An LDH molecularly imprinted hydrogel composite material, its preparation method and application

Abstract

The present invention relates to the field of chloramphenicol detection, and particularly to a LDH molecularly imprinted hydrogel composite material, its preparation method and application. In the present invention, α-bromoisobutyric acid is inserted into the LDH interlayer through 2 to 3 times of anion exchange to obtain a novel initiator LDH-Br; then, cyclodextrin is fully reacted with triethylamine and methacryloyl chloride (MA), centrifuged, the supernatant is collected, and an excessive amount of acetonitrile is added for recrystallization to precipitate, the precipitate is collected, and after drying, a methacryloyl chloride-modified cyclodextrin polymer is prepared as a functional monomer, etc. The composite material LDH-CD-MIP for the analysis of residual chloramphenicol in environmental water samples and foods has high adsorption capacity and satisfactory selectivity. Therefore, the method established by the present invention has strong specificity and high sensitivity, and shows good application potential in actual environmental water treatment and food inspection.

Description

Technical Field

[0001] The present invention relates to the field of chloramphenicol detection, and particularly to an LDH molecularly imprinted hydrogel composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of China's economy and the increasing improvement of people's living standards, people pay more attention to the safety issues of food and the environment. The problems of drug residues and pesticide residues in food are one of the important issues of food hygiene and safety. Chloramphenicol is a broad-spectrum antibacterial antibiotic. It is the first choice for the treatment of typhoid and paratyphoid, and is one of the effective drugs for the treatment of anaerobic infections. Secondly, it is also used for the treatment of various infectious diseases caused by sensitive microorganisms. It is in the form of white or colorless needle-shaped or flaky crystals, with a melting point of 149.7 - 150.7 °C, and its properties are extremely stable. Its aqueous solution does not lose efficacy even after boiling for 5 hours. On October 27, 2017, the International Agency for Research on Cancer of the World Health Organization released a preliminary list of carcinogens for reference. Chloramphenicol is in the list of Group 2A carcinogens.

[0003] Toxicological studies have shown that chloramphenicol can inhibit the synthesis of mitochondrial proteins in bone marrow cells, and has toxic effects on human and animal bone marrow cells and liver cells. It can cause aplastic anemia, accompanied by leukopenia and thrombocytopenia, gray baby syndrome in newborns and premature infants, etc. It can also induce the drug resistance of pathogenic bacteria, seriously threatening human health. Nowadays, its serious adverse reactions have led to less and less clinical use. In food applications, the European Union, the United States, China and other countries strictly prohibit the use of such drugs in food animals. However, due to their low price and good antibacterial effect, many illegal vendors still use them illegally. In order to protect the health of the general public and safeguard the export trade of China's animal-derived foods, the research on the detection methods of chloramphenicol compounds is one of the hottest topics in maintaining current food safety.

[0004] In order to effectively detect and control chloramphenicol in edible animal products, the country has invested a large amount of human and material resources in researching and formulating detection methods for chloramphenicol drug residues in foods and water samples, mainly including microbiological methods, high performance liquid chromatography, immunoassay, gas chromatography, high performance liquid chromatography-tandem mass spectrometry, etc. The following is a brief introduction to the current chloramphenicol residue detection methods: Microbiological detection technology has the characteristics of being easy to operate, economical and simple, and can detect various antibiotic drugs. However, it has relatively low specificity and sensitivity, is not suitable for large-scale detection, and will produce false positive results, leading to misjudgment. At the same time, in recent years, various analytical methods combined with various instrument devices have emerged continuously, promoting the chromatographic detection technology to have better detection and analysis capabilities. It has the advantages of high accuracy and high sensitivity. However, when dealing with pre-sample processing, due to the high cost, strong professionalism and complex operation, it is not suitable for rapid large-scale detection. Spectral detection technology mainly conducts quantitative and qualitative analysis by forming characteristic spectra of substances. It has the characteristics of low cost and convenient operation. However, it has low selectivity, and the near-infrared spectroscopy detection method needs to be reasonably combined with chemometric techniques in order to achieve the purpose of decomposing data, which is highly professional and not suitable for daily rapid large-scale detection. Immunoassay technology is mainly an analytical method based on the specific binding behavior of antigens and antibodies. Among them, radioimmunoassay has relatively high sensitivity. However, this technology has problems such as radioactive pollution and short isotope half-life, which will affect people's health and the environment to a certain extent.

