mL of the filtrate was taken, and the Ru@Ni-MOF-solid-phase microextraction probe was immersed in it to enrich four target veterinary drugs. The extraction temperature was room temperature, the stirring speed was 1200 rpm, and the extraction time was 40 min. Then, the Ru@Ni-MOF-solid-phase microextraction probe was immersed in a sample vial containing 200 μL of methanol at room temperature for static desorption for 30 min. Finally, the analysis was performed according to the ultra-high performance liquid chromatography conditions in Example 7.

[0105] The sample analysis results for Examples 9 and 10 are as follows: Since the target analyte was not initially detected in the sample, it was spiked at three concentration levels. According to GB 31650-2021 and GB 31650.1-2022 standards, the residue limits for enrofloxacin, sulfachlorpyridazine, and phthalimidethiazole in beef, pig, and sheep muscle and milk are 100 μg / kg. According to GB 31650.1, the residue limit for norfloxacin in beef, pig, and sheep muscle and milk is 2 μg / kg. Therefore, the spiking levels for enrofloxacin, sulfachlorpyridazine, and phthalimidethiazole were set at 50 μg / kg, 100 μg / kg, and 200 μg / kg; the spiking levels for norfloxacin were set at 1 μg / kg, 2 μg / kg, and 5 μg / kg.

[0106] Table 5. Spiking concentrations and recoveries of different target analytes in milk and pork. Table 5 shows that the recoveries for milk samples ranged from 87.8% to 102.3%, with relative standard deviations (RSDs) between 5.9% and 9.7%. Similarly, the recoveries for pork samples ranged from 82.7% to 100.8%, with RSDs between 7.2% and 10.5%. These results demonstrate that the Ru@Ni-MOF-solid-phase microextraction probe-HPLC-UV method exhibits good accuracy and precision in the detection and quantification of target compounds in complex food samples.

[0107] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Ru@Ni-MOF material, characterized in that, Includes the following steps: Using Ni-MOF as a matrix, a solvothermal method was used to partially dope Ni-MOF to introduce metal nodes Ru. Two-dimensional Ru@Ni-MOF nanosheets with Ni-O-Ru coordination bonds were synthesized with the assistance of nickel foam, thus obtaining Ru@Ni-MOF material. The molar ratio of Ni to Ru in Ru@Ni-MOF materials is 50:1 to 50.

2. The method for preparing Ru@Ni-MOF material according to claim 1, characterized in that, The specific preparation method of the Ru@Ni-MOF material is as follows: In a solvent system, ligands, Ni source and Ru source are mixed and nickel foam is added. The mixture is then subjected to a solvothermal reaction at 120℃~160℃ to synthesize two-dimensional Ru@Ni-MOF nanosheets with Ni-O-Ru coordination bonds with the assistance of nickel foam, thus obtaining Ru@Ni-MOF material. The molar ratio of ligand, Ni source and Ru source is 50:50:1 to 50.

3. The method for preparing Ru@Ni-MOF material according to claim 2, characterized in that, The ligands are terephthalic acid, 2,5-dihydroxyterephthalic acid, p-mercaptoterephthalic acid, or 2-aminoterephthalic acid.

4. The method for preparing Ru@Ni-MOF material according to claim 2, characterized in that, The solvothermal reaction time is 10h to 14h.

5. A Ru@Ni-MOF material, characterized in that, The Ru@Ni-MOF material is prepared by the method for preparing Ru@Ni-MOF material according to any one of claims 1 to 4.

6. A solid-phase microextraction probe, characterized in that, The invention includes a substrate and an extraction coating. The extraction coating is made from Ru@Ni-MOF material. In a solvent system, Ru@Ni-MOF material and polyacrylonitrile are mixed and then the extraction coating is formed on the surface of the substrate by electrospinning. The mixture is then immersed in ethanol and dried to obtain the final product. The Ru@Ni-MOF material is the Ru@Ni-MOF material described in claim 5.

7. The solid-phase microextraction probe according to claim 6, characterized in that, The ratio of Ru@Ni-MOF material, polyacrylonitrile, and solvent is 75–225 mg: 75–225 mg: 3 mL.

8. The solid-phase microextraction probe according to claim 6, characterized in that, The thickness of the extraction coating is 100μm to 140μm, and the length is 0.8cm to 1.2cm; The base is a stainless steel rod.

9. The application of the solid-phase microextraction probe according to claim 6 in veterinary drug detection, characterized in that, The veterinary drug is at least one of enrofloxacin, norfloxacin, sulfachlorpyridazine, and phthalimidethiazide.

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