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Study on Preparation of Triazine Herbicides Molecularly Imprinted Polymers and Application in the Trace Analysis and Detection

Author: ChenJun
Tutor: BaiLianYang
School: Hunan Agricultural University
Course: Pesticides
Keywords: Triazine Herbicides Molecularly imprinted Polymers Trace Analysis andDetection Solid phase (micro) exraction Chromatographic packings Magnetic composite microspheres Electrochemical sensor Stir-bar sorptiveextraction
CLC: S482.4
Type: PhD thesis
Year: 2013
Downloads: 23
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Abstract

Molecularly imprinted Polymers (MIPs) are a new kind of macromolecular materials with molecular recognition capability. Because MIPs have the advantages of predetermination, specificity and practicability, they have been extensively used in chromatographic separation, antibody mimic, solid-phase extraction, biosensors, catalyzing reaction and other relevant fields. The combination of conventional extraction technology, chromatographic separation and sensor technology with molecular imprinting technique, have been applied for the enrichment and separation of trace analytes in the complex environmental samples. This could solve some problems such as the complexity of environment samples and cumbersome process of the pretreatment and provide great convenience for the collection, enrichment and analysis. In this work we made a systematic study and carried out some improvement and innovation focusing on the solid phase (micro) extraction material, magnetic composite microspheres and electrochemical sensor by molecular imprinting technique, chromatographic column packing and stir bar sorptive extraction combined with the molecular imprinting technique. Furthermore, these developed materials were applied for the enrichment and separation of trace and trace sample processing using triazine herbicides as representative pesticide residues. The following studies are done in this paper.1. Atrazine imprinted polymers were comparatively synthesized using identical polymer formulation by far-infrared (FIR) thermal and ultraviolet (UV) light-induced polymerization, respectively. By ultraviolet spectrophotometry, equilibrium binding experiments were carried out at room temperature with the prepared MIPs. The results showed that MIPuv resulted in three-fold reduction in polymerization time and higher specific binding to atrazine compared with their MIPFIR counterparts. Scatchard plot’s of both MIPs indicated that the affinities of the binding sites in MIPs are heterogeneous and can be approximated by two dissociation-constants corresponding to the high-and low-affinity binding sites, respectively. Moreover, several common pesticides including atrazine, cyromazine, metamitron, simazine, ametryn, terbutryn were tested to determine their specificity, and similar imprinting factor and different selectivity index were obtained for both resulted MIPs. Physical characterization of the polymers revealed that the different polymerization methods led to the slight differences in both polymer structures and performance by scanning electron microscope (SEM), Fourier transform infrared absorption (FTIR), and mercury analyzer (MA). Finally, both MIPs were used as selective sorbents for solid phase extraction (SPE) of atrazine from lake water, followed by the determination using high performance liquid chromatography (HPLC). Compared with the commercial C18SPE sorbent (86.4%-91.5%), higher recoveries of atrazine in spiked lake water were obtained in the range of93.1%-93.8%and94.3%-94.5%, for both MIPs, respectively.2. Atrazine molecularly imprinted polymer microspheres (MIPMs) were fabricated by two step seed swelling polymerization method, using atrazine as a template molecule, methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EDMA) as a crosslinking agent and toluene/dodecanol as a porogenic agent, and the factors influencing on the shape, the particle size and particle size distribution of the MIPMs were detailedly studied such as swelling ratio, stirring rate, water-oil ratio, and dispersant dosage, etc. The results showed that when the swelling ratio was40, the stirring rate was200rpm, the water-oil ratio was3:1(v/v), the functional monomer MAA was6mmol, the EDMA dosage was30mmol and the PVA dosage was0.6g, a series of MIPMs with even particle size of3-5μm and good dispersivity could be obtained. We adopted an equilibrium binding experiment to study the binding capacity of the polymer with template molecule, and found through Scatchard model analysis that, for the imprinted polymers, the dissociation constant and apparent maximum binding capacity of low affinity binding site were Kd1=8.21x10-3mol/L and Qmax1=334.23μmol/g, respectively, and those of high affinity binding site were Kd2=4.36x10-4mol/L and Qmax2=38.07μmol/g, respectively. We packed the polymers into empty chromatographic steel tube columns (2.1mm I.D.x10cm) to prepare liquid chromatographic columns used for the evaluation of specificity with similar structure compounds and the determination of atrazine content in water samples. The proposed method has been successfully applied to the determination of limited atrazine in water samples. The results showed that a good linear relationship of atrazine was maintained within0.01-10mg/L (r=0.9992), the sample recovery was in a range of92.1%-102.0%, with a RSD lower than5%(n=6) and a detection limit of4.13μg/L.3. Magnetic iron oxide submicron particles were prepared by chemical