[0005] Molecularly imprinted polymers (MIPs) are a separation technology based on molecular recognition. The synthesized molecularly imprinted compounds have specific recognition ability for target molecules and can selectively recognize target compounds from complex samples. Therefore, they have attracted much attention in the field of analytical detection. In the enrichment detection of chloramphenicol residues in environmental water samples and foods, MIPs can be used as the first choice for capturing and enriching small molecule pollutants due to their advantages such as predictable structure, specific recognition characteristics, low preparation cost, stable properties, and reusability. However, in actual extraction applications, MIPs also have some problems, such as weak specific recognition ability, incomplete elution of imprinted molecules, and the common small molecule halide initiators are easily affected by branching points and steric hindrance. Therefore, in view of the possible large amounts of residues of CAP in environmental water samples and foods at present, there is an urgent need to establish a sensitive, rapid and reliable method for the detection and analysis of residual CAP in environmental water samples and foods to ensure people's physical health and the safety of China's food trade. Summary of the Invention

[0006] To solve the above problems, the present invention provides an LDH molecularly imprinted hydrogel composite material, a preparation method and an application thereof. The composite material LDH-CD-MIP synthesized by the present invention for the analysis of residual chloramphenicol in environmental water samples and foods has high adsorption capacity and satisfactory selectivity. Therefore, the method established by the present invention has strong specificity and high sensitivity, and shows good application potential in actual environmental water treatment and food inspection.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of an LDH molecularly imprinted hydrogel composite material, comprising the following steps:

[0009] 1) Mix an ethylenediaminetetraacetic acid solution with a zinc nitrate solution and an aluminum nitrate solution to obtain a mixed solution. After adjusting the pH value of the mixed solution to be alkaline, carry out a reaction, wash and dry the obtained precipitate to obtain LDH-EDTA;

[0010] 2) Mix the LDH-EDTA obtained in step 1) with an α-bromoisobutyric acid solution and carry out an ion exchange reaction to obtain LDH-Br;

[0011] 3) Pre-assemble methylacryloyl chloride-modified cyclodextrin and chloramphenicol to obtain a pre-assembled product;

[0012] 4) React the pre-assembled product obtained in step 3) with methacrylic acid to obtain a reaction product;

[0013] 5) React the reaction product obtained in step 4) with ethylene glycol dimethacrylate and the LDH-Br obtained in step 2) to obtain a gel;

[0014] 6) Wash and dry the gel obtained in step 5) to obtain an LDH molecularly imprinted hydrogel composite material.

[0015] Preferably, in step 1), the concentration of the ethylenediaminetetraacetic acid solution is 0.2 - 1.5 mol / ml;

[0016] the concentration of the zinc nitrate solution is 0.2 - 1.5 mol / ml;

[0017] the concentration of the aluminum nitrate solution is 0.2 - 1.5 mol / ml;

[0018] the volume ratio of the ethylenediaminetetraacetic acid solution to the mixed salt solution of the zinc nitrate solution and the aluminum nitrate solution is 1:(1 - 3).

[0019] Preferably, the reaction conditions in step 1) include: the water bath temperature is 10 - 100 °C, the water bath time is 8 - 96 h, and nitrogen protection;

[0020] The drying temperature is 50 to 200 °C and the time is 2 to 48 h.

[0021] Preferably, the mass ratio of LDH-EDTA to the volume of the α-bromoisobutyric acid solution in step 2) is 1 g:(20 - 80) ml;

[0022] The concentration of the α-bromoisobutyric acid solution is 0.01 to 0.2 mol / ml;

[0023] The conditions of the ion exchange reaction include: the temperature is 20 to 30 °C and the time is 10 to 100 h.

[0024] Preferably, the preparation method of the methacryloyl chloride-modified cyclodextrin in step 3) includes the following steps:

[0025] a. Mix cyclodextrin with N,N-dimethylformamide, triethylamine, and methacryloyl chloride and react at 30 to 200 °C for 10 to 100 min, then centrifuge to obtain the supernatant;

[0026] The mass ratio of cyclodextrin to the volume of N,N-dimethylformamide, the volume of triethylamine, and the volume of methacryloyl chloride is 1 - 30 g:5 - 100 ml:5 - 100 ml:5 - 100 ml;

[0027] b. Crystallize the obtained supernatant with excessive acetonitrile, and dry the obtained precipitate at 20 to 100 °C for 2 to 10 h to obtain the methacryloyl chloride-modified cyclodextrin.

[0028] Preferably, the molar ratio of the methacryloyl chloride-modified cyclodextrin to chloramphenicol in step 3) is 1 - 15:1;

[0029] The conditions of the pre-assembly include: stirring at 20 to 30 °C for 10 to 50 min.

[0030] Preferably, the molar ratio of the pre-assembled product to methacrylic acid in step 4) is (1 - 4):1;

[0031] The conditions of the reaction include: the temperature is 20 to 50 °C and the time is 10 to 100 min.

