Application Of Magnetic Molecularly Imprinted Polymer Combined With High Performance Liquid Chromatography In Determination Of Pesticide Residues In Chinese Medicinal Materials

Traditional Chinese medicine is widely used in the treatment of diseases and health maintenance,but the problem of pesticide residues is the hidden danger of its safe use.High performance liquid chromatography（HPLC）is common method for pesticide residue analysis.However,due to its complex substrate and low pesticide content,Chinese medicinal materials often pretreated before pesticide residue detection.In order to reduce the interference of complex matrix on analyte detection results and improve the detection accuracy of the instrument,magnetic molecular imprinting technology was used to rapidly and selectively separate and enrich target molecules from samples.Specific research contents are as follows:（1）Taking Fe₃O₄as the core,the structure of Fe₃O₄was modified to prepare the magnetic carrier Fe₃O₄@SiO₂-MPS.Using diazinon as template,methacrylic acid and hydroxyethyl methacrylate as functional monomers,ethylene glycol dimethacrylate and azodiisobutyronitrile as cross-linking agent and initiator respectively,and methanol and acetonitrile as pore-making agent in a volume ratio of 1 to 4,the molecularimprinted layer was prepared.The magnetic molecularly imprinted polymer with high saturation magnetization and special recognition ability was prepared by grafting the traditional molecularly imprinted polymer onto the surface of magnetic material Fe₃O₄@SiO₂-MPS using surface molecularly imprinted technology.Fourier transform infrared spectroscopy and other characterization methods were used to analyze the structure of the material,and its adsorption performance was studied.The results showed that the polymer could selectively adsorb the target molecule,and the adsorption of the target molecule was close to equilibrium within 20 min,and the maximum adsorption capacity was 7.46mg/mg.The recovery rate was 89.5%after six adsorption desorption cycles.The method was applied to the determination of diazinon in Angelica sinensis,and the content of diazinon was 0.107 mg/kg,which was lower than the national limit of 0.5 mg/kg.Under the optimum conditions,limit of detection（LOD）=13.44×10^-3mg/m L,limit of quantitation（LOQ）=44.80×10^-3mg/m L.The results show that this method has great advantages for the determination of diazinon in complex matrix,and can be used for the separation,enrichment and detection of diazinon in natural products and traditional Chinese medicine.（2）Using Fe₃O₄@SiO₂as a carrier to modify it,one method is to continue the use of Fe₃O₄@SiO₂-MPS,the other is to introduce multi-walled carbon nanotube on the basis of Fe₃O₄@SiO₂.The molecular imprinted layer was prepared by using the two materials as substrate,thiabendazole as template,methacrylic acid as functional monomer,ethylene glycol dimethacrylate and azodiisobutyronitrile as cross-linking agent and initiator,respectively,toluene and acetonitrile as pore-forming agent at a volume ratio of 1 to 3.The results show that the total adsorption capacity of MIPs increases with the introduction of CNTs,but the if value of magnetic CNTs-MIP is far less than that of Fe₃O₄@SiO₂-MPS-MIP.In terms of reusability,the adsorption rate of Fe₃O₄@SiO₂-MPS-MIP after six times of adsorption-desorption（93.1%）was significantly higher than that of magnetic carbon nanotube imprinted polymer（80.3%）,and the former had better reusability.Therefore,it is not significant to introduce molecular imprinting technology into carbon nanotubes for the specific adsorption of trace components in complex matrix,while Fe₃O₄@SiO₂-MPS-MIP is more suitable for the extraction of trace components in complex matrix.In addition to the specific adsorption performance,the adsorbent prepared on the basis of Fe₃O₄@SiO₂-MPS has good reusable performance,can be reused for many times,and can reduce the cost of detection,and is economical.