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Abstract: Tyrosine and phenylalanine imprinted Fe3O4/P(St-DVB) composite beads with magnetic susceptibility were prepared by suspension polymerization using Fe3O4 as the magnetically susceptible component, methacrylic acid and acrylamide as functional monomers, styrene and divinylbenzene as polymeric matrix components, stearic acid as porogen, and poly(ethylene glycol) 4000 as dispersant. Scanning electron microscopy examination of the composite beads showed macropores on the surface of spherical beads. The diameters of the composite beads and the macropores were in the ranges similar to 400-450 and 4-20 mum, respectively. The average content of Fe,04 inside the composite beads was 3.78%, and Fe3O4 was unevenly distributed. The mechanism of macropore formation and the concept of "intellectual cavity" of molecularly imprinted composite beads were proposed. The recognition selectivity of the composite beads was investigated using tyrosine and phenylalanine as both templates and comparative molecules. Tyrosine-imprinted composite beads exhibited a good recognition selectivity for tyrosine, and the separation factor was up to 3.67. In contrast, phenylalanine-imprinted composite beads had little recognition selectivity for phenylalanine and the separation factor was only 1.12. It was confirmed that the three-site interaction between tyrosine and functional monomers was stronger than the two-site interaction between phenylalanine and functional monomers. (C) 2003 Wiley Periodicals, Inc