[0032] Preferably, the molar ratio of ethylene glycol dimethacrylate to the mass of LDH-Br in step 5) is (5 - 20) ml:1 g;

[0033] The conditions of the reaction include: the temperature is 10 to 100 °C and the time is 8 to 72 h;

[0034] In step 6), the gel is washed with a detergent, which is methanol and an acid, and the volume ratio of methanol to the acid is 5 to 20:1, and the acid is formic acid, glacial acetic acid or phosphoric acid;

[0035] The drying conditions include: the temperature is 30 to 150 °C and the time is 2 to 48 h.

[0036] The present invention also provides an LDH molecularly imprinted hydrogel composite material prepared by the preparation method described in the above technical solution.

[0037] The present invention also provides the application of the LDH molecularly imprinted hydrogel composite material described in the above technical solution in detecting residual chloramphenicol in environmental water samples and / or foods.

[0038] The preparation method of layered double metal hydroxide (LDH) is mature and there are many types. The preparation process is simple, rapid and can be synthesized in large quantities. As an inorganic template material, it is an inorganic compound with a layered structure and is easy to be eluted with acid. Based on these characteristics of LDH, a kind of polymer initiator is synthesized by inserting α-bromoisobutyric acid into the LDH interlayer through 2 to 3 times of anion exchange, and through the intercalation protection of LDH, the subsequent initiation reaction will be more stable and complete.

[0039] At the same time, aiming at the problems of weak specific recognition ability, weak affinity and poor dispersion ability of MIP in aqueous solution, the present invention prepares MIP with methyl acryloyl chloride (MA)-modified cyclodextrin (CD) as the functional monomer, so that the target analyte can not only bind to the commonly used functional monomer methacrylic acid (MAA) through hydrogen bonds, but also synergistically with the host-guest interaction of cyclodextrin to enhance the selectivity of MIP for the target analyte. In addition, due to the structure of cyclodextrin with a hydrophilic outer cavity and a hydrophobic inner cavity, MIP can be dispersed more rapidly and uniformly in aqueous solution, greatly improving the adsorption capacity of MIP for the analyte to be measured.

[0040] In the present invention, α-bromoisobutyric acid is inserted into the interlayer of LDH through 2-3 times of anion exchange to obtain a novel initiator LDH-Br. Then, cyclodextrin reacts fully with triethylamine and methacryloyl chloride (MA), and after centrifugation, the supernatant is collected and recrystallized with excessive acetonitrile to precipitate, and the precipitate is collected and dried to obtain a methacryloyl chloride-modified cyclodextrin polymer as a functional monomer. After that, using dimethyl sulfoxide as a reaction medium, using the methacryloyl chloride-modified cyclodextrin as a functional monomer and chloramphenicol as a template molecule, pre-assembly is carried out, and then ethylene glycol dimethacrylate (EDGMA) is added dropwise as a cross-linking agent for cross-linking, and the previously prepared LDH-Br is added as an initiator to initiate the reaction, and a template-carrier complex is prepared by atom transfer radical polymerization (ATPR). Finally, the LDH-Br and the template molecule are eluted with a methanol-acetic acid mixture, and after drying, a molecularly imprinted hydrogel composite based on LDH is obtained.

[0041] The adsorption mechanism of the present invention is as follows: the host-guest inclusion of cyclodextrin synergistically with molecular imprinting for selective adsorption, thus showing high adsorption performance for chloramphenicol antibiotics.

[0042] The beneficial effects of the present invention are as follows:

[0043] The methods and results of this experiment were compared with the identification and detection of chloramphenicol in food by other materials. Although some organic materials have a large adsorption capacity, the reaction temperature is high and the reaction equilibrium time is long, which will cause certain energy consumption. Moreover, compared with other molecular imprinting characteristics, LDH-CD-MIP shows good adsorption capacity and recovery rate.

[0044] In addition, in the present invention, α-bromoisobutyric acid is intercalated into the interlayer of LDH to obtain a novel initiator LDH-Br, which solves the problem that the commonly used small molecule halide initiator is easily affected by the branching point and steric hindrance. Using methacryloyl chloride-modified cyclodextrin as a functional monomer, the target analyte can not only bind to the commonly used functional monomer methacrylic acid (MAA) through hydrogen bonds, but also through the host-guest interaction of cyclodextrin, enhancing the selectivity of MIP for the target analyte. In addition, due to the structure of cyclodextrin with a hydrophilic outer cavity and a hydrophobic inner cavity, MIP can be dispersed more rapidly and uniformly in an aqueous solution, greatly improving the adsorption capacity of MIP for the analyte to be measured. Using LDH as a substrate, the substrate is easy to wash off and provides protection for the reaction initiated by α-bromoisobutyric acid, making the reaction more stable and complete.

