Study On Preparation Of Two Novel Magnetic Nanocomposites And Their Applications In The Environmental Medicine

Since the World War Ⅱ, with the rapid development of the global economy, people’ living quality has been improved. However, over the past several decades, a wide range of chemical contaminants have been released to the aquatic environment by discharge of untreated industrial, agricultural and urban wastewaters, which made the aquatic ecosystems damaged severely. Especially, some organic pollutants have great harmful effect on public health due to their properties of high toxicity, bioaccumulation and persistence. These chemicals can accumulate in human tissues and organs, and cause short-term or long-term harms for human health.The development of industrialization of agriculture made the agricultural production dependent on the use of pesticides, antibiotics and hormones. Unfortunately, the unreasonable use of these chemicals can result in the residue in agricultural products, which is the major source for human inadvertent intake, and some diseases, such as acute toxicity, allergic reaction, endocrine disorde, and even cancer may occur to human.Therefore, supervising the pollutants in environment and the residual chemicals in foodstuffs, and then systematically and objectively reflecting the dynamic changes of pollutants and the concentrations of residual chemicals, are highly necessary to develop the assessment system of human exposure and corresponding health hazards, and then put forward the relevant regulations and laws. Most importantly, the sample pretreatment is the key point of accurate quantification of trace analytes in samples. In this study, perfluorinated compounds (PFCs) in surface water and macrolide antibitics (MACs) in foodstuffs that are closly related to human life are chosen as research subjects. The study on the preparation of two novel magnetic nanocomposites with selective recognition abilities and their applications in enviromental pollution monitoring and food safety were gradually carried out.The whole study is composed of the following five parts:Chapter Ⅰ:Study on preparation of a novel magnetic nanocomposite for selective recognition of perfluorinated compounds and adsorption performance evaluationF-F interaction often occurs between a fluorous portion of a molecule and highly fluorinated solvent or solid phase. In recent years, a fluorous separation technique based on F-F interaction has been used for purification and isolation of target analytes. In this study, a novel magnetic nanocomposite for selective recognition of PFCs was prepared by using fluorous and amino monomers. In the first place, highly water-dispersible Fe3O4nanoparticles (NPs) capped with carboxyl (Fe3O4-COOH NPs) were synthesized by a modified interfacial coprecipitation method. Fe3O4-COOH NPs have a nearly spherical shape and narrow size distribution with a average diameter of10nm. The hydrophilic particles are able to be kept stable for more than2weeks in water. The magnetic nanocomposite (Fe3O4@SiO2-NH2&F13) functionalized with amino group and octyl-perfluorinated chain was prepared in one step based on sol-gel technology using Fe3O4-COOH NPs as substrate. Fe3O4@SiO2-NH2&F13has a core-shell structure with silica shell thickness of about2nm. In Fourier transform-infrared (FT-IR) spectra, the occurrence of absorption peaks at1560,1194and1145cm-1confirmed the existence of-NH2and C-F bond on the surface of the nanocomposite. The saturation magnetization (Ms) of the nanocomposite is40.5emu g-1, which makes it be isolated rapidly by an external magnetic field. Furthermore, good water-compatibility of the nanocomposite can effectively inhibit the matrix components from binding on its surface base on hydrophobic interaction in complex aquatic enviroment. Thereafter,1H,1H,2H,2H-perfluoro-1-octanol (6:2FTOH), n-octanoic acid (n-OA),2-fluorophenylacetic acid (2-FPAA),3,4-dihydroxyphenylacetic acid (3,4-DHPAA), florfenicol (FTAP) and erythromycin (ERY) were used as reference compounds, and the selectivity of Fe3O4@SiO2-NH2&F13for PFCs was evaluated. The results demonstrated that the magnetic nanocomposite had favorable selectivity for PFCs due to electrostatic and fluorous interaction as well as size exclusion effect. The sorption isotherms of Fe3O4@SiO2-NH2&F13for PFCs were fitted by Langmuir and Freunlich model. The results revealed that the adsorbed PFCs formed monolayer coverage on the nanocomposite surface in ethanol and the adsorption capacities for PFCs were in the range of12.97-129.51mg g-1. On the other hand, in aqueous solution, due to the hydrophobicity of perfluoroalkyl chain, PFC molecule containing eight or more carbon atoms may stick together with each other on the nanocomposite surface to form bilayer, hemi-micelles