Preparation, Characterization And Application Of Clopyralid Molecularly Imprinted Microspheres

Molecularly imprinted polymers(MIPs) are synthetic polymers with specific cavities designed for template molecules. It has a better selectivity as a pre-treatment sorbent. The application of MIPs has raised widespread attention. Clopyralid(3,6-dichloropyridine-2-carboxylic acid or 3,6-DCP) is an herbicide of synthesized hormones for controlling asteraceae, leguminosae, solanaceae and umbelliferae weeds in rape, maize and lawn. Because of the extensive use of 3,6-DCP, they cause a certain degree of pollution on the soil and water. A novel and fast determination method appropriate for pesticide residues is necessary.The objective of this paper is to prepare clopyralid MIMs and hydrophilic MIMs and apply for the dispersive solid-phase extraction(DSPE) technique. This paper includes the following contents:First, the MIMs for 3,6-DCP were successfully synthesized via precipitation polymerization using methacrylic acid(MAA) as a functional monomer, ethylene glycol dimethacrylate(EGDMA) as a cross-linker and mixture of butanone(MEK) and N-heptane(6:4,v:v) as a porogen. The best ratio of template: MAA: EGDMA was 0.7:4.2:21.Second, the morphologies, particle sizes, structures of polymers were investigated systematically. The microspheres with monodispersity had regular shape and clear surface. The average particle sizes of MIMs and non-imprinted microspheres(NIMs) were 2.76 μm and 2.15 μm.Third,the equilibrium adsorption experiments and Scatchard analysis showed that Qmax of MIMs and NIMs were 63.23 mg·g-1 and 58.17 mg·g-1. In the MIMs, there was specific recognition of the binding sites with uniform distribution. Langmuir isotherm displayed that adsorption of MIMs was attributed to monolayer-adsorption. In the binding kinetics analysis, the adsorption tended to reach saturation within 30 min. Lagergran pseudo-second order model demonstrated that adsorption type of MIMs towards 3,6-DCP was ascertained to chemical adsorption. Selectivity analysis revealed that MIMs possessed highly specific recognition for 3,6-DCP.Four, MIMs was used for extracting 3,6-DCP from soil spiked samples as the DSPE sorbent. This result showed that the average spiked recoveries were between 75% and 110%. The results meet the requirement of pesticide residue analysis.Fifth, the hydrophilic MIMs(GMA-MIMs) of 3,6-DCP were successfully synthesized used by GMA as the hydrophilic co-monomer. The best ratio of MAA:GMA:EGDMA was 4.2:4.2:21.Sixth, the hydrophilic MIMs were characterized by scanning electron microscopy, particle testing, FT-IR analysis. The polymers with monodisperse distribution had satisfied morphology after using GMA. The average particle size of hydrophilic MIMs was 2.82μm.Seventh, adsorption capacity of GMA-MIMs was higher than MIMs in distilled water. The data of quilibrium adsorption experiments was extremely fitted Freundlich adsorption isotherm model that showed adsorption type was chemical adsorption.Eighth, the hydrophilic imprinted microspheres performed high purification efficiency and satisfied recoveries in water spiked with 3,6-DCP. This proposed approach successfully provided science basis for residue determination of 3,6-DCP in water phase. So that molecular imprinting technique will have a good prospect in future applications.