[0045] In summary, the LDH-CD-MIP synthesized in the present invention for the residual analysis of CAP in environmental water samples and foods provides new ideas and methods for solving the deficiencies of current MIPs in the detection field, and the synthesized composite material has high adsorption capacity and satisfactory selectivity. Therefore, the method established in the present invention has strong specificity and high sensitivity, and shows good application potential in actual environmental water treatment and food inspection. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments.

[0047] Figure 1 are TEM and SEM electron microscopes;

[0048] Figure 2 are the results of the selectivity experiment;

[0049] Figure 3 are the results of the adsorption experiment;

[0050] Figure 4 is the preparation flow chart. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] A preparation method of a LDH molecularly imprinted hydrogel composite material includes the following steps:

[0052] 1) Mix an ethylenediaminetetraacetic acid solution with a zinc nitrate solution and an aluminum nitrate solution to obtain a mixed solution. After adjusting the pH value of the mixed solution to be alkaline, carry out a reaction, wash and dry the obtained precipitate to obtain LDH-EDTA;

[0053] 2) Mix the LDH-EDTA obtained in step 1) with an α-bromoisobutyric acid solution and carry out an ion exchange reaction to obtain LDH-Br;

[0054] 3) Pre-assemble methylacryloyl chloride-modified cyclodextrin and chloramphenicol to obtain a pre-assembled product;

[0055] 4) React the pre-assembled product obtained in step 3) with methacrylic acid to obtain a reaction product;

[0056] 5) React the reaction product obtained in step 4) with ethylene glycol dimethacrylate and the LDH-Br obtained in step 2) to obtain a gel;

[0057] 6) Wash and dry the gel obtained in step 5) to obtain a LDH molecularly imprinted hydrogel composite material.

[0058] In the present invention, an ethylenediaminetetraacetic acid solution is mixed with a zinc nitrate solution and an aluminum nitrate solution to obtain a mixed solution. After adjusting the pH value of the mixed solution to be alkaline, a reaction is carried out. The obtained precipitate is washed and dried to obtain LDH-EDTA.

[0059] In the present invention, the concentration of the ethylenediaminetetraacetic acid solution is preferably 0.2 - 1.5 mol / ml; the concentration of the zinc nitrate solution is preferably 0.2 - 1.5 mol / ml; the concentration of the aluminum nitrate solution is preferably 0.2 - 1.5 mol / ml; the volume ratio of the ethylenediaminetetraacetic acid solution to the mixed salt solution of the zinc nitrate solution and the aluminum nitrate solution is preferably 1:(1 - 3). In the present invention, the conditions of the reaction preferably include: the water bath temperature is 10 - 100 °C, the water bath time is 8 - 96 h, and nitrogen protection; the drying temperature is preferably 50 - 200 °C, and the time is preferably 2 - 48 h.

[0060] In the present invention, the obtained LDH-EDTA is mixed with an α-bromoisobutyric acid solution and then an ion exchange reaction is carried out to obtain LDH-Br.

[0061] In the present invention, the mass ratio of LDH-EDTA to the volume of the α-bromoisobutyric acid solution is 2 g:100 ml; the concentration of the α-bromoisobutyric acid solution is preferably 0.01 - 0.2 mol / ml. In the present invention, the conditions of the ion exchange reaction preferably include: the temperature is 20 - 30 °C, and the time is 10 - 100 h.

[0062] In the present invention, methylacryloyl chloride-modified cyclodextrin and chloramphenicol are pre-assembled to obtain a pre-assembled product.

[0063] In the present invention, the preparation method of the methylacryloyl chloride-modified cyclodextrin preferably includes the following steps:

[0064] a. Cyclodextrin is mixed with N,N-dimethylformamide, triethylamine, and methylacryloyl chloride and reacted at 30 - 200 °C for 10 - 100 min, and then centrifuged to obtain a supernatant; the mass ratio of cyclodextrin to the volume of N,N-dimethylformamide, the volume of triethylamine, and the volume of methylacryloyl chloride is 1 - 30 g:5 - 100 ml:5 - 100 ml:5 - 100 ml; the concentration of N,N-dimethylformamide is of analytical grade;

[0065] b. The obtained supernatant is crystallized with excessive acetonitrile, and the obtained precipitate is dried at 20 - 100 °C for 2 - 10 h to obtain methylacryloyl chloride-modified cyclodextrin.

