| This paper aims to study the preparation and properties of two new(-)-epigallocatechin gallate(EGCG) surface molecularly imprinted polymers which were employed as affinity adsorbents of solid-phase extraction for the separation and purification of EGCG from tea polyphenols as well as to indentify trace amount of EGCG in toothpaste samples. A new method based on surface molecularly imprinted polymer-solid phase extraction-high performance liquid chromatography analysis has been established.Surface molecularly imprinted polymers(SMIPs) were synthesized by surface grafting copolymerization method on the functionalized silica gel modified with β-cyclodextrin and vinyl group to selectively determine EGCG in aqueous media. The morphology and component of SMIPs were investigated by scanning electron micrograph, Fourier transform-infrared spectroscopy and thermogravimetric analysis, respectively. Molecular binding capacity, recognition property and selectivity of imprinted polymers were evaluated and the experimental results demonstrated that SMIP1 which combining hydrophobic recognition properties of β-cyclodextrin with hydrogen-bonding interactions of methacrylic acid, reached high specific recognition and binding capacity(61.58 mg/g) to template EGCG in aqueous media. Scatchard analysis suggested that two kinds of affinity binding sites existed in SMIP1 including the high affinity sites and low affinity sites.The iron oxide magnetic nanoparticles were employed as the substrate materials, and SiO2 was used to encapsulate the magnetic nanoparticles. Then magnetic SiO2 were functionalized by β-CD and MPS which were chemically bonded on their surfaces, and the core-shell magnetic molecularly imprinted polymers(MMIPs) were fabricated using a layer-by-layer self-assembly process. The resulting MMIPs were characterized by scanning electron micrograph, X-ray diffraction, Fourier transform-infrared spectroscopy and thermogravimetric analysis, respectively. The average diameter of MMIPs was about 400-500 nm, and the imprinting shell took 24.8% of the whole nanoparticles. With the help of an external permanent magnet, MMIPs can be completely isolated from the matrix in dozens of seconds. Moreover, MMIPs exhibited a fast adsorption kenitics whthin 40 min to get adsorption equilibrium, and the second-order kinetic model fitted the adsorption dynamic experimental datas well indicating that the chemisorption might be the rate-limiting step. Finally, compared with GCG and C, MMIPs showed a high specific recognition to template EGCG with the selective coefficients were 1.776 and 3.398, respectively.The SMIPs and SNIPs were employed as adsorbents of solid-phase extraction to make MISPE column and NISPE column. After optimization of the MISPE process, the MISPE column was utilized to purify tea polyphenols samples and a high purity of EGCG was obtained. Besides, it was utilized to enrich trace level of EGCG in the toothpaste samples coupled with HPLC, which provided a new way to determinate EGCG in real samples. The repeatability and accuracy of the proposed method were collected by the toothpaste samples spiked with EGCG at three different levels. HPLC analysis showed a linear dynamic range of 0.2-50 μg/mL with the correlation coefficient 0.9998 and the recoveries ranged from 89.4% to 97.0%. The limit of detection and quantification were 0.17 μg/m L and 0.33 μg/mL, respectively. In addition, the conditions of magnetic solid-phase extraction were optimized to obtain a suitable adsorbent dosage of 10 mg and the elution time of 20 min. |
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