| Recently, it has attracted the worldwide concern that the environmental issues are getting more and more serious. Researches on water, atmosphere and food environment are developing rapidly. Meanwhile, nanomaterials have received wide attention due to their unique properties and promising applications. Sample pretreatment techniques based on novel nanomaterials have been largely used in separating and analyzing specific environmental pollutants. Magnetic nanomaterials, which combine the double characteristics of magnetic response and nanoparticles, can be applied as magnetic solid-phase extraction adsorbents. Compared with traditional sample pretreatment techniques such as solid-phase extraction, solvent extraction and ultrasonication-assisted extraction, magnetic solid-phase extraction simplifies sample pretreatment process greatly, and makes the phase separation much easier.The contaminations in environmental matrices are mostly widely distributed, remaining in low level, complexly composed, and influenced by co-existence and matrix. Therefore, designing a sample pretreatment method which aims at specific analytes can effectively concentrate trace components, and consequently increase the method sensitivity and decrease the limit of detection. This dissertation mainly studied and developed solid-phase extraction techniques based on functionalized magnetic nanomaterials, prepared novel magnetic hybrid nanomaterials and magnetic mesoporous nanomaterials, and finally applied them to the selective enrichment and analysis of small molecule pollutants in real environmental samples. The detailed abstract of research work and its results are as follows.In chapter 1, it summarized the applications of solid-phase extraction technique in sample pretreatment of environmental systems and the research progresses of two kinds of magnetic nanomaterials on environmental sample analysis. Chapter 1 firstly introduced several modes of solid-phase extraction techniques, and then described the main applications of magnetic solid-phase extraction to different kinds of environmental pollutants. Combined with recent developments in magnetic hybrid nanomaterials and magnetic mesoporous nanomaterials, it expounded solid-phase extraction techniques based on functionalized magnetic nanomaterials in environmental analysis. Finally, the purpose and significance of this dissertation were discussed.In chapter 2, magnetic multiwalled carbon nanotubes were synthesized through a facile hydrothermal process, and then successfully used as magnetic solid-phase extraction sorbents for the determination of p-hydroxybenzoates in beverage. The prepared magnetic multiwalled carbon nanotubes presented both satisfactory superparamagnetism and strong capacity of absorption, with magnetic Fe3O4 beads of 200 nm average diameters decorated at either ends of the tubes. The hybrid nanocomposites showed a high efficiency in the extraction and enrichment of p-hydroxybenzoates via π-π stacking of targeted molecules onto the polyaromatic composed surface of multiwalled carbon nanotubes. By using an external magnetic field, p-hydroxybenzoates adsorbed on magnetic multiwalled carbon nanotubes could be rapidly isolated in only 30 s, and subsequently analyzed by liquid chromatography-diode array detector (LC-DAD) after the elution with organic solvents. Extraction conditions such as eluting solvent, the amounts of magnetic sorbents added, pH values, adsorption and desorption time were investigated and optimized to achieve the best effect. Method validations including linearity, detection limit, and precision were also studied. The linearities were in the wide range of 0.05-500 g/mL with correlation coefficients higher than 0.9983 for all p-hydroxybenzoates. The limits of detection were all less than 20 ng/mL. Acceptable RSDs were achieved within 5-8% for all analytes. The results indicated that the proposed method based on magnetic multiwalled carbon nanotubes as magnetic solid-phase extraction absorbents was rapid, efficient, and convenient for the analysis of targeted p-hydroxybenzoates in beverage samples.In chapter 3, it worked on a new exploration of the application of magnetic multiwalled carbon nanotubes as magnetic solid-phase extraction absorbents. It proposed a novel method based on matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for the efficient and high-throughput determination of the environmental pollutant of crotonaldehyde, which employed magnetic multiwalled carbon nanotubes synthesized in chapter 2 as adsorbent and matrix for MALDI-TOF-MS. Ctotonaldhyde was derived by 2,4-dinitrophenylhydrazine first followed by magnetic solid-phase extraction process and high-throughput determination. The peak of [M+Na]+ion of ctotonaldhyde derivatives in MS spectra was detected for all analysis. The crotonaldehyde derivatives could be detected at the limit concentration of 10 ng/mL at the positive ion mode and the S/N ratio reached 552.3. The reproducibility of the enrichment process was evaluated to be 11.0%. Due to the large surface area, strong interaction force and excellent inherent properties, magnetic multiwalled carbon nanotubes showed satisfactory ionization and enrichment performance for the enrichment and ionization of crotonaldhyde by MALDI-TOF-MS.In chapter 4, phenyl group-functionalized magnetic mesoporous microspheres were synthesized through a facile one-pot co-condensation approach, and then developed as solid-phase extraction sorbents for the enrichment and analysis of acetaldehyde in mainstream cigarette smoke. The prepared nanomaterials possessed abundant silanol groups in the exterior surface and numerous phenyl groups in the interior pore-walls, as well as a large surface area (273.5 m2/g) and uniform mesopores (3.3 nm). Acetaldehyde in mainstream cigarette smoke was collected in water and derivatizated with O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine. The formed acetaldehyde oximes were extracted and enriched by the prepared adsorbents via π-π interactions and subsequently analyzed using GC-MS. Extraction conditions such as amounts of sorbents, eluting solvent, adsorption and desorption time were investigated and optimized to achieve the best efficiency. Method validations including linearity, recovery, repeatability, and limit of detection were also studied. It was found that the suggested methodology provided a low detection limit of 0.04 mg/mL, good recovery of 88-92%, intra-day and inter-day RSD values of 4.5% and 10.1%, and linear range of 0.25-4 mg/mL (R2=0.999). The results demonstrated that the new method based on phenyl-functionalized magnetic mesoporous microspheres could achieve the enrichment and analysis of acetaldehyde in tobacco.In chapter 5, it designed novel raisin-bread sandwich-structured magnetic graphene/mesoporous silica composites with C18-modified interior pore-walls. The nanoparticles were synthesized by coating mesoporous silica layers onto each side of magnetic graphene through a surfactant-mediated co-condensation sol-gel process. The functionalized nanocomposites possessed marvelous properties of extended plate-like morphology, fine water dispersibility, high magnetic response, large surface area (315.4 cm2/g), uniform pore size (3.3 nm) and C18-modified interior pore-walls. Several kinds of phthalates were selected as model analytes to systematically evaluate the performance of adsorbents in extracting hydrophobic molecules followed by gas chromatography-mass spectrometry (GC-MS) analyses. Various extraction parameters, including pH value of sample solution, amounts of adsorbents, adsorption time, species and volume of eluting solvent, and desorption time were optimized. The anti-interference ability to macromolecular proteins was also investigated. Under the optimal conditions, C18-functionalized magnetic graphene/mesoporous silica composites were successfully applied to analyzing phthalates in environmental water samples. |
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