Preparation And Adsorption Of Cephalexin Magnetic Molecularly Imprinted Polymers

Cefalexin（CFL）is one of the most widely used cephalosporin antibiotics in China which has made great contributions to the treatment of animal diseases and improved quality of animal products,but at the same time its residual problems also have a negative impact on human health,the ecological environment and certain microorganisms.Therefore,it is very important to establish a rapid,accurate and simple method for detecting the trace CFL in food of animal origin.Magnetic nanoparticles（MNPs）are a new type of intelligent functional nanomaterials,which can rapidly separate the target under the external magnetic field after being a certain surface modified.Molecular imprinting technology（MIT）is a technique that aims at specific template molecule and it is used to prepare the high-molecular polymers with a high affinity and specific recognition capabilities.In this paper,the magnetic nano-molecularly imprinted polymers（MMIPs）with high selectivity and excellent stability to cephalexin were prepared through combining MNPs and MIT,and they were applied in rapid separation and enrichment of trace cefalexin in complex matrices.The main contents and results of the study are listed as follows:1、MNPs with good monodispersity were prepared through co-precipitation and the surface was modified with silane coupling agent.And the MMIPs were synthesized on the surface of modified Fe₃O₄MNPs using cefalexin as the template molecule through suspension polymerization and by investigating the factors that affected the synthesis of polymers,we got the optimal preparation conditions were that the functional monomer was acrylamide（AM）,the cross-linking agent was ethylene glycol dimethacrylate（EGDMA）,the solvent was acetonitrile,cefalexin was 1 mmoL,AM was 4 mmoL,EGDMA and azodiisobutyronitrile（AIBN）were respectively 20mmoL and 0.12 mmoL,and acetonitrile was 100 mL.2、The morphology,structure,crystal form and magnetic property of the polymer were characterized with scanning electron microscopy（SEM）,Fourier transform infrared spectrometer（FT-IR）,X-ray diffraction（XRD）,and vibrating sample magnetometer（VSM）.It was observed that the shape of the microspheres was regular with an average diameter of approximately 220⁶80 nm,the holistic structure was loose.The spinel-structured Fe₃O₄ existed in the particles synthesized in each step and the modification and polymerization process didn’t transform the crystal structure.The saturation magnetization of MNPs and MMIPs was 49.851 emu/g and 5.936emu/g,respectively.3、Adsorption kinetics,adsorption thermodynamics and adsorption selectivity experiments were carried out on polymers and the mechanism of recognition and imprint were studied through the pseudo-first-order and pseudo-second-order kinetic models,the Scatchard model and the imprinting and separation factor.The results showed that the adsorption capacity of CFL on MMIPs increased rapidly in the first30 minutes and the adsorption equilibrium time was about 60 minutes.The kinetic model fitting showed that the adsorption of CFL on the polymers conformed to the pseudo-second-order kinetic model,so that the chemical adsorption was the rate-limiting step;Adsorption thermodynamics and Scatchard analysis showed that the adsorption capacity of CFL on MMIPs was higher than that on non-imprinted polymers（MNIPs）.And there were two binding sites in the MMIPs.The equilibrium dissociation constant and observed amount of adsorption of high affinity sites were respectively 0.997mg/L and 18.466 mg/g while they were respectively 3.268 mg/L and 45.259 mg/g of low affinity sites.However,there was an equivalent binding site in the MNIPs which showed a uniform affinity for CFL and the equilibrium dissociation constant and observed amount of adsorption were respectively 23.776mg/L and 21.929 mg/g;Adsorption selectivity experiments indicated that the MMIPs showed a specific adsorption capacity for CFL in presence of template molecular structure analogues and non-analogues.The imprinting factor of MMIPs was above 2and the separation factor of MMIPs was significantly higher than that of MNIPs.4、The prepared MMIPs were used as an extractant for pretreatment of three kinds of standard samples and showed a good accuracy,precision and stability combined with high performance liquid chromatography（HPLC）.The recovery rates of cefalexin in tap water,pork and milk respectively ranged from 88.68%to 94.80%,87.30%to 92.45%,87.58%to 95.13%and the corresponding relative standard deviations（RSD）ranged from 1.26%to 1.26%,1.17%to 1.86%and 1.71%¹.86%.RSD of three samples was less than 3.58%within 24 h and less than 4.34%in the day.The obtained limit of detection（LOD）for this method of tap water was 0.01 mg/kg and of pork and milk were both 0.005 mg/kg.MMIPs showed a good separation and enrichment ability compared with unextraction and extracting with MNIPs.