Application Of New Sample Pre-treatment Technology In The Analysis And Detection Of Environmental Organic Pollutants

The determination of organic and inorganic contaminants in environmental matrix has been an important branch in environmental analytical chemistry. Various instrumental analysis approaches such as high performance liquid chromatography (HPLC), gas chromatography (GC), chemiluminescence, electrochemical analysis, atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) have been developed to determine the residues of organic and inorganic contaminants. However, due to fact that the concentration level of the toxic contaminants in the complex matrix is low and the chemical compositions are rather complicated, it is impossible to directly determinate the real concentration of the target compounds. So the sample preparation steps including separation, enrichment and purification of the target from the studied matrix are so critical for quantitative analysis. In some sense, the reliability of the analytical method depends on the quality of the sample pretreatment procedures, and it is of vital significance to qualitative and quantitative detection.Traditional sample pre-treatment technologies, such as liquid-liquid extraction and Soxhlet extraction, is tedious and consume large amounts of toxic and hazardous organic solvents, easy to cause secondary pollution to the environment, and can not meet the requirements of the environmental analysis. So it is necessary to develop simple, rapid, efficient and green sample pretreatment techniques to promote the development of analytical technology. The study on the sample pretreatment has become one of the hotspots in the field of environmental science. So far, lots of novel sample preparation methods including cloud point extraction (CPE), solid-phase extraction (SPE), solid-phase microextraction (SPME), liquid-phase microextraction (LPME), pressuried fluid extraction (PFE), matrix solid-phase dispersion (MSPD), Stir Bar Sorptive Extraction (SBSE) have been widely used. Among which, SPE was usually used for the pretreatment of environmental and biological samples for its high efficient enrichment, low organic solvent consumption, ease automation, diversification of operation modes and other advantages. LPME is one of the newly developed sample pretreatment techniques, and has received great attention due to its characteristics of miniaturization operation, high enrichment efficiency, high extraction speed and little reagent-consuming. As for SPE, one of the key factors affecting extraction efficiency is the choice of adsorbents. Commercial SPE adsorbents including C8, C18, Oasis HLB, graphitizede carbonb, etc have shortcomings in adsorptive selection and reusability, which led to the demand of exploring new adsorptive materials. In recent years, nanomaterials and biomaterials have attracted widespread interest in the field of SPE due to their unique structures and properties. As for LPME, the operation mode and the choice of extraction solvent are keys to the success of extraction. In this thesis, we established a series of novel analytical methods based on SPE and LPME, and investigated their application in the determination of environmental organic pollutants. It is maily composed of six chapters:The first chapter:In this chapter, we summarized the applications of novel sample preparation techniques in the field of environmental analysis.The second chapter:In this chapter, the potential use of cigarette filters (CFs) as SPE adsorbents for the preconcentration of six fluoroquinolones (FQs) antibacterial agents prior to liquid chromatography was examined. In order to find a suitable procedure for extraction of the target FQs in one single step, various parameters probably affecting the extraction efficiency including the eluent kind and volume, sample flow rate, pH of sample solution, ion strength and sample volume were systematically optimized. Under the optimized conditions, the target FQs could be easily extracted by the proposed SPE cartridge. Combination of SPE with HPLC/UV provided detection limits for different FQs of2-5ng L-1when500mL of water sample was processed. The precision of the method, expressed as relative standard deviation, ranged from4.1to6.3%for2.5μg L-1FQs. The recoveries of FQs spiked in environmental water samples ranged from76to112%. The results obtained from the proposed method demonstrated that CFs-based solid-phase extraction combined with HPLC/UV was suitable for analyzing fluoroquinolones in water samples at ng L-concentration level.The third chapter:In this chapter, the magnetic multiwalled carbon nanotubes (MMWCNTs) have been successfully prepared using one-pot solvothermal coprecipitation method, in which magnetic nanoparticles (MNPs) were deposited onto multiwalled carbon nanotubes (MWCNTs) by in situ high temperature decomposition of the magnetic precursor of iron (III) in ethylene glycol media. A novel procedure for extraction of linear alkylbenzene sulfonates (LAS) as model compound was thus developed in an off-line extraction system with detection by HPLC. In order to achieve optimal preconcentration, predominant factors that probably affected the extraction efficiency including the type and volume of eluent solvent, pH of sample solution, sorption time and temperature, ultrasonification desorption time, the content of the electrolyte (NaCl), humic acid concentration, amount of adsorbents and the volume of sample solution were systematically investigated and optimized in terms of recoveries of target analytes. Under the optimized conditions, LAS homologues could be easily extracted by the proposed magnetic SPE. On the basis of high-performance liquid chromatography separation and UV detection of LAS homologues, the favorable limits of detection (LOD) for LAS homologues were in the range from0.013to0.021μg L-1with a linear calibration range from0.5to100μg