[0066] In the present invention, the molar ratio of the methylacryloyl chloride-modified cyclodextrin to chloramphenicol is preferably 1 - 15:1. In the present invention, the conditions of the pre-assembly preferably include: stirring at room temperature (25 °C) for 30 min.

[0067] The pre-assembled product obtained in the present invention is reacted with methacrylic acid to obtain a reaction product.

[0068] In the present invention, the mass ratio of the pre-assembled product to methacrylic acid is preferably 1:(0.2 - 2). In the present invention, the reaction conditions preferably include: the temperature is 20 - 50 °C, and the time is 10 - 100 min.

[0069] The reaction product obtained in the present invention is reacted with ethylene glycol dimethacrylate and LDH-Br to obtain a gel. In the present invention, the mass ratio of ethylene glycol dimethacrylate to LDH-Br is preferably (5 - 20):1. In the present invention, the reaction conditions preferably include: the temperature is 10 - 100 °C, and the time is 8 - 72 h;

[0070] The gel obtained in the present invention is washed and dried to obtain an LDH molecularly imprinted hydrogel composite material. In the present invention, the gel is washed with a detergent, and the detergent is preferably methanol and an acid. The volume ratio of methanol to the acid is preferably 5 - 20:1, and the acid is acetic acid. In the present invention, the drying conditions preferably include: the temperature is 30 - 150 °C, and the time is 2 - 48 h.

[0071] The present invention also provides an LDH molecularly imprinted hydrogel composite material prepared by the preparation method described in the above technical solution.

[0072] The present invention also provides the application of the LDH molecularly imprinted hydrogel composite material described in the above technical solution in detecting residual chloramphenicol in environmental water samples and / or foods.

[0073] To further illustrate the present invention, the present invention will be described in detail below in conjunction with examples, but they should not be construed as limiting the protection scope of the present invention.

[0074] Example 1

[0075] 1. Experimental part

[0076] 1.1 Reagents and samples

[0077] Chloramphenicol (CAP), florfenicol (FF), thiamphenicol (TAP), ciprofloxacin (CIP), norfloxacin (NOR), sulfadiazine (SFD), methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), 2,2'-bipyridine (2,2'-bpy), cuprous bromide (CuBr), dimethyl sulfoxide (DMSO), Zn(NO3)2, Al(NO3)3, methanol, acetic acid, NaOH, EDTA, α-bromoisobutyric acid, ethanol, acetonitrile, β-cyclodextrin (β-CD), N,N-dimethylformamide (DMF), and triethylamine were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Sulfathiazole (SFT) and methacryloyl chloride (MA) were purchased from Energy Chemical Co., Ltd. (Anhui, China). The above reagents were all unpurified analytical pure reagents. Formic acid (HPLC) was purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Methanol (HPLC) and acetonitrile (HPLC) were purchased from Thermo Fisher Scientific (Shanghai, China) Instrument Co., Ltd.

[0078] 1.2 Preparation of novel initiator LDH-Br

[0079] Under the condition of water bath, the mixed salt solution of zinc nitrate and aluminum nitrate was added to the EDTA solution. After the EDTA was completely dissolved, the sodium hydroxide solution was added dropwise. The dropping was stopped when a certain pH value was reached. After reacting for a period of time, the white precipitate, namely LDH-EDTA, was taken. After washing and drying, it was added to the sodium hydroxide ethanol-aqueous solution containing α-bromoisobutyric acid. After ion exchange at room temperature, the novel initiator LDH-Br was obtained.

[0080] The concentrations of the above EDTA solution, zinc nitrate solution, aluminum nitrate solution, and sodium hydroxide solution were 0.42 mol / ml, 1.32 mol / ml, 0.66 mol / ml, and 1 mol / ml, respectively. The water bath temperature was 95 °C, the pH value for stopping titration was 10.5, the drying temperature was 60 °C, the drying time was 12 h, and the ion exchange duration was 72 h.

[0081] 1.3 Preparation of functional monomer

[0082] Cyclodextrin, triethylamine, and methacryloyl chloride were placed in an N,N-dimethylformamide solution. Under nitrogen protection, it was stirred and dissolved at low temperature, gradually heated and left standing, centrifuged, and the supernatant was taken and added with an excessive amount of acetonitrile for recrystallization to form a white precipitate. The precipitate was taken, washed, and dried to obtain the functional monomer, methacryloyl chloride-modified cyclodextrin.

