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Magnetic Graphene-based Solid-phase Extraction Coupled with High Performance Liquid Chromatography for the Determination of Some Environmental Pollutants

Author: WangWeiNa
Tutor: WangZhi
School: Agricultural University of Hebei
Course: Analytical Chemistry
Keywords: Graphene Magnetic solid phase extraction High performance liquidchromatography Determination Neonicotinoid insecticides Triazolefungicides Chlorophenols Polycyclic aromatic hydrocarbons Phthalateesters Environmental water samples Soybean milk
CLC: O658.2
Type: Master's thesis
Year: 2013
Downloads: 134
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Abstract

Since pollutants in environmental samples are generally present in low concentrations,the preconcentration of the target analyte and reduction or elimination of the interferencesoriginally present in the samples become one of the most critical steps in the entireanalytical process. Traditional and commonly used extraction techniques are liquid-liquidextraction and solid-phase extraction. However, liquid-liquid extraction is tedious,time-consuming and needs large volumes of samples and toxic organic solvents.Solid-phase extraction procedures are considered superior to liquid-liquid extractionprocedures for their simplicity and consumption of smaller volumes of organic solvent.However, solid-phase extraction is still tedious and time-consuming. In order to overcomethese disadvantages, a new mode for solid-phase extraction, based on the use of magneticor magnetically modified adsorbents called magnetic solid-phase extraction (MSPE) hasbeen developed. The magnetic materials can be readily separated from sample solutions bythe application of an external magnetic field without the need of additional centrifugationor filtration procedures. Graphene (G) is a novel carbon-based material.It possesses manyunique features and has large surface area. As the large delocalized π-electron system of Gcan form a strong π-stacking interaction with the benzene ring, it might be also a goodadsorbent for the extraction of benzenoid form compounds. The introduction of magneticproperties into G could combine the high adsorption capacity of the G and the separationconvenience of the magnetic materials. Therefore, the magnetic G nanoparticles could havegood functionalities and performances for separation applications.In this thesis work, MSPE coupled with high performance liquid chromatography(HPLC) was explored for the determination of the neonicotinoid insecticides, triazolefungicides, chlorophenols, polycyclic aromatic hydrocarbons, phthalate esters inenvironmental water or soybean milk samples. This thesis is mainly concerned with thefollowing aspects:1. A new kind of G magnetic nanoparticles (G-Fe3O4) was prepared by chemicalprecipitation method and used as the adsorbent for the preconcentration of the fourneonicotinoid insecticides from environmental water samples. The properties of themagnetic adsorbent were characterized by scanning electron microscopy, transmissionelectron microscopy and X-ray diffraction. After the preconcentration, the adsorbent can be conveniently separated from the aqueous samples by an external magnet, and theanalytes desorbed were determinated by high performance liquidchromatography-ultraviolet detection (HPLC–UV). Various parameters affecting theextraction efficiencies such as the concentration of G-Fe3O4, the extraction time, the pHand salinity of the sample solution, and the desorption conditions were investigated. Underthe optimum conditions, the linearity of the method was in the range from0.05to50ngmL-1with the correlation coefficients (r) ranging from0.9990to0.9995and theconcentration factors for the analytes ranged between3325and4644. The limits ofdetection (LODs, S/N=3) of the method for thiamethoxam, imidacloprid, acetamiprid andthiacloprid were0.01,0.006,0.004and0.006ng ml-1, respectively. The relative standarddeviations (RSDs) varied from4.3%to7.4%(n=6). The recoveries of the method for thecompounds at spiking levels of0.5and5ng mL-1were in the range of86%-110%. Themethod has been successfully applied to the analysis of the neonicotinoid insecticides inreal water samples.2. A G-based magnetic nanocomposite was used as an effective adsorbent for thepreconcentration of some triazole fungicides in environmental water samples prior toHPLC–UV. The method, which takes the advantages of both nanoparticle adsorption andmagnetic phase separation from the sample solution, could avoid the time-consumingexperimental procedures related to the traditional solid phase extraction, such ascentrifugation and filtrations. Various experimental parameters affecting the