Specific enrichment of caffeic acid from Taraxacum mon-golicum Hand.-Mazz. by pH and magnetic dual-responsive molecularly imprinted polymers.

Specific recognition of caffeic acid (CA) from Taraxacum mon-golicum Hand.-Mazz. was successfully performed using a new pH responsive magnetic molecularly imprinted polymers (pH-MMIPs) by simple surface molecular imprinting polymerization. The pH-MMIPs were prepared on the surface of the Fe3O4@SiO2@MPS particles using CA as a template, 2-(dimethylamino) ethyl methacrylate (DMA) as the pH responsive functional monomer, 4-vinylpyridine (4-VP) as an assisting functional monomer, ethylene glycol dimethyl acrylate (EGDMA) as cross-linker, 2,2'-azobisisobutyronitrile (AIBN) as initiator and methanol-H2O (1:1, v/v) as the porogen. The resultant polymers were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), vibrating sample magnetometry (VSM) and x-ray diffraction (XRD). The adsorption experiments revealed that the pH-MMIPs performed high adsorption ability (11.5 mg g-1) by changing solution pH. Successful selective adsorption of CA was achieved with distribution coefficient of 0.12 and 0.21 towards ferulic acid and chlorogenic acid. Furthermore, pH-MMIPs were employed as adsorbents for extraction and enrichment of CA from Taraxacum mon-golicum Hand.-Mazz. extract. The recoveries of CA in the Taraxacum mon-golicum Hand.-Mazz. ranged from 90.47% to 98.97%. The results proved that the polymers have the potential to provide a selective recognition of CA in complex samples by simple pH regulation.