L-1(total concentration of LAS), and the relative standard deviations (RSDs) were2.4-5.6%for50μg L-1LAS (n=6), and the recoveries of LAS homologues in the spiked environmental water samples ranged from87.3to106.3%. Stability testing demonstrated that the MMWCNTs remained95.0%recovery for the target LAS even after a run of50adsorption and desorption cycles, showing their super operational stability. The MMWCNTs are promising adsorbents, suitable for the long-term repetitive sorption/desorption of target compounds in environmental water samples.The fourth chapter:In this chapter, a novel analytical method based on dispersion assisted solidification of floating organic drop LPME coulped with high performance liquid chromatography (DLPME-SFO-HPLC) was established for the determination of Sudan (I-IV) dyes in environmental water samples and food samples. Predominant factors that probably affected the extraction efficiency including the extractant and its volumn, dispersant and its volume, ionic strength, extraction time and temperature, pH of sample solution and volume of sample solution were systematically investigated and optimized in terms of recoveries of target analytes. On the basis of the experimental obtained in the optimization procedures, the optimized conditions are as follows:100μL1-dodecanol as extractant,400μL ethanol as dispersant, sample solution pH7, extraction time20min, extraction temperature70℃, ionic strength (10%NaCl, w/v). Then the optimized extraction conditions were applied to evaluate the analytical performances such as linearity, detection limits and precision of the established method. On the basis of high-performance liquid chromatography separation and UV detection of sudan dyes, the favorable limits of detection (LOD) were0.03μg L-1with a linear calibration range from0.2to500μg L-1, and the relative standard deviations (RSDs) were below10%for20μg L-1sudan (I-IV)(n=6), and the recoveries of sudan (I-IV) in the spiked environmental water samples and food samples were in the range of91.1-108.6%and92.6-106.6%, respectively. The experimental results demonstrated that the established method exhibited high recovery of Sudan dyes. As well as the proposed method is a rapid, precise, green and convenient enrichment method, therefore, can be successfully applied for the analysis of sudan dyes in aqueous environmental samples and food samples.The fifth chapter:In this chapter, cationic polymer polyethylenimine (PEI) was grafed to the surface of aminated magnetic nanoparticles through PEl-glutaradehyde cross-linking reaction and the composite adsorbent (Fe3O4/NH2/PEI) were obtained. In order to demonstrate the reliability of the synthetic method, the products were characterized by FT-IR, XRD, TGA and BET surface area. Then the adsorption capacity of the obtained nanocomposite was evaluated for LAS in aqueous solution. Different factors which may affect the adsorption capacity have been taken into account, such as the amounts of PEI, the dosage of adsorbents, pH value of medium and ionic strength. The adsorption kinetics, adsorption thermodynamics and adsorption isotherm were studied systematically. The results showed that the Fe3O4/NH2/PEI has very high affinity to LAS. The removal rate could reach to100%within3h with the initial concentration of20or50mg L-1LAS. Based on the experimental results, we could speculate that the adsorption of LAS molecules on the surface of Fe3O4/NH2/PEI at acid medium was driven by electrostatic interaction between the aminated N atoms and the sulfonic group of LAS molecules. Because of its excellent magnetic properties and adsorption properties, the adsorbent can remove LAS from aqueous solution effectively. What's more, the adsorbent can be separated from the waste water easily under extra magnet field. The represented parameters fitted using Langmuir and Freundlich adsorption models indicated that the Langmuir model effectively describes the adsorption data with larger R2, suggesting a better fit of the Langmuir isotherm with the experimental data compared to the Freundlich isotherm. The pseudo-first-order and pseudo-second-order equations were used to obtain the adsorption kinetic data. The results showed that the adsorption kinetics follows the pseudo-second-order model. The sixth chapter: In this chapter, the magnetic multiwalled carbon nanotubes (MMCNTs) were synthesized by a rapid hydrothermal method and then characterized using a series of analytical methods. The obtained magnetic nanocomposites were used to remove two fluoroquinolne antibiotics (moxifloxacin and norfloxacin) from aqueous media through static adsorption experimentals. The adsorption thermodynamics, adsorption kinetics, adsorption isotherm and effect of water quality parameter on adsorption were investigated systematically. The results obtained from adsorption kinetics turned out that the procedure of adsorption was very quickly at the first stage and then tend to slow down as the adsorption time increased. And the adsorption behavior of moxifloxacin and norfloxacin on MMWCNTs fitted the pseudo-second-order kinetics model. The adsorption isotherm of moxifloxacin and norfloxacin can well fit Langmuir model. The maximum adsorption capacity of moxifloxacin and norfloxacin on MMWCNTs were obtained at neutral pH conditions. The hydrophobic interaction between fluoroquinolne molecules and the surface of MMWCNTs dominates probably the adsorption process as well as strong π-π interaction between the benze of FQs and the surface of MMWCNTs. The fabricated magnetic nanocomposites, combining the magnetic properties of MNPs and the extremely high sorption capacity of MWCNTs, exhibited high adsorption efficiency to fluoroquinolne antibiotics and could be easily isolated from water solution after extraction. Thus, it is an excellent adsorbent and could be used as promising adsorbent for removal of other pollutants in aqueous solution.