Synthesis Of Functional Magnetic Microspheres By Surface Photo-Initiated Polymerization For Selective Extraction Of Veterinary Drug Residues From Milk Samples

Photo- initiated free radical polymerization can lead to continuous polymerization of monomers for the preparation of the novel block polymer. The functional magnetic microspheres were prepared by photo-initiated free radical polymerization for the rapid purification of sample matrix and the selective enrichment of analytes. A new method was established for the determination of fluoroquinolones and chloramphenicols residues in milk samples by magnetic dispersion solid-phase extraction(MD-SPE)- high performance liquid chromatography(HPLC).Chapter 1: The preparation methods of magnetic microspheres were reviewed. The preparation method and application of molecularly imprinted magnetic microspheres were introduced. The research progresses of the functionalized magnetic microspheres and MD-SPE technology were presented.Chapter 2: A novel method for the preparation of the metal coordination imprinted magnetic microspheres was developed using photo- initiated free radical polymerization on the surface of magnetic microspheres. The magnetic nanoparticles was coated with silica gel, modified with amino group, grafted with the chloromethyl groups by substitution reaction between amino groups on surface of magnetic microspheres and acyl chloride groups of 4-(chloromethyl)benzoyl chloride(CMBC). Subsequently, the iniferter groups were introduced by reacting the microsphere-bound the chloromethyl groups with sodium diethyldithiocarbamatre(DDCT). Enrofloxacin-Co(II) coordination imprinted layer was synthesized on the surface of magnetic microspheres through photo-initiated free radical polymerization using enrofloxacin-Co(II) as the template molecule, itaconic acid as the functional monomers, ethylene glycol dimethacrylate as the cross-linker, iniferter as the initiator in methanol solvent. Morphology characteristics and grafting rate were characterized by TEM, FT-IR and TG. The adsorption capacity and selectivity of magnetic microspheres as the adsorbent was investigated by static adsorption and competitive adsorption experiments. The results showed that the adsorbent had better dispersion, selectivity and higher adsorption capacity. Under the optimum extraction conditions, the magnetic microspheres were used as a sorbent for magnetic dispersion solid-phase extraction of fluoroquinolones(FQs) antibiotics from milk samples. The average recoveries of three FQs were obtained in the range of 89.6%-100.8%. The limits of detection and quantitation of the milk samples wer e in the range of 1.18-2.05 ?g kg-1 and 3.94-6.82 ?g kg-1, respectively.Chapter 3: A series of magnetic composite microspheres(MCMs) were prepared by the surface-initiated radical polymerization. The Fe3O4/PAM, Fe3O4/PITA, Fe3O4/PMAA and Fe3O4/PMMA were prepared using acrylamide(AM), methacrylic acid(MAA), itaconic acid(ITA) and methyl methacrylate(MMA) as the functional monomers, respectively. Based on the living characteristics of iniferter, the block polymer layer on the surface of magnetic composite microspheres(Fe3O4/P(MMA-co-ITA)) was prepared by continuous photo-initiated free radical polymerization between Fe3O4/PMMA with itaconic acid monomer. The MCMs were characterized by TEM, FT-IR and TG and indicated that the polymer layer has successfully covered the Fe3O4 nanoparticles. It can be observed by TEM that the MCMs are core- shell structure microspheres with the average diameters around 230 nm and the coating thickness in the range of 15-20 nm. The contact angle of the Fe3O4/PMMA is about 108 degree and the Fe3O4/P(MMA-co-ITA) is about 82 degree, which showed that the outer surface of magnetic composite microspheres had better hydrophilicity and the inner layer had better hydrophobicity, this is a typical characteristics of restricted access materials. The results showed that the proposed method was an effective method for preparation of different characteristics of block polymer layer on the surface of magnetic microspheres by photo-initiated free radical polymerization.Chapter 4: A novel restricted access media- molecularly imprinted magnetic microsphere(RAM-MIMM) was prepared by initiator- transfer agent- terminator(iniferter) method. The iniferter was synthesized through the magnetic nanoparticles were coated with silica- gel, modified with amino-group and reaction with 4-(chloromethyl)benzoyl chloride and sodium diethyldithiocarbamate. The molecularly imprinted magnetic microsphere(MIMM) was prepared using florfenicol(FF) as the template, itaconic acid(ITA) as the functional monomer, ethylene glycol dimethacrylate as the cross- linker, iniferter as surface initiator in anhydrous ethanol solvent. The hydrophilic external layer of the MIMM was formed by iniferter polymerization using glycidyl methacrylate(GMA) as monomer, and t hen the hydrolysis of the linear poly(GMA). The obtained RAM-MIMMs were characterized by TEM, TG, FT-IR and adsorption experiments. The Fe3O4 magnetic microspheres were demonstrated with the average diameters around 230 nm and the coating thickness in the range of 20-30 nm. The RAM-MIMMs exhibited high selectivity(1.68) of the imprinted cavities and hydrophilicity of the external surface with water compatibility and exclusion biomacromolecules. The RAM-MIMMs were used for magnetic dispersion extraction of FF from milk samples. The average recoveries were obtained in the range of 85.4-94.7% with precision 2.95-4.97%. The limits of detection and quantitation of the proposed method were in the range of 4.40-18.31 ?g kg-1 and 14.66-61.02 ?g kg-1, respectively. The proposed method was successfully applied to fast clean-up and selective enrichment of florfenicol in milk.