and micelles, which made the adsorption capacities of Fe3O4@SiO2-NH2&F13for these PFCs were greatly enhanced, even higher than1000mg g-1for PFCs with long C-F chain (C>9). Therefore, the magnetic nanocomposite has a wide prospect for PFC trace analysis and removal of PFCs from environmatal medium. Chapter II:Rapid determination and occurrence investigation of perfluorinated compounds in surface water from East Lake based on magnetic solid-phase extractionPFCs have been detected in virious aquatic environments, where most of PFCs are typically present at ng L-1levels. Development of a rapid and senstive determination technique is important to accurately reveal contaminative situation of PFCs in surface water. In this study, using the prepared Fe3O4@SiO2-NH2&F13as adsorbent, a convenient, rapid and effective magnetic solid-phase extraction (MSPE) procedure was established for enrichment and clean-up of9PFCs in surface water samples. An ultra high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) system was employed for the deection of PFCs after preconcentration with the magnetic nanocomposite. Under the optimal MSPE conditions, enrichment factor of1000was achieved by extracting PFCs from500mL of water sample and redissolving the analytes in0.5mL of solvent. The developed analytical method had a good linearity in the range of0.097-100ng L-1(R2>0.9917), and the limits of detection (LODs) ranged from0.029to0.099ng L-1. At three different fortified concentrations of0.5,5and50ng L-1, the spiked recoveries of PFCs ranging from90.05to106.67%were obtained with relative standard deviations (RSDs) in the range of3.11-12.62%. Compared with BS ISO25101:2009standard method using Oasis-WAX (mixed-mode weak anion exchanger) as SPE absorbent, the developed method based on MSPE using the magnetic nanocomposite as adsorbent exhibited a smoother chromatogram baseline, and the matrix interferences were effectively eliminated, as well as the response singals of PFCs greatly enhanced. Afterwards, three lakelets (Guozhen, Niuchao and Tangling) of East Lake were selected in this study, and8,6and3representative sampling sites along the lakeshore was located by Global positioning system (GPS), respectively.The proposed method was applied for determination of PFCs in surface water from East Lake. The total concentrations of9PFCs in water samples were in the range of30.12-125.35ng L"1, indicating the widespread contaminations of PFCs in the surface water of East Lake. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were the most prevalent PFCs. In addition, the greatest concentrations of PFCs were observed in Niuchao lakelet loaded with the most recreational activities. Though the concentrations of long-chain PFCs (Cl1, C12, C14) in most of water samples (>70%) were less than the limits of quantification (LOQs), these PFCs are potential to accumulate in sediment and aquatic biota, indicating that a comprehensive survey is necessary for future studies of characterizing PFCs and their distribution in East Lake. Chapter Ⅲ:Study on application of Fe3O4@SiO2-NH2&F13for selective removal of perfluorinated compounds from surface water sample of Yangtze RiverAt present, during the drinking water treatment, conventional techniques, including sandfiltraton, ozonation, chlorination and activated sludge purification, are difficult to remove PFCs. Though some advanced techniques, such as ultrasonic irradiation and reverse osmosis, can remove PFCs effectively, taking environmental protection and cost saving into consideration, adsorption is the most suitable technique for PFC removal from aquatic enviroment. In this study, the prepared Fe3O4@SiO2-NH2&F13was used as a selective removal material and the removal efficiency for PFCs was investigated systematically. In the first place, the effects of sorption time, temperature and pH value of aqueous solution on the adsorption performance of Fe3O4@SiO2-NH2&F13for PFCs were investigated respectively. The results showed the sorption equilibrium was achieved in5min, much less than the time required for anion exchange resin (e.g. IRA67) and powder activated carbon (PAC). The binding amounts of Fe3O4@SiO2-NH2&F13for PFCs decreased slightly with the increasing of temperature, revealing an exothermic nature of the sorption of PFCs onto the magnetic nanocomposite. The adsorption performance of Fe3O4@SiO2-NH2&F13for PFCs was influenced significantly when aqueous solution pH was above10, especially for short-chain PFCs (C<10). Thereafter, Fe3O4@SiO2-NH2&F13was used for the removal of PFCs from surface water samples of Yangtze River. The removal effeciency was compared with that of IRA67and PAC. In1L of spiked water sample fortified at0.5,5and50ng L"1levels, the magnetic nanocomposite had removal effeciency of86.29%for PFCs