The Preparation Of Nanometer-sized Magnetic Materials And Their Application To Trace Elements And Their Species Analysis

The analysis of trace/ultratrace elements and their species in environmental and biological samples is significant for assessment of environmental pollution, food security and human health. Inductively coupled plasma optical emission spectrometry/mass spectrometry (ICP-OES/MS) is considered to be one of the most powerful techniques for elemental analysis because of its high sensitivity, wide dynamic linear range, multi-element capability etc. However, when the conventional ICP-OES/MS was employed for real-world sample analysis, it still suffered from some problems:(1) The physical and chemical state of some samples may not allow their direct determination;(2) The concentration of target elements is very low and the sample matrix is often complex, which will affect the accuracy of the analytical results.(3) ICP cannot distinguish different species of the same element. A sample pretreatment step, which can separate the analytes from the matrix and preconcentrate them before their measurement, can solve these problems. Among various sample pretreatment techniques, solid phase extraction (SPE) has the advantages of high enrichment factors, rapid phase seperation, low organic solvent consumption, simple operation, as well as easy-to-automate and has been become one of the most commonly used sample pretreatment techniques for elemental analysis. In SPE techniques, adsorbent material plays a key role, because it determines the selectivity and sensitivity of the analytical method. Therefore, the exploration and application of new and excellent adsorbents is receiving a great attention in present SPE study. Due to their unique properties, nanometer materials, including metal oxide nanoparticles, carbon-based nanometer materials (eg. graphene oxide) and magnetic nanoparticles, have exhibit excellent performance in analysis of elements and their species. They also have some drawbacks in application:firstly, metal oxide nanoparticles is lack of selectivity to elements and their species. Secondly, it is hard to directly apply graphene oxide as an adsorbent due to its high hydrophilicity. Thirdly, the type of magnetic nanoparticles for elemental speciation is limited. The aim of this dissertation is to explore the novel nanometer-sized materials (modified nanometer-sized ZrO2, graphene oxide-based composite materials and magnetic nanoparticles); to investigate their adsorption performancc to elements and their species and to develop new methods of SPE/Magnetic SPE (MSPE) coupled with ICP-OES/MS for the analysis of elements in environmental samples. The major contents of this dissertation are described as follows:(1) A novel adsorbent was synthesized by grafting calconcarboxylic acid (CAA) dynamically to nanometer-sized zirconia (ZrO2) and was characterized with transmission electron microscopy (TEM), nitrogen adsorption instrument and Fourier transform infrared spectroscopy (FT-IR). By using CAA modified nanometer-sized ZrO2as micro-column packing material, a new method of flow injection (FI) SPE on-line preconcentration coupled with ICP-OES was developed for simultaneous determination of trace metals (Cd, Co, Cu, Ni and Pb) in environmental water samples. The experimental parameters including pH, sample flow rate and volume, elution volume and flow rate and coexisting ions on the extraction of the target analytes were investigated, and the optimal experimental conditions were established. Under the optimized operating conditions, the limits of detection (LODs) of this method for Cd, Co, Cu, Ni and Pb were0.16,0.04,0.28,0.22, and0.95ng mL-1, with the relative standard deviations (RSDs) of2.2,3.0,4.5,4.1and7.7%(n=7, c=10ng mL-1), respectively. An enrichment factor of10and sampling frequency of12h-1were obtained by using a loading time of200s and elution time of30s. The proposed method was validated by analysis of the target metals in Certified Reference Materials of GSBZ50009-88environmental water and real-world natural water samples.(2) Graphene oxide-silica (GO-silica) composite coating was prepared for hollow fiber solid phase microextraction (HF-SPME) of trace Mn, Co, Ni, Cu, Cd and Pb followed by on-line ICP-MS detection. The structure of the prepared graphene oxide and GO-silica composite were studied and elucidated by atomic force microscopy (AFM), TEM, FT-IR and X-ray photoelectron spectroscopy (XPS), respectively. The GO-silica composite coated hollow fiber was characterized by scanning electron microscope (SEM), and the results show that the GO-silica composite coating possessed a homogeneous and wrinkled structure. Various experimental parameters affecting the extraction of the target metal ions by GO-silica composite coated HF-SPME have been investigated carefully. Under the optimum conditions, the LODs (3σ) for Mn, Co, Ni, Cu, Cd and Pb were7.5,0.39,20,23,6.7and28ng L-1and the RSDs,(cMn, Co, cd=0.05μg L-1, CNi,Cu,Pb=0.2μg L-1, n=7) were7.2,7.0,5.6,7.3,7.8and4.6%, respectively. The accuracy of the proposed method was validated by the analysis of Certified Reference Material of GSBZ50009-88environmental water and the determined values were in a good agreement with the certified values. The proposed method has been successfully applied for the determination of trace metals in real environmental water samples with recoveries ranging from85to119%.