co-precipitation, and then magnetic Fe3O4@SiO2@γ-MAPs composite microspheres were achieved by sol-gel technology. The magnetic molecularly imprinted beads were prepared utilizing atrazine as the template molecule by suspension polymerization. The structural characteristics and extraction performance of the atrazine magnetic molecularly imprinted beads were investigated. The imprinted beads were characterized by scanning electron microscopy, fourier transform infrared spectroscopy, vibrating sample magnetometer(VSM) and energy-dispersive X-ray spectroscopy (EDX). The results showed that the imprinted beads were in spherical shape with diameter1.2μm and the surface Was porous and rough. We adopted an equilibrium binding experiment to study the binding capacity of the MMIPs with template molecule, and found through Scatchard model analysis that, for the MMIPs, the dissociation constant and apparent maximum binding capacity of low affinity binding site were Kd1=6.306×10-4mol/L and Qmax1=22.12μmol/g, respectively, and those of high affinity binding site were Kd2=2.887×10-3mol/L and Qmax2=65.94μmol/g, respectively. The atrazine magnetic molecularly imprinted beads were coupled with HPLC for the analysis of three triazines (atrazine、ametryn、 terbuthylazine). The proposed method presented good linearity and the detection limits was2.6μg/L～5.2μg/L. This method was used to the simultaneous quantification of three triazines in soil samples. The recoveries were from80.7%to116.6%for the spiked soil respectively, with the RSD of2.11%～6.92%.4. A novel sensor for the determination of terbuthylazine (TBA) based on3-thiophenemalonic acid (3-TMA) as functional monomer was fabricated by molecularly imprinted technology. The polymeric film was obtained on the gold electrode surface by electrocopolymerization of3-TMA in the presence of the template molecule of TBA, through the use of cyclic voltammetry (CV). Several important parameters controlling the performance of the molecularly imprinted polymer modified sensor were investigated in detail such as the monomer concentration, the electropolymerization cycles and pH. The obtained MIP sensor is highly specific towards newly added TBA and the recognition can be quantitatively analyzed by the differential pulse voltammetry (DPV) to verify the changes in oxidation currents of ferricyanide. In the optimal condition, the response of the imprinted sensor to TBA was linearly proportional to its concentration over the range2.5×10-7mol/L to1.2×10-4mol/L, with high selectivity, good stability and reproducibility (RSD,2.05%). The method has been successfully applied to the determination of TBA in real samples, with a recovery ranging from71.2%to84.9%and a detection limit of2.0×10-8mol/L (S/N=3).5. A novel method to fast prepare molecularly imprinted polymer monolithic fibers is developed with the help of microwave irradiation and used to overcome the well known water-compatibility problem of MIP by liquid-liquid-solid microextraction (LLSME) and the developed hollow fiber-liquid-solid microextraction (HFLSME) system. The resulted atrazine MIP fiber was obtained after silica being etched away with a controlled length of1cm, and subsequently characterized by scanning electron microscope. Main factors affecting the selective extraction including extraction time, desorption time, extraction and desorption solvents were investigated for LLSME and HFLSME procedures in detail. The selectivity was also evaluated using the atrazine template molecule and its structurally-related compounds including2-amino-4-methoxy-6-methyl-1,3,5-triazine, terbuthylazine, ametryn and metribuzin pesticides. The extraction ratio for target pesticides was increased to more than10times in atrazine-imprinted polymeric monolithic fiber compared to non-imprinted polymeric monolithic fiber. The resulted fibers were successfully applied to detect atrazine and its analogues pesticides in lake water coupled to HPLC and resulted in recoveries in the range of68.3%to113.2%, respectively. It demonstrated that the proposed technique could overcome the problem of disturbance from water when the MIP monolithic fiber was exposed directly to non-polar solvent above the aqueous solution.6. To overcome the shortcomings of commercial Stir-bar sorptive extraction, a novel stir bar for sorption extaction based on monolithic material was prepared. The new matrix high magnetic and super paramagnetic material Nd2Fe14B magnetic powder as a muddler magnetic supply, then magnetic powder by TEOS cladding y-MAPs by surface grafting were achieved by sol-gel technology. The molecularly imprinted stir bar sorptive extraction were prepared utilizing atrazine as the template molecule, MAA as the functional monomer, EDMA as the crosslinker, chloroform as the porogen, by in-situ stepwise polymerization. It was then used to extract compound triazine herbicides in the environmental soil and cucumber sample. A method was established by optimizing the experimental conditions such as adsorption curve, stir rate, extraction time, desorption mode and desorption solvent. The method had a good linear relationship in the concentration range of0.01-0.3μg/mL with a correlation coefficient of0.9993. The recovery was from73.6%to95.5%. The SBSE was successfully used to extract triazine herbicides.

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CLC: > Agricultural Sciences > Plant Protection > Pesticide ( chemical control ) > Various pesticides > Herbicides ( herbicide )
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