Preapartion Of Magnetic Molecularly Imprinted Polymer For Selectively Enriching Auxin Indolebutyric Acid And Naphthylacetic Acid

Auxin can regulate the growth and development of plants, has been widely applied into agriculture to modify the growth cycle and improve yields of crop. Due to the toxicity of auxin, it could be harmful to human health while intaking with food. To strengthen the food safety management, the content of auxin shold be determined before coming into market. However the high aboudant of substrates in plant tissue would interefere the analysis of auxin, especially when in low content, it is necessary to develop appropriate sample pretreatment method to remove thses interefering substrats before analysis. In this work, three types of magnetic molecularly imprinted polymers(MMIPs) with core-shell or multi-hollow structure were prepared for fast and specific enrichment of indolebutyric acid(IBA) or naphthylacetic acid(NAA), two most popularly used auxin.(1) Preparation of IBA- MMIPs with core-shell structureFe3O4 microspheres were firstly prepared via a one-pot hydrothermal process. After coated with a Si O2 layer with St?ber method, methacryloxy propyl trimethoxyl silane was added to derivarize C=C bond on the surface of beads. And then, MMIPs was prepared with IBA as template molecule, the methyl acrylic acid as functional monomer and Fe3O4 as magnetic component, ethylene glycol dimethacrylate as crosslinking agent, 2,2’-Azobisisobutyronitrile as initiator, and chloroform as solvent. The morphological, size and polymeric characteristics of MMIPs were characterized by scanning electron microscope(SEM), transmission electron microscope(TEM) and fourier transform infrared spectroscopy(FT-IR). Monodisperse solid microspheres were obtained. The results of adsorption isotherms of IBA and Scatchard analysis revealed that there were two types of affinity binding sites. The apparent maximum binding capacity(Qmax) and dissociation content(Kd) were 3.47 mg/g and 15.63 μg/m L for high affinity binding sites, and 2.78 mg/g and 5.49 μg/m L for low affinity binding sites, respectively. The adsorption of IBA onto MMIPs was matched the pseudo-second-order kinetic model(R2=0.9949), which meant the adsorption rate was controlled mainly by chemical adsorption. Recoveries of 49.33%-66.89% with a relative standard deviation(RSD) less than 4.56% were obtained for IBA spiked at three concentration levels in blank and tomato juice samples.(2) Preparation of IBA-MMIPs with multi-hollow structure(IBA-M-MMIPs)A simple strategy was developed for the preparation of IBA-M-MMIPs by incorporating IBA and Fe3O4 magnetic fluid simultaneously into a poly(styrene-co-methacrylic acid) copolymer matrix. The as prepared absorbents were characterized using SEM, TEM FT-IR and mercury porosimeter. The results of adsorption isotherms of IBA and Scatchard analysis revealed that there existed two types of affinity binding sites in the absorbents. The apparent maximum binding capacity and dissociation content were 17.88 mg/g and 158.70 μg/m L for high affinity binding sites, and 9.31 mg/g and 35.04 μg/m L for low affinity binding sites, respectively. The results of adsorption kinetics study testified that IBA-M-MMIPs possessed excellent recognition capacity and fast kinetic binding behavior to the objective molecules due to the high specifici surface area as large as 511.30 m2/g. The pseudo-second-order kinetic model provides a good correlation(R2=0.9926) for the adsorption of IBA onto IBA-M-MMIPs in contrast to the pseudo-?rst-order model(R2=0.9794), which meant that the adsorption rate was controlled mainly by chemical adsorption. Recoveries of 75.54-87.92% with RSD less than 2.94% were obtained for IBA spiked at three concentration levels in pear samples.(3) Preparation of NAA-MMIPs with multi-hollow structure(NAA-M-MMIPs)The preparation of NAA-M-MMIPs was used the same procedure of preparing IBA-M-MIPs except using NAA as template. The as prepared NAA-M-MMIPs were characterized using SEM, TEM FT-IR. The results of adsorption isotherms of NAA and Scatchard analysis revealed that there existed two types of affinity binding sites in the absorbents. The apparent maximum binding capacity and dissociation content were 29.37 mg/g and 161.29 μg/m L for high affinity binding sites, and 19.50 mg/g and-128.21 μg/m L for low affinity binding sites, respectively. The results of adsorption kinetics study testified the pseudo-second-order kinetic model provides a good correlation(R2=0.9543) for the adsorption of NAA onto NAA-M-MMIPs in contrast to the pseudo-?rst-order model(R2=0.9162). The adsorption rate was controlled mainly by chemical adsorption through sharing electrons between the template molecules and the sorbent. Recoveries of 78.73-89.23% with RSD less than 3.94% were obtained for NAA spiked at three concentration levels in blank and tomato juice samples.