[0083] The above-mentioned cyclodextrins include α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, carboxymethyl-β-cyclodextrin and hydroxypropyl-β-cyclodextrin; the amounts of cyclodextrin, triethylamine solution, methacryloyl chloride solution and N,N-dimethylformamide solution are 2 g, 8 ml, 5 ml and 30 ml; the low-temperature stirring temperature is 0 °C, the temperature during heating is 30 °C, the drying temperature is 30-200 °C, and the drying duration is 1-48 h.

[0084] 1.4 Preparation of LDH-based molecularly imprinted hydrogel composite material (LDH-CD-MIP)

[0085] 6 mmol of the prepared methacryloyl chloride-modified cyclodextrin was completely dissolved in dimethyl sulfoxide solution, 1 mmol of chloramphenicol was added for pre-assembly, and then 4 mmol of methacrylic acid (MAA) was added. After the reaction was complete, atom transfer radical polymerization was used. Under nitrogen protection, crosslinking agent ethylene glycol dimethacrylate (EDGMA) was added for crosslinking for 30 min. Then, copper bromide and 2,2'-bipyridine were reacted with the novel initiator LDH-Br prepared in step 1) for 30 min. Finally, the above reaction solution was subjected to a water bath to obtain a blue hydrogel. The hydrogel was washed with a 9:1 methanol-acetic acid mixture and dried at 60 °C for 24 h to obtain an LDH-based molecularly imprinted hydrogel composite material. The synthesis method of the non-imprinted polymer is the same as the above, except that the CAP molecule is not added.

[0086] 2. Results and discussion

[0087] 2.1 Adsorption experiment

[0088] In terms of adsorption kinetics, 10 g of MIP and NIP were weighed respectively and placed in 10 mL of a mixed standard solution (50 mg / L), and oscillated for different times (5, 10, 15, 20, 30, 60, 90 min). The concentration of CAP in the supernatant (C t , mg / L) was determined by HPLC. The binding amount of CAP at different times t was defined as the adsorption amount at time (Q t , mg / g). The calculation formula is:

[0089]

[0090] where the volume of the CAP solution is expressed as V (L), and the mass of the MIP or NIP used is expressed as m (g).

[0091] For isothermal adsorption, 10 g of MIP and NIP were weighed and added to 10 mL of standard solutions with different concentrations (5, 10, 15, 30, 50, 80, 110, 140, 180, 220 mg / L) at 25 °C for 3 hours. The concentration of CAP in the supernatant (C e, mg / L). At equilibrium, the binding amount of CAP on MIP or NIP is called the equilibrium adsorption capacity (Q e , mg / L). The calculation formula is:

[0092]

[0093] Through calculation, the adsorption capacity of the molecularly imprinted composite material with LDH-CD hydrogel as the carrier is 75.44 mg / g when the initial concentration of chloramphenicol is 200 μg / ml.

[0094] 2.2 Selectivity experiment

[0095] The recognition selectivity of MIP was demonstrated by selecting two structurally related compounds, florfenicol, and four other antibiotics that may be present in the matrix (such as sulfanilamide, ciprofloxacin, norfloxacin, sulfadiazine, and sulfathiazole). The selectivity experiment was carried out in a 10 mL mixed solution containing the target compound and the competitive compound (50 mg / L) and adsorbed at 25 °C for 50 min. The concentration of the supernatant was determined by a UV-visible spectrophotometer. The imprinting factor (IFs = QLDH-CD-MIP / QLDH-CD-NIP) is an important parameter to verify the imprinting selectivity. As can be seen from the figure, 5, the binding ability of LDH-CD-MIP to the three amphenicols antibiotics is higher than that of other competitive compounds, and the IFs are 3.9, 9.43, and 6.85 respectively, indicating that LDH-CD-MAP has high selectivity for the three analytes, because the polymer synthesized in this study uses CAP as the imprinting template cavity.

[0096] 2.3 Sensitivity experiment

[0097] Take 1 g of honey and dissolve it in 10 ml of water to prepare a honey sample. Add 10 mg of LDH-CD-MIP to the sample, shake for 50 min, then centrifuge and take the LDH-CD-MIP that has adsorbed chloramphenicol. Add 8 ml of a solution with a volume ratio of 9:1 (methanol: acetic acid), shake for 30 min, centrifuge and take the supernatant, dry it, and redissolve it with 200 μl of methanol to obtain an LOD of 10 ng / ml.

[0098] 2.4 Reusability and reproducibility

[0099] Reusability is one of the most important factors to evaluate the economy of the adsorbent and should be taken seriously. The rebinding experiment was carried out in a 10 mL analyte solution with a concentration of 50 mg / L. After adsorbing for 50 min, centrifuge to take the supernatant, and determine the concentration of the supernatant by a UV-visible spectrophotometer.