in0.5h. By contrast, only12.86%and58.61%of PFCs were removed by IRA67and PAC, respectively. Furthermore, the magnetic nanocomposite exhibited good removal performance for each PFC and the removal ratios for most of PFCs were above80%, except perfluorohexane sulfonic acid (PFHxS) and perfluoroheptanoic acid (PFHpA)(63.06-72.99%and64.71-75.53%, respectively). At the same time, humic acid (HA)(5-50mg L-1) was used to investigate the matrix interference for the removal efficiency of Fe3O4@SiO2-NH2&F13, and the results confirmed that the presence of HA had no significant influence on the removal performance for PFCs. At a HA concentration of50mg L1, the removal efficiency of the nanocomposite for PFCs only had9.81%reduced, but a reduction of41.48%occurred to PAC. Meanwhile, the magnetic nanocomposite could be reused for several times without obvous decrease in the removal efficiency. Therefore, the obtained results demonstrated Fe3O4@SiO2-NH2&F13could be used as an effective adsorbent for rapid and selective removal of PFCs from surface water. Chapter IV:Study on preparation of magnetic molecularly imprinted nanocomposite for selective recognition of macrolide antibitics and adsorption performance evaluationMolecularly imprinted polymers (MIPs) possess predetermined selectivity for template molecule and a group of structurally related compounds based on shape matching and functionality interaction between target analytes and imprinted cavities. The nanocomposite prepared by coating a system of selective recognition onto the surface of NPs combines selectivity and magnetic responsibility and has rapid sorption rate for target analytes. In this study, based on surface molecular imprinting technology, a novel magnetic nanocomposite (Fe3O4@SiO2@MIPs) was prepared by grafting molecularly imprinted polymers (MIPs) onto the surface of Fe3O4NPs with erythromycin as template molecule. Fe3O4@SiO2@MIPs has core-shell structure and the obvious C=O streching vibration peak in FT-IR spectra confirmed the existence of MIPs on surface of Fe3O4NPs. The magnetic nanocomposite has superparamagnetism with Ms of3.2emu g-1. Scatchard analysis was employed to estimate the binding properties of Fe3O4@SiO2@MIPs for ERY. The results revealed that heterogeneous binding sites existed on the surface of the nanocomposite and these sites exhibited different affinity for ERY. Fe3O4@SiO2@MIPs had high adsorption capacity of94.1mg g-1for ERY and the imprinting factor was11.9, which indicated good imprinted effect for ERY. Meanwhile, fluoroquinolone and amphenicol antibiotics were used as reference compounds and the selectivity of Fe3O4@SiO2@MIPs for MACs was evaluated. The results confirmed the magnetic nanocomposite showed favorable selectivity for multiple MACs. Thus, Fe3O4@SiO2@MIPs could be used as an effective and selective magnetic solid-phase extraction (MSPE) adsorbent for complex sample pretreatment. Chapter V:Study on applicaton of magnetic solid-phase extaction-high-performance liqid chromatography-ultraviolet detection method for rapid determination of macrolide antibiotics in foodstuff samplesMost of MACs (e.g. erythromycin, azithromycin) lack specfic chromophore. Normally, non-selective and low ultraviolet wavelength often be used when a high-performance liqid chromatography-ultraviolet detection (HPLC-UV) system was employed for the quantification of MACs. Thus, in order to realize selective and sensitive determination of MACs, an effective sample treatment is highly required to eliminate matrix interferences. In this study, a rapid and convenient magnetic solid-phase extraction (MSPE) procedure was established using Fe3O4@SiO2@MIPs as adsorbent for selective exraction6MACs in foodstuff samples. A mass of100mg magnetic nanocomposite was immersed in20mL of sample extractant and MACs were selectively adsorbed on the nanocomposite. After5min, the nanocomposite was separated by an external magnetic field and non-selectively adsorbed matrix components were removed by10mL of acetonitrile:H2O (2:8, v/v). Finally, MACs adsorbed on the nanocomposite were eluted by10mL methanol:50mM KH2PO4(pH8)(8:2, v/v) in2min and detected by a HPLC-UV system. At different fortified concentrations, the extraction recoveries of MACs could reach89.1%with RSDs lower than12.4%. The chromatogram baseline of spiked sample was smooth after treatment by the proposed MSPE, and the response singals of6MACs were greatly enhanced due to matrix interferences being eliminated effectively. Compared with other analytical methods combining conventional SPE and HPLC-UV for determination of MACs in foodstuff samples, the LODs of the developed MSPE-HPLC-UV method was much lower, and the proposed method realized rapid, accurate and sensitive determination of multiple MACs in complex foodstuff samples.