Synthesis Of Functional Magnetic Molecularly Imprinted Polymer And Its Application In Complex Food Detection

Magnetic molecularly imprinted polymers（MMIPs）can selectively recognize target molecules.It has the advantages of recognition specificity,high efficiency selectivity and reusability.It can effectively remove matrix interference.It is suitable for the detection and analysis of trace substances in complex samples.MMIPs has attracted extensive attention in sample pretreatment and analytical applications.In this paper,several functionalized MMIPs were synthesized using surface molecular imprinting techniques based on Fe₃O₄as a magnetic nanocore.The MMIPs were used as solid-phase extractants in combination with high performance liquid chromatography for the specific,sensitive and efficient detection of genistein,rosmarinic acid and zearalenone in complex food samples.The main study and results of this paper are as follows:（1）Synthesis of vinyl functional dye lignin magnetic molecularly imprinted polymer and its application in soy sauce samplesIn this section,a new method of genistein separation based on genistein magnetic molecularly imprinted polymers（Gen-MMIPs）was developed using Fe₃O₄as a carrier,genistein as a template molecule,andγ-methacryloxypropyltrimethoxysilane（MPS）as a vinyl modifier using surface molecular imprinting technology.The morphological characterization（TEM）by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）showed that the Gen-MMIPs have a diameter of about500 nm and a three-dimensional structure on the surface.The saturation magnetization of Gen-MMIPs was 24.79 emu/g measured by vibrating sample magnetometer（VSM）,which confirmed its excellent magnetic separation performance.Fourier transform infrared spectroscopy（FT-IR）showed that the functional groups were successfully modified on the surface of the magnetic carrier.It was verified that Gen-MMIPs had a good porous structure by nitrogen adsorption desorption test.The specific surface area was 207.145 m²/g and the average pore diameter was about 8.03 nm.Different levels of different preparation conditions were optimized using single-factor tests to obtain the best performing Gen-MMIPs.Adsorption experiments showed that the adsorption capacity of Gen-MMIPs was 5.81mg/g,and the adsorption equilibrium was reached within 20 min.The first-order and second-order kinetic models were used to fit the correlation coefficient with the experimental data of adsorption kinetics of Gen-MMIPs.The second-order kinetic model R²was greater than 0.99,indicating that the adsorption process of polymer on genistein had both chemical adsorption and physical adsorption.The fitting results of Scatchard equation show that there are two binding sites with different affinity on the surface of Gen-MMIPs,which is also confirmed by the high fitting degree of Freundlich model（R²>0.99）.Genistein in soy sauce samples was selectively separated by Gen-MMIPs as a pretreatment method combined with high performance liquid chromatography.The recovery was 85.7%-88.5%,and the relative standard deviation was 2.1%-3.0%（<5%）,which proved that this method can be used for the purification and detection of genistein in actual samples.（2）Preparation of virtual template zearalenone molecularly imprinted polymers and their applicationsZearalenone magnetic molecularly imprinted polymers were synthesized using curcumin as an alternative template.SEM,TEM and FT-IR characterization and adsorption experiments were used to demonstrate that the polymers have specific recognition sites.VSM technology proves that the polymer can be quickly separated under magnetic field without cumbersome centrifugation or filtration.Combined with the excellent adsorption equilibrium time of the polymer,the whole extraction process is only 20 min（adsorption and separation）.The analysis of the isothermal adsorption results of ZEN-MMIPs showed that the adsorption process followed the Langmuir and Freundlich isothermal adsorption model,and the fitting results of the Skachard equation confirmed that ZEN-MMIPs had two affinity sites for ZEN.The experimental results also showed that ZEN-MMIPs exhibited good structural stability of adsorption-desorption and could be reused more than 10 times,which greatly reduced the cost of use.Zen-MMIPs-HPLC detection can effectively eliminate the interference of miscellaneous peaks in the chromatogram of spiked corn juice and complete the purification and enrichment of Zen in complex samples.Alternative template technology can effectively eliminate the interference caused by the leakage of template molecules in chromatographic analysis.Calculated by peak area normalization method,the concentration of Zen in spiked real samples increased from24.3%（before Zen MMIPs treatment）to 80.1%（after Zen MMIPs treatment）.The detection limit and quantitative limit were 0.45 mg/L and 1.5 mg/L respectively.The intra day,intra day,inter batch and intra batch precision were less than 8%.It is proved that the method can be used for the trace residue analysis of zearalenone in practical samples.（3）Synthesis and application of magnetic rosmarinic acid sandwich structure molecularly imprinted polymer based on metal organic framework MOF-5 materialFirstly,taking amino modified Fe₃O₄particles as the core,the magnetic MOF carrier material was prepared by carboxyl dehydration reaction between the carboxyl group on the surface of MOF-5 and the amino group on the surface of Fe₃O₄.Then,molecularly imprinted polymers were synthesized on the surface of magnetic MOF substrate with rosmarinic acid as template molecule,acrylamide（AM）as functional monomer,azodiisobutyronitrile（AIBN）as initiator and ethylene glycol dimethacrylate（EGDMA）as crosslinking agent.The sandwich structure of Fe3O4-MOF-MIPs was formed.The existence of sandwich structure was confirmed by SEM,TEM,XRD and FTIR.The magnetic properties and adsorption capacity were investigated by VSM tests and adsorption experiments,and the experimental results demonstrated that this polymer combines the superparamagnetism of Fe₃O₄,the high specific surface area of MOF materials and the specificity of MIPs.The fitting correlation coefficient R²of Freundlich and Langmuir models for Fe₃O₄-MOF-MIPs adsorption experimental data is greater than 0.95,which proves that the two models can describe the isothermal adsorption experimental process.The fitting results of first-order and second-order kinetic models show that the adsorption process has both chemical adsorption and physical adsorption.Different levels of different preparation conditions were optimized by single factor test.The maximum adsorption capacity Qmax of Fe₃O₄-MOF-MIPs is 9.6 mg/g.The separation and determination of rosmarinic acid in actual samples of perilla and purple cabbage were realized by high performance liquid chromatography.The recovery was 88.1～107.8%,the relative standard deviation was 1.6～4.4%（<5%）,the detection limit and quantitative limit were 0.35 mg/L and 1.10 mg/L respectively.The intra day,intra day,inter batch and intra batch precision were less than 7%.It is proved that the method can be used for the separation and determination of rosmarinic acid in complex practical samples.