extractionefficiencies such as the amount of the magnetic nanocomposite, extraction time, the pHvalues of the sample solution, salt concentration and desorption conditions, wereinvestigated. Under the optimum conditions, the enrichment factors of the method for theanalytes were5824,3600and4761, respectively. A good linearity was observed in therange of0.1-50ng mL-1for tebuconazole and0.05-50ng mL-1for myclobutanil andhexaconazole, respectively, with the correlation coefficients ranging from0.9992to0.9996.The LODs of the method were between0.005and0.01ng mL-1. The results indicated thatas a magnetic solid-phase extraction adsorbent, the G-based magnetic nanocomposite has agreat potential for the preconcentration of some compounds from liquid samples.3. In this part, the synthesis of G was improved by using thermal-decompositionreduction of GO in the tube heating furnace. The synthesis method was simpler, moreconvenient and more environmentally friendly. The novel G-based magneticnanocomposite (G-Fe3O4) was used as an effective adsorbent for the preconcentration ofsome chlorophenols (2-chlorophenol,3-chlorophenol,2,3-dichlorophenol,3,4-dichlorophenol and2,4,6-trichlorophenol) in environmental water samples followed byHPLC-UV detection. Various experimental parameters that could affect the extractionefficiencies, such as the amount of G-Fe3O4, the extraction time, the pH of sample solutionand the desorption conditions, were investigated. Under the optimum conditions, a good linearity existed in the range of1.0-100.0ng mL-1for all the analytes, with the correlationcoefficients (r) ranging from0.9977to0.9992. The enrichment factors of the method forthe analytes were in the range from150to183. The LODs of the method were between0.10and0.12ng mL-1. The RSDs varied from2.2%to7.5%(n=6), and the recoveries ofthe method for the analytes at spiking levels of5.0and10.0ng mL-1were in the rangefrom85.6%to107.3%.4. To enhance the stability of the G-based magnetic particles, a SiO2protectivecoating on a magnetic core was used, and a novel adsorbent, magneticmicrosphere-confined G (Fe3O4@SiO2-G), was fabricated. Then it was used for theextraction of five polycyclic aromatic hydrocarbons (fluorene, anthracene, phenanthrene,fluoranthene and pyrene) in environmental water samples prior to HPLC with fluorescencedetection. The properties and morphology of Fe3O4@SiO2-G were characterized bytransmission electron microscopy and X-ray diffraction. Various experimental parametersthat could affect the extraction efficiencies, such as the amount of Fe3O4@SiO2-G, the pHand ionic strength of sample solution, the extraction time and the desorption conditions,were investigated. Due to the high surface area and excellent adsorption capacity of theFe3O4@SiO2-G, satisfactory extraction recoveries can be achieved with only15mg of theadsorbent per250mL solution and5min extraction. Under the optimum conditions, alinear response was observed in the concentration range of5~1500ng L-1for fluorene,2.5~1500ng L-1for anthracene and15~1500ng L-1for phenanthrene, fluoranthene andpyrene with the correlation coefficients (r) ranging from0.9897to0.9961. The LODs ofthe method were between0.5and5.0ng L-1. The RSDs were less than5.6%. Therecoveries of the method were in the range between83.2%and108.2%. The resultsindicated that this novel G-based magnetic nanocomposite showed great adsorptive abilitytowards the five polycyclic aromatic hydrocarbons from environmental water samples.5. Magnetic microsphere-confined G (Fe3O4@SiO2-G) was fabricated as a noveladsorbent for the preconcentration of some phthalate esters in environmental water andsoybean milk samples prior to HPLC analysis. The properties and morphology of theFe3O4@SiO2-G were characterized by transmission electron microscopy and X-raydiffraction. Various experimental parameters that could affect the extraction efficiencies,such as the amount of Fe3O4@SiO2-G, the extraction time, the pH of sample solution andthe desorption conditions, were investigated. Under the optimum conditions, the LODs ofthe method for the compounds were between0.07and0.10ng mL-1in water samples, and0.15and0.30ng mL-1in soybean milk samples. This novel G-based magneticnanocomposite showed great adsorptive ability towards the analytes. The method has beensuccessfully applied to determining the five phthalate esters (diallyl phthalate,di-n-propyl-phthalate, benzyl butyl phthalate, dicyclohexyl-phthalate, anddiethyl-hexyl-phthalate) in environmental water and soybean milk samples. The RSDs varied from2.7%to6.1%(n=5). The recoveries of the method were in the range between87.2%and109.0%for environmental water and soybean milk samples.

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