[0100] The reproducibility was evaluated by synthesizing three different batches of 10 mg LDH-CD-MIP at different times. It was added to the CAP solution (10 mL, 50 mg / L) for adsorption for 50 min, and then centrifuged to obtain the supernatant, and the concentration of the supernatant was measured by an ultraviolet-visible spectrophotometer.

[0101] 2.5 Characteristics

[0102] The phase composition and crystal structure of LDH-EDTA and LDH-Br were determined by XRD. The X-ray diffraction peaks (003), (006) and (009) of LDH synthesized by the classical co-precipitation method were symmetric and sharp, proving that it has a good layered structure. In addition, according to Bragg's law, the interlayer spacings of LDH, LDH-EDTA and LDH-Br are 0.78 nm, 1.42 nm and 1.42 nm respectively. It can be considered that EDTA molecules are inserted into the LDH layer, and the interlayer structure does not change significantly after α-bromoisobutyric acid enters the interlayer.

[0103] The microscopic morphology was observed by SEM to explain the difference in adsorption capacity between them. From the SEM results, there are significant differences in the structures of the two. MIP has many irregular micropores, which may be cavities formed by template removal, and the surface is rough and uneven, which can expose more adsorption sites. Moreover, it can be seen from the figure that MIP is composed of a multi-layer structure, which can increase the adsorption capacity, while NIP has a dense and smooth surface structure, which makes it difficult for the target analyte to attach and adsorb. Therefore, NIP exhibits weak adsorption capacity.

[0104] 3. Example Applications

[0105] Under nitrogen protection and at 95 °C in a water bath, a mixed salt solution composed of 100 ml of 1.3 mol / mL zinc nitrate and 0.66 mol / mL aluminum nitrate was added to 100 ml of 0.42 mol / mL EDTA solution. After the EDTA was completely dissolved, 1 mol / ml sodium hydroxide solution was added dropwise. The addition was stopped when the pH reached 10.5. The white precipitate after reacting for 12 h was LDH-EDTA. Then it was washed until neutral, dried at 60 °C for 12 h, and 2 g of the synthesized LDH-EDTA was added to 100 ml of a 0.2 M sodium hydroxide ethanol-water (5%, v / v) solution containing 0.1 M α-bromoisobutyric acid. The reaction was carried out at room temperature, and after 3 days of ion exchange, a new initiator LDH-Br was obtained. 2 g of β-cyclodextrin was stirred and dissolved in 30 ml of DMF, and 8 ml of triethylamine was added under N2 protection. Then 5 ml of MA was added to the above reaction system with a syringe, and a light yellow triethylamine salt was precipitated. After the addition of MA was complete, the temperature was gradually raised to 30 °C and the reaction was carried out for 60 minutes. Then the supernatant was centrifuged, an excessive amount of acetonitrile was added, and a white precipitate was precipitated. The precipitate was collected by centrifugation, recrystallized from acetonitrile 3 times, and dried at 60 °C for 6 h. The final white powder was β-cyclodextrin modified with methacryloyl chloride (β-CD-MA). 300 mg of the prepared methacryloyl chloride modified cyclodextrin was completely dissolved in 50 ml of dimethyl sulfoxide solution, 1 mmol of chloramphenicol was added for pre-assembly, and then 4 mmol of methacrylic acid (MAA) was added. After the reaction was complete, by atom transfer radical polymerization, under nitrogen protection, a cross-linking agent ethylene glycol dimethacrylate (EDGMA) was added for cross-linking for 30 min, and then copper bromide and 2,2'-bipyridine and the prepared new initiator LDH-Br were added to the above reaction system and reacted for 30 min. Finally, the above reaction solution was placed in a water bath at 70 °C for 24 h to obtain a blue hydrogel. The hydrogel was washed with a methanol-acetic acid (9:1, v / v) solution and dried at 60 °C for 24 h to obtain an LDH-based molecularly imprinted hydrogel composite material.

[0106] Take 1 g of honey and dissolve it in 10 ml of water to prepare a honey sample. Add 10 mg of LDH-CD-MIP to the sample, shake for 50 min, then centrifuge and take the LDH-CD-MIP adsorbed with chloramphenicol. Add 8 ml of 9:1 (methanol:acetic acid) solution, shake for 30 min, centrifuge and take the supernatant. After drying, it was redissolved with 200 μl of methanol to obtain an LOD of 10 ng / ml.

