Preparation And Application Of Novel Solid-phase Microextraction Coating For The Analysis Of Environmental Samples

Solid phase microextraction (SPME) is novel sample preparation technique, which integrates sampling, clean-up, concentration and sample introduction into one step. SPME technique has many advantages such as solvent free, efficiency, rapidness and convenience, and has been widely applied in many areas of analytical chemistry. The fiber coating is the heart of SPME technique, and it determines sensitivity of analysis, selectivity of extraction, repeatability of determination and fiber durability. However, current SPME fiber coatings still have some disadvantages such as insufficient thermal, chemical and mechanical stability, low extraction efficiency and selectivity. In order to overcome these drawbacks, we have developed several novel SPME coatings with enhanced physical and chemical stability and good extraction performance via sol-gel technology, free radical polymerization and in situ solvothermal reaction, and investigated the extraction mechanism of the coatings. These coatings were applied to extract persistent organic pollutants in environmental samples. The contents of this research were summarized as follows:1. An octadecyl-functionalized SPME fiber was prepared by sol-gel technology with an anodized Ti wire as the substrate and dimethyloctadecyl [3-(trimethoxysilyl)propyl]ammonium chloride (C18-TMS) and tetraethoxysilane (TEOS) as sol-gel precursors. The anodized Ti wire has high mechanical strength and has numerous titanol groups on its surface for sol-gel reactions, consequently offering better performances than the commercial fragile fused silica substrate. The C18-TMS/TEOS sol-gel coated fiber has good thermal stability and stability against organic solvents. There is no loss in the performance after100cycles of exposure to acetonitrile and high temperature (300℃) in turn. The developed fiber with a very thin (ca.2μm) coating thickness exhibits comparable or even superior extraction capability relative to the commercial100μm polydimethylsiloxane (PDMS) fiber. The proposed method was successfully applied in the analysis of environmental water samples.2. A mixed-mode SPME coating was designed aiming to extract perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). The mixed-mode coating was prepared by chemical bonding dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride and3-(trimethoxysilyl)-1-propanamine, the sol-gel precursors, on an anodized Ti wire via sol-gel technology. The prepared mixed-mode coating showed excellent thermal and organic solvent stability due to the covalent bonding between the coating and Ti wire substrate. The proposed coating exhibited significantly higher extraction efficiency than that of the commercial100μm polydimethylsiloxane fiber and85μm polyacrylate fiber due to the synergistic extraction effects of the coating functional groups.3. An organic-inorganic hybrid polymeric coating was prepared on an anodized and derived Ti wire by free radical polymerization. A polyhedral oligomeric silsesquioxane (POSS) reagent containing methacryl substituent groups was used as an organic-inorganic hybrid cross-linker, and copolymerized with methyl methacrylate (MMA) in the glass capillary to fabricate the hybrid coating. The prepared fiber can be easily withdrawn from the glass capillary mold by controlling the polymerization conditions, especially polymerization solvent. A homogeneous and porous coating with thickness of about100μm was achieved using ethanol as polymerization solvent at the mass ratio of MMA to POSS as1:0.5. High chemical and mechanical stability, as well as excellent durability for more than100times extractions with almost undiminished extraction efficiency were achieved due to the chemical immobilization and crosslinked hybrid coating. The proposed coating was successfully applied in the analysis of PAHs in environmental samples.4. A novel polymeric ionic liquid-based SPME coating was prepared on the surface of an anodized Ti wire using1-hexyl-3-vinylimidazolium hexafluorophosphate as monomer and POSS nanoparticles as hybrid crosslinker via free radical polymerization. The proposed fiber coating exhibited high mechanical stability due to the chemical bonding between the coating and the Ti wire surface. Using POSS as hybrid crosslinker increased the crosslinking degree of the polymeric ionic liquid coating, which enhanced the organic solvent resistance of the coating. The proposed coating was applied to effectively extract perfluorinated compounds in aqueous samples by direct immersion SPME coupled with HPLC analysis.5. A zeolitic imidazolate frameworks (ZIF-7) crystal film coating was fabricated on the surface of Ti wire etched by hydrofluoric acid via solvothermal reaction. The presence of sodium formate played an important role in the formation of ZIF-7crystal film, because it can enhance the heterogeneous nucleation of ZIF-7crystals and promote intergrowth of ZIF-7crystal film and then compact and homogeneous ZIF-7crystal film was obtained. The ZIF-7crystal film coating had good water stability and could be directly immersed into aqueous samples for the extraction of PAHs. The ZIF-7crystal film coating showed high extraction efficiency for PAHs due to hydrophobic interaction and π-π interaction between the organic ligands of ZIF-7crystals and PAHs. A SPME-HPLC method based on the ZIF-7crystal film coating was established after optimizing the factors affecting the extraction efficiency.