Membrane Protected Covalent Organic Framework LZU1 To Extract Estrogens From Milk

Estrone(E1),17?-estradiol(E2)and estriol(E3)are endogenous estrogens,which are abused in livestock industry because they can promote animal growth,increase milk yield and so on.These estrogens can enter the human body through the food chain,leading to precocious puberty,reproductive dysfunction and other diseases.Milk,as one of the most important foods in daily life,is an important source of human exposure to estrogens.Therefore,its safety detection is of great significance for human healthy diet.However,milk matrix is complex and estrogens exists as trace components in milk,so preconcentration treatment is needed before detection.Adsorbent is an important factor affecting the extraction efficiency.Covalent organic frameworks(COFs),as a new type of crystalline porous polymer,have the advantages of large specific surface area,good stability and porosity.Which makes it a great potential as an efficient adsorbent.In this work,E1,E2 and E3 were the research objects.Membrane protection direct immersion solid-phase microextraction(SPME)fibers and magnetic solid phase extraction(MSPE)adsorbents were prepared based on COF-LZU1 to establish two pretreatment method,and combined with GC-FID and HPLC-FLD for enrichment and detection of three estrogens in milk.The main research contents and results are as follows:(1)Stainless steel wire was coated with COF-LZU1 through Nafion to rapidly prepare SPME fiber(COF-LZU1/Nafion).Using dialysis membrane with a molecular weight cutoff to protect the fiber and established membrane protection direct immersion solid-phase microextraction(MP-DI-SPSME)method,and combined with GC-FID to detect E2 in milk.Scanning electron microscopy(SEM),thermogravimetric analysis(TGA),N₂ adsorption,Fourier transform infrared spectroscopy(FT-IR)and X-ray diffraction(XRD)were used to characterize the COF-LZU1 and the home-made COF-LZU1/Nafion fiber.The extraction and derivatization conditions were optimized to establish a method for the determination of E2.The limit of detection(LOD,S/N=3)and quantification(LOQ,S/N=10)of the method were 0.8?g/L and 2.5?g/L,respectively.The relative standard deviations(RSD)of intra-day,inter-day and fiber to fiber were 5.3%,7.7%and 8.3%,respectively.The extraction efficiency of the COF-LZU1/Nafion fiber was still above 90%after repeated use of 160 times.Compared with other fibers,the extraction efficiency of E2 with the COF-LZU1/Nafion fiber was 22.1,8.4,3.6times higher than that of bare stainless steel wire,PDMS/DVB and PDMS,respectively.Three levels(30,100 and 500?g/L)of spiked experiments were carried out,and the recoveries were77.3%?108.2%with RSD less than 9.7%.(2)Fe₃O₄ magnetic nanomaterials were synthesized by solvothermal method.Magnetic composite(Fe₃O₄@COF-LZU1)was prepared by in-situ growth of COF-LZU1 on the Fe₃O₄surface.The Fe₃O₄@COF-LZU1 was used as magnetic adsorbent to establish the membrane protection MSPE method and combined with HPLC-FLD for enrichment and detection of E1,E2 and E3.The Fe₃O₄@COF-LZU1 were characterized by XRD,FT-IR,Transmission electron microscopy(TEM),Vibrating sample magnetometer(VSM),Energy dispersive X-ray spectroscopy(EDX)and N₂ adsorption.The extraction and desorption conditions were optimized,and the recycling performance of the adsorbent was measured.In addition,the adsorption kinetics was studied,and the adsorption mechanism was also preliminary explored.The LODs and LOQs of the method were 0.01?0.15?g/L and 0.06?0.80?g/L,respectively.The intra assay,inter assay and medial precisions were less than 7.3%,9.1%and 7.1%,respectively.The extraction efficiency of the Fe₃O₄@COF-LZU1 was still above 90%after repeated use for 10 times.The adsorption behavior conforms to the pseudo-second order kinetics and belongs to chemical adsorption.There are hydrogen bonds and?-?conjugation between the Fe₃O₄@COF-LZU1 and three analytes.The recoveries of three levels(10,50 and100?g/L)were 77.3%?112.1%with RSDs less than 9.0%.In this study,we found that COF-LZU1 has high extraction efficiency for three estrogens,and the dialysis membrane can effectively retain macromolecular substances such as protein outside the membrane,greatly reducing matrix interference.The two established methods are environmentally friendly and have good repeatability and reproducibility,and have been successfully applied to the enrichment and detection of three estrogens in milk.Which provides an effective and versatile method for the enrichment and detection of analytes in complex matrix samples.