(3) L-cysteine functionalized magnetic mesoporous sorbent (L-MMS) was prepared and applied to MSPE of trace heavy metal ions (Cu, Cd, Hg and Pb) in environmental water samples followed by ICP-MS detection. The prepared L-MMS was characterized by TEM and nitrogen adsorption instrument and UV-vis spectrophotometer. The BET surface area and the thiols amounts of L-MMS and L-cysteine functionalized magnetic sorbent (L-MS) were investigated. The adsorption capacity of L-MMS and L-MS for Cu, Cd, Hg and Pb were studied. Various parameters affecting L-MMS MSPE of target metal ions have been investigated. Under the optimized conditions, the LODs (3σ) for Cu, Cd, Hg and Pb were8.2,1.6,0.93and10pg mL-1and the RSDs (cCd, Hg=0.02ng mL-1, cCu, Pb=0.1ng mL-1, n=7) were7.8,6.7,5.1and8.6%, respectively. The proposed method has been successfully applied for the determination of trace metals in sewage water and natural water samples with recoveries ranging from79.1to119.1%. The developed method has the advantages of high enrichment factors, simplicity, rapidity, and can be directly applied in analysis of Cu, Cd, Hg and Pb in water samples without additional filtration or centrifugation. (4) Fe3O4@SiO2@polyaniline-graphene oxide (PANI-GO) composite was prepared firstly through a simple noncovalent method and applied to MSPE of trace rare earth elements (REEs) in tea leaves and environmental water samples followed by ICP-MS detection. The prepared Fe3O4@SiO2@PANI-GO composite was characterized by TEM and vibrating sample magnetometer. Various parameters affecting Fe3O4@SiO2@PANI-GO MSPE of target REEs have been investigated. Under the optimized conditions, the LODs (3σ) for REEs were in the range of0.04-1.49ng L-1and the RSDs (c=20ng L-1, n=7) were1.7-6.5%. The proposed method was validated by analyzing a Certified Reference Material of GBW07605tea leaves and successfully applied for the determination of trace REEs in tea leaves and environmental water samples. The developed Fe3O4@SiO2@PANI-GO MSPE-ICP-MS method has the advantages of simplicity, rapidity, good selectivity, high sensitivity and is suitable for the analysis of trace REEs in samples with complex matrix.(5) A novel method of Fe3O4@SiO2@PANI MSPE coupled with ICP-MS was developed for the speciation of inorgnic Se and Te in environmental waters. The procedure is based on that the prepared Fe3O4@SiO2@PANI can selectively extract Se (IV) and Te (IV), while Se (VI) and Te (VI) cannot be retained on Fe3O4@SiO2@PANI. The adsorption mechanism was investigated preliminarily. Various parameters affecting Fe3O4@SiO2@PANI MSPE of Se (IV) and Te (Ⅳ) have been investigated. Under the optimized conditions, the LODs (3σ) for Se (IV) and Te (IV) were5.3and1.2pg mL-1and the RSDs (c Se(Ⅳ)=100pg mL-1, c Te (Ⅳ)=10pg mL-1n=7) were3.8and8.0%. The enrichment factors of the proposed method is100-folds. The proposed method was successfully applied to the speciation of inorgnic Se and Te in environmental water samples. The developed MSPE-ICP-MS method possesses the advantages of low cost, high enrichment factor, rapidity and can simultaneous analysis of inorgnic Se and Te species in real-world samples.(6) Al3+immobilized Fe3O4@SiO2@iminodiacetic acid (IDA) was prepared and its extraction performance for gold nanoparticles (AuNPs) and gold ions (Au ions) was investigated. It was found that AuNPs and Au ions could be simultaneously retained on the prepared adsorbent and their separation was achieved by sequential elution of Au ions and AuNPs with Na2S2O3and NH3·H2O, respectively. Based on it, a novel strategy by coupling MSPE with ICP-MS was developed for the speciation of AuNPs and Au ions in environmental water samples. Various experimental parameters affecting MSPE of AuNPs and Au ions have been investigated carefully. Under the optimized conditions, the LODs (3σ) for Au ions and AuNPs were0.39and0.31pg mL-1and the RSDs (c=20pg mL-1, n=7) were3.9and4.9%, respectively. AuNPs in a size range of14-140nm and with different coatings, including citrate,11-mercaptoundecanoic acid (MUA), polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB), could be quantitatively determined by the proposed method. And the size and shape of the AuNPs were found to be kept unchanged during the extraction process, thus the elution solutions could be directly introduced into ICP-MS without digestion. The developed MSPE-ICP-MS method has been applied to the analysis of AuNPs in natural water, sewage water and even sea water samples and Au ions in natural water samples with satisfied results. Compared with the established methods for metal nanoparticles analysis, the developed method is more sensitive, faster, easier-to-operate, no digestion required, and provides more valuable information.