Preparation of Porous Magnetic Molecularly Imprinted Polymer Microspheres for Accurately Recognizing ¦Á-Naphthylacetic

KeyWord:magnetic molecularly imprinted polymers  ¦Á-naphthylacetic  soap-free liquid emulsification method  tomato juice

Abstract:

      Molecular imprinted polymers£¨MIPs£© play a important role in the separation and enrichment of trace substances due to their specific recognition capability£®In this paper£¬a method for preparing porous magnetic MIPs£¨mMIPs£© microspheres was developed via the oil-in-water soap-free liquid emulsification technique to cope with a widely used pesticide ¦Á-naphthylacetic£¨NAA£©£®The preparation was done by simply mixing methacrylic acid£­styrene polymer precursor£¬NAA£¬Fe3O4 magnetic fluid and 2£¬2-azobisisobutyronitrile together in one pot£®The product was characterized by scanning electron microscopy£¬transmission electron microscopy and Fourier transform infrared spectroscopy£¬respectively£®The results showed that it is a kind of microspheres with a size distribution about 80 ¦Ìm£®And there are lots of pores distributed in/on the particle with diameters ranging from 1 to 10 ¦Ìm£®Such a porous structure could effectively increase the specific surface area£¬the number of contact recognition sites and the column capacity of the MIPs£¬as well as the mass transfer rate£®Adsorption kinetics experiments showed that the adsorption equilibrium could be reached in 120 minutes£®Meanwhile£¬the results of the adsorption isotherms and Scatchard analysis revealed that there exist two type of affinity binding sites for NAA in the MIPs£®The dissociation constant and apparent maximum binding capacity were found to be £­128.20 ¦Ìg¡¤mL£­1 and £­19.50 mg¡¤g£­1 for the low affinity binding site£¬and 161.30 ¦Ìg¡¤mL£­1 and 29.35 mg¡¤g£­1 for the high affinity binding site£®As comparison£¬there only existed one type affinity binding site for none-imprinted MIPs with the dissociation constant and apparent maximum binding capacity of 61.39 ¦Ìg¡¤mL£­1 and 4.658 mg¡¤g£­1£¬respectively£®Moreover£¬the results of the adsorption kinetics studies confirmed that the adsorption process matched the pseudo-second-order kinetic model well£¬indicating that it was controlled mainly by chemical adsorption£®All results demonstrated the high specificity of mMIPs towards NAA£®To investigate the feasibility of the mMIPs£¬they were used in the determination of NAA in real sample of tomato juice by high performance liquid chromatography with UV£­Vis detector£®The average recoveries for the sample at three spiked levels ranged from 78.7% to 89.2%£¬with relative standard deviations£¨RSDs£© less than 3.9%£¨n = 3£©£®Notably£¬the average recoveries still could reach 80.3% even when the amount of NAA in tomato juice is only 0.005 ¦Ìg¡¤mL£­1 which is far lower than the maximum residue limits of NAA stipulated by GB and the European Union£¨100 and 60 ¦Ìg¡¤kg£­1£¬respectively£©£®All experimental results indicated that it was readily to perform the preparation with the proposed method£¬and the mMIPs exhibited many merits£¬including the high selectivity and specificity for NAA£¬the fast mass transfer rate and the easy operation£®With the MIPs£¬the high matrix effects of real samples could be eliminated effectively£¬and the accuracy and reliability could be improved significantly for NAA determination in practice.