Preparation Of Hydrophilic Adsorption Resins And Their Applications In The Determination Of Triazine Herbicides In Food And Environmental Samples

To accurately quantify target pollutants in complex environmental and food samples,various new adsorbents have been widely developed for the selective enrichment of the target pollutants.Molecularly imprinted solid-phase extraction?SPE?has been widely used in the selective enrichment of target pollutants in the complex real samples due to the advantages of selective recognition of the imprinted materials,and simple operation and solvent-saving in solid phase extraction?SPE?.However,the preparation of hydrophilic imprinted materials which maintain excellent selectivity in water environments has always been a challenge.Therefore,the development of hydrophilic imprinting materials that can maintain the selective recognition ability in aqueous media has become a hot and difficult point in the development of imprinted materials.In this paper,the residual triazine herbicides in food and environmental samples were acted as the target analytes.Four new types of hydrophilic adsorption resins?three of which are hydrophilic imprinted resins?were prepared by using the cheap and readily available hydrophilic raw materials?melamine,formaldehyde and resorcinol?.The preparation processes were based on the preparation technology of the traditional resin materials and without the aid of allylic monomers and nitrogen gas.The four adsorption resins were used as an SPE adsorbent combined with high performance liquid chromatography and tandem mass spectrometry to detect triazine herbicides in aqueous media samples and satisfactory results were achieved.This paper mainly contains the following five parts.In chapter one,the triazine herbicides were introduced.The research background of solid phase extraction and molecular imprinting technology was summarized.The research progress of water-compatible or hydrophilic imprinting materials was emphasized.In chapter two,monodisperse super-hydrophilic melamine-formaldehyde-resorcinol resin?MFR?microspheres were prepared by microwave-assisted condensation,and the preparation processes without the participation of surfactants or stabilizers.By investigating the yield and morphology of the MFR,the microwave preparation conditions were optimized and the possible causes were analyzed.The obtained monodisperse MFR microspheres have a narrow particle size distribution and the particle size of about 2.5?m.Under optimized extraction and HPLC-MS/MS conditions,the MFR was used as SPE sorbent to extract six triazines in three fruit juice samples.The established MFR-SPE-HPLC-MS/MS method exhibited excellent linearity?R²>0.9994?and precisions?RSD<8%?,and the recoveries were in the range of 90-99%.In chapter three,monodisperse hydrophilic molecularly imprinted resin?MIRs?microspheres were prepared in water by using resorcinol and melamine as hydrophilic monomers,formaldehyde as a hydrophilic cross-linking agent,acetonitrile as a porogen,and ametryn as template.The one-step preparation process did not require the assistance of nitrogen and allyl-based hydrophilic functional monomer,and the condensation processes without stirring.The obtained MIRs microspheres exhibited good monodispersity and excellent hydrophilicity.The experiments of isothermal adsorption and selective adsorption show that the obtained MIRs microspheres have higher selectivity for the ametryn and its analogues.Under the optimized experimental conditions,the MIRs were directly used for the analysis of triazines in five water-diluted honey samples.The established MIRs-SPE-HPLC-MS/MS showed a lower detection limits(0.02-0.15 ng g^-1)and matrix effects?-1.0-10.8%?,satisfactory precisions?3-8%?and recoveries?83-97%?.In chapter four,firstly,Fe₃O₄@NH₂ were prepared by a one-step solvothermal method.Then,the magnetic superhydrophilic molecularly imprinted resin?MMIRs?microspheres were prepared by using melamine and resorcinol as hydrophilic functional monomers,formaldehyde as hydrophilic crosslinker,acetonitrile as porogen,and ametryn as template.The obtained MMIRs microspheres have a high yield?77.7%?,superhydrophilicity?completely immersed by water in 3 s?,excellent magnetic separation ability?collected by an external magnetic field within 10 s?.Isothermal adsorption and selective adsorption experiments showed that the prepared MMIRs have excellent selectivity for triazines.Under optimized experimental conditions,the MMIRs can be directly used for the selective extraction of triazines in aqueous media samples.The established MMIRs-SPE-HPLC-MS/MS method showed a lower detection limits(0.02-0.07?g L^-1)and higher recoveries?85-101%?.In chapter five,magnetic super-hydrophilic imprinted composite resins?MWNTs@Fe₃O₄@MIR?were prepared by the condensation of melamine,resorcinol and formaldehyde on the surface of magnetic multi-walled carbon nanotubes?MWNTs@Fe₃O₄?.The influence of the template?ametryn?on the surface imprinting efficiency of the MWNTs@Fe₃O₄@MIR was investigated.The obtained MWNTs@Fe₃O₄@MIR had superhydrophilicity and excellent magnetic separation ability.The isothermal adsorption,selective adsorption and adsorption kinetics experiments show that the MWNTs@Fe₃O₄@MIR exhibit good specific recognition ability for triazines.The adsorption isotherm obeyed to the Freundlich isothermal model,and the adsorption kinetics conformed to the pseudo second-order kinetic model.Under the optimized conditions,the MWNTs@Fe₃O₄@MIR was successfully used as selective sorbent to directly enrich and detect six triazines in five environmental water samples combined with HPLC-MS/MS.The established MWNTs@Fe₃O₄@MIR-SPE-HPLC-MS/MS method showed lower detection limits(0.007-0.068?g L^-1)and higher precisions?RSD<9%?,and the recoveries were in the range of 88-100%.