Molecularly Imprinting Solid-phase Extraction Materials: Preparation And Its Application

Molecularly imprinted polymers are specific high polymer materials that have the selective binding ability to the particular molecules. Molecularly imprinted polymers have many advantages of good affinity, high selectivity, powerful anti-interference performance, better stability, as well as long life and wide range of applications. Molecular imprinting technology had been widespread used in more fields such as environmental monitoring, natural products separation and chromatographic analysis. But the preparations MIPs by using traditional bulk polymerization have many disadvantages, such as small binding capacities to templates, bad accessibility, difficult to completely eluting templates from MIPs, and as well as resulting in the determination accuracy. So it appears some new molecular imprinting technologies to solve the problems in these years, for example, surface imprinting technique, suspension polymerization, analog-imprinted polymer, and so on. As following were primary research results to be acquired in this paper:1. Molecular imprinted polymers (MIPs) were prepared through thermal polymerization by using quercetin as the template molecule, acrylamide (AA) as the functional monomer and ethylene glycol dimethacrylate (EDMA) as the cross-linker in the porogen of tetrahydrofuran (THF). The synthesized MIPs were identified by both Fourier transform infrared (FTIR) and scanning electron microscope (SEM), and it was showed that the complex ratio between AA and quercetin was 1:4 studied by UV spectrum. Systematic investigations of the influences of key synthetic conditions, including functional monomers, porogens and cross-linkers, on the recognition properties of the MIPs, such as THF and EDMA were conducted by using Computational quantum chemical analysis. Scatchard and Langmuir-Freundlich analysis revealed that the homogeneous binding sites were formed in the polymers. Besides quercetin, two structurally similar compounds of rutin and catechol were employed for molecular recognition specificity tests of MIPs. Binding study demonstrated that MIPs showed excellent affinity and high selectivity to quercetin. Accordingly, the MIPs were used as a solid-phase extraction (SPE) sorbent for the extraction and enrichment of quercetin in cacumen platycladi samples, followed by HPLC-UV analysis. The application of MIPs with high affinity and excellent stereo-selectivity toward quercetin in SPE might offer a novel method for the enrichment and determination of flavonoid compounds in the natural products.2. A novel molecularly imprinted sol-gel material was synthesized by combining a surface molecular imprinting technique with a sol-gel process on the supporter of amino-functionalized silica gel for solid-phase extraction-high performance liquid chromatography (SPE-HPLC) determination of 2.4-dimethylphenol (DMP). Non-imprinted silica sorbent was synthesized without the addition of 2,4-dimethylphenol using the same procedure as that of MIPs. The 2,4-DMP-MIP and NIP were characterized by FT-IR and the static adsorption experiments. It was showed that the prepared DMP-imprinted silica sorbent had good performances of high adsorption capacity and good site accessibility for 2,4-DMP. The maximum static adsorption capacity of the MIP and NIP for DMP was 374 and 171μg.g-1, respectively. The relatively selective factor value of this DMP-MIP was 2.2, and the 2,4-DMP-MIP was used as the sorbent in solid-phase extraction to determine 2,4-DMP in seawater samples with satisfactory recovery higher than 82.4%(RSD 5.1%). It was obvious that the MIP-SPE-HPLC method showed a higher selectivity to DMP, because the molecularly imprinted sol-gel materials by surface molecular imprinting technique could reduce the embedding phenomenon of MIP to templates, and resulting in speeding up mass transfer and benefitting templates eluting or rebinding in MIPs.3. Double molecularly imprinted polymeric microspheres (DMIPMs) was prepared via heat-initiating polymerization with naphthalene and anthracene as the template molecule, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross linker and polyvinyl alcohcol as dispersant by using suspension polymerization. Dispersive solid-phase microextraction method was proposed to study the molecular recognition of 2-3 cycles PAHs pollutants in seawater with the DMIPMs. The effects of mixing speeds to spherulization were characterized by means of SEM. The reason of double template molecule molecular imprinting effect occurred was studied by ultraviolet spectra method. It was studied of the two selective sites in DMIPMs by static adsorption experiments and Scatchard analysis. Experimental results show that the prepared DMIMP exhibits high selectivity and good recognition ability to naphthalene and anthracene than that of the MIPMs using single template molecule. The possible reasons were that the mutual effect model of double template molecule optimizing the cavities of molecularly imprinted polymer (MIP) and increasing the multi-resistance of MIP. The recognition ability of prepared DMIPM didn't show descend even if the DMIPM was used repeatedly for 3 times. The preparation of the DMIPM provides an innovative opportunity for the development of the novel material for selective enrichment and determination of trace 2-3 cycles PAHs in complex seawater.4. A novel surface imprinting material was synthesized using a template immobilized on a modified silica gel matrix where naphthyl acetic acid was grafted to aminopropyl silica. The silica template conjugate was co-polymerized with a functional monomer (methacrylic acid) and cross-linker (ethylene glycol dimethacrylate), and then the silica-polymer composites were treated with an aqueous NH4HF2 solution to dissolve the silica matrix. FT-IR spectrum and scanning electron microscope (SEM) were adopted for characterization the surface and structure of the molecularly imprinted polymer. The binding energy of imprinted molecule with functional monomer was calculated by using the density functional theory (DFT) method, and the largest binding energy could be chosen for the synthesis of molecularly imprinted polymer (MIP). Competitive rebinding test was carried out in seawater media, and the selective adsorptions of target molecule on MIP were studied. The resulting polymer was found as specific affinity toward naphthalene and phenanthrene. The reason for the higher sensitivity to phenanthrene owe to the size of the carboxyl group, where the imprint molecule was larger than naphthalene. So it was possible to preconcentrate the structural analogues of naphthalene for seawater by using the analog-imprinted polymer in the future.5. The coupling of ultrasound-assisted dispersive liquid-liquid microextraction with little solvent consumption (USA-DLLME-LSC) for gas chromatography-mass spectrometry (GC-MS) determination of 16 typical kinds of polycyclic aromatic hydrocarbons (PAHs) in seawater samples was studied. Some important factors that potentially affecting the microextraction processes and the enrichment efficiency were systematically investigated, such as extraction solvent, dispersive solvent, phase ratio, extraction temperature and time, sodium chloride concentration, and content of humic acid. A 6 mL seawater sample was placed in a 10 mL glass-centrifuge tube. Then 0.05mL 6.15 mol. L-1 NaCl and 80μL mixed organic solvents (TCE:DE=3:7, V/V) were added into the tube. The resulting mixture was immersed into an ultrasonic bath for 5 min at 35℃. The resulting emulsion solution was centrifuged at 8000 rpm for 5 min and then 1μL aliquot of the TCE phase was removed from the conic bottom of the centrifuge tube and injected into GC-MS system for analysis. Under the optimized conditions, enrichment factors (EFs) ranging from 722 to 8133 were obtained, and allowing achieving limits of detection at 0.05-10.0ng.L-1.The proposed USA-DLLME method attained about 1.1-10 times higher EFs than those in the traditional DLLME method. The recoveries of PAHs from simulated seawater samples were 65-145%, that for real seawater was 67-122%, correspondingly. So the USA-DLLME coupled to GC-MS was successfully applied to determinate PAHs in the environmental seawater samples.