[0107] Take 4 ml of milk and add 10 ml of acetonitrile to precipitate the protein in the milk. Centrifuge to collect the supernatant, dry it at 40 °C, then add 10 ml of water and vortex for 30 min. Add 10 mg of LDH-CD-MIP to the sample, shake for 50 min, then centrifuge to obtain the LDH-CD-MIP adsorbed with chloramphenicol. Add 8 ml of a 9:1 (methanol: acetic acid) solution, shake for 30 min, centrifuge to take the supernatant, dry it, and redissolve it with 200 μl of methanol to obtain an LOD of 10 ng / ml.

[0108] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of an LDH molecularly imprinted hydrogel composite material, characterized in that, It includes the following steps: 1) Mix an ethylenediaminetetraacetic acid solution with a zinc nitrate solution and an aluminum nitrate solution to obtain a mixed solution. After adjusting the pH value of the mixed solution to be alkaline, carry out a reaction. Wash and dry the obtained precipitate to obtain LDH-EDTA; LDH is a layered double metal hydroxide; 2) Mix the LDH-EDTA obtained in step 1) with an α-bromoisobutyric acid solution and carry out an ion exchange reaction to obtain LDH-Br; 3) Pre-assemble methacryloyl chloride-modified cyclodextrin and chloramphenicol to obtain a pre-assembled product; The preparation method of the methacryloyl chloride-modified cyclodextrin includes the following steps: a. Mix cyclodextrin with N,N-dimethylformamide, triethylamine, and methacryloyl chloride and react at 30-200 °C for 10-100 min, and centrifuge to obtain a supernatant; The mass ratio of the cyclodextrin to the volumes of N,N-dimethylformamide, triethylamine, and methacryloyl chloride is 1-30 g:5-100 mL:5-100 mL:5-100 mL; b. Crystallize the obtained supernatant with excessive acetonitrile, and dry the obtained precipitate at 20-100 °C for 2-10 h to obtain methacryloyl chloride-modified cyclodextrin; 4) React the pre-assembled product obtained in step 3) with methacrylic acid to obtain a reaction product; the reaction conditions include: the temperature is 20-50 °C and the time is 10-100 min; 5) React the reaction product obtained in step 4) with a cross-linking agent ethylene glycol dimethacrylate and the initiator LDH-Br obtained in step 2) by atom transfer radical polymerization to obtain a gel; 6) Wash and dry the gel obtained in step 5) to obtain an LDH molecularly imprinted hydrogel composite material; wash the gel with a detergent, the detergent is methanol and an acid, and the volume ratio of the methanol to the acid is (5-20):1, and the acid is formic acid, glacial acetic acid or phosphoric acid.

2. The preparation method according to claim 1, characterized in that, In step 1), the concentration of the ethylenediaminetetraacetic acid solution is 0.2-1.5 mol / mL; The concentration of the zinc nitrate solution is 0.2-1.5 mol / mL; The concentration of the aluminum nitrate solution is 0.2-1.5 mol / mL; The volume ratio of the ethylenediaminetetraacetic acid solution to the mixed salt solution of the zinc nitrate solution and the aluminum nitrate solution is 1:(1-3).

3. The preparation method according to claim 1, characterized in that, In step 1), the reaction conditions include: the water bath temperature is 10-100 °C, the water bath time is 8-96 h, and nitrogen protection; In step 1), the drying temperature is 50-200 °C and the time is 2-48 h.

4. The preparation method according to claim 1, characterized in that, In step 2), the mass ratio of the LDH-EDTA to the volume of the α-bromoisobutyric acid solution is 1 g:(20-80) mL; The concentration of the α-bromoisobutyric acid solution is 0.01-0.2 mol / mL; The ion exchange reaction conditions include: the temperature is 20-30 °C and the time is 10-100 h.

5. The preparation method according to claim 1, characterized in that, In step 3), the molar ratio of the methacryloyl chloride-modified cyclodextrin to chloramphenicol is (1-15):1; The pre-assembly conditions include: stirring at 20-30 °C for 10-50 min.

6. The preparation method according to claim 1, characterized in that, In step 4), the molar ratio of the pre-assembly to methacrylic acid is (1-4):

1.

7. The preparation method according to claim 1, characterized in that, In step 5), the molar amount of ethylene glycol dimethacrylate to the mass of LDH-Br is 5-20 mol:1 g; In step 5), the reaction conditions include: temperature is 10-100 °C, and time is 8-72 h; In step 6), the drying conditions include: temperature is 30-150 °C, and time is 2-48 h.

8. An LDH molecularly imprinted hydrogel composite material prepared by the preparation method according to any one of claims 1-7.

9. Use of the LDH molecularly imprinted hydrogel composite material according to claim 8 for detecting residual chloramphenicol in environmental water samples.

10. Use of the LDH molecularly imprinted hydrogel composite material according to claim 8 for detecting residual chloramphenicol in foods.

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