Preparation And Application Of Ionic Liquids And Crown Ether-functionalized Ionic Liquids Coatings For Solid-Phase Microextraction

Solid phase microextraction (SPME) have attracted great attention in the field of analytical chemistry not only because it possesses solvent-free and miniaturized characteristics, but also because it helps to accomplish the sampling, extraction and concentration of trace organic compounds from soil, water and some other complicated environment in one step. The key point of this technology is the fiber coating. Development of cheap and highly efficient SPME coatings will become a tendency as the commercialized coatings share the disadvantages of thermal and chemical instability, high expense, short lifetime, and so on, though it does help to spread and develop this technology.Room temperature ionic liquids (RTILs) are called "green solvents" for their excellent dissolvability, high thermal and chemical stability, easy modification, good membrane formation ability, low vapor pressure and nontoxicity, etc. All these properties make them not only serve as selective stationary phases but also as desirable extraction media. The dual function of ionic liquids implies their theoretical potential of being used to prepare coating for SPME. Sol-gel technology has proposed as an appropriate method to immobilize organic-inorganic hybrid coatings on the outer surface of the fused-silica fiber or the inner surface of a capillary by chemical bonds under extraordinary mild conditions. If such active groups as allyl, hydroxyl or aloxyl are introduced into ionic liquids, some chemically bonded ionic liquid-based organic-inorganic coatings with perfect characteristics can be prepared by sol-gel technology through condensation reaction, free radical cross-linking reaction between these active groups and silane coupling agents.In our study, we used three alkoxyl substituted common ionic liquids, an alkoxyl and an allyl substituted crown ether functionalized ionic liquid as coating materials, and prepared a series of chemically bonded ionic liquid-based organic-inorganic coatings by sol-gel technology. The physical and chemical performances of these coatings were evaluated and the reaction mechanisms were probed. We also used the homemade ionic liquid-based coatings to detect phenolic compounds from soil. The results we get are as follows:1.Three novel alkoxyl-functionalized ionic liquids,1-(3-triethoxysiyl propyl)-3-methyl imidazolium hexafluorophosphate (TESPMIM[PF6]),1-(3-triethoxysiyl propyl)-3-methyl imidazolium tetrafluoroborate (TESPMIM[BF4]) and1-(3-triethoxysiyl propyl)-3-methyl imidazolium bis(trifluoromethanesulfony)imide (TESPMIM[N(SO2CF3)2]) were synthesized and used as selective coating materials to prepare chemically bonded ionic liquid-based organic-inorganic hybrid SPME fibers by sol-gel technology. The possible mechanism of the sol-gel process was proposed, and the successful binding of ionic liquids to the sol-gel substrate was confirmed by FT-IR spectroscopy. These ionic liquid-based sol-gel coatings have porous surface structure, high thermal stability, strong solvent resistance, wide pH application range, good coating preparation reproducibility, and special selectivity and extraction efficiency for both polar and non-polar compounds, such as phenolic environmental estrogens (PEEs), fatty acids, aromatic amines, alcohols, phthalate esters (PAEs) and polycyclic aromatic hydrocarbons (PAHs). Moreover, their characteristics, such as surface morphology, thermal stability and selectivity, were somewhat different depending on the anion type in ionic liquid structure. The TESPMIM[PF6] and TESPMIM[BF4]-coated fibers have much lower thermal stability (to300℃and285℃, respectively) than TESPMIM[N(SO2CF3)2]-coated fiber (to454℃). However, the selectivity of these two fibers is higher towards the strong polar analytes (PEEs and fatty acids), while lower towards the medium polar (alcohols) or non-polar analytes (PAHs) than that of TESPMIM[N(SO2CF3)2]-based fiber.2. Two task-specific ionic liquids containg crown ether function in their cations,1-(triethoxysily) propyl3-(6’-oxo-benzo-15-crown-5hexyl) imidazolium bis(trifluoromethanesulphonyl) imide ([TESP(Benzo15C5)HIM][N(SO2CF3)2]) and1-allyl-3-(6’-oxo-benzo-15-crown-5hexyl) imidazolium bis(trifluoromethanesul-phonyl)imide ([A(Benzo15C5)HIM][N(SO2CF3)2]) were used as selective stationary phase to prepare crown ether functionalized ionic liquid-based organic-inorganic hybrid coatings for solid phase microextraction by sol-gel technology and free radical cross-linking technology. The performance of these coatings were evaluated, the results are summarized as follows: Due to the unique properties of both ionic liquids and benzo-15-crown-5functional group, the crown ether functionalized ionic liquid-based coatings have special "bubble-like" surface structure, high thermal stability (to435℃and418℃), wide pH range (pH0-14), excellent solvent resistance and good coating preparation reproducibility (RSD<10%), They also have good selectivity and extraction efficiency for both polar and non-polar compounds, such as phenolic compounds, fatty acids, aromatic amines, alcohols, phthalate esters and polycyclic aromatic hydrocarbons. 3. A novel ultrasonic extraction-solid phase microextraction-gas chromatography (UE-SPME-GC) method with sol-gel-derived TESPMIM[N(SO2CF3)2]-OH-TSO fiber was developed for the determination of phenolic compounds in soil. The parameters affecting the extraction efficiency of UE (extraction solvent, extraction time) and SPME (the volume of the solvent extracts added, extraction temperature, extraction time, salt concentration, matrix pH and desorption time were optimized. Under the optimum conditions, the proposed method was used for the detection of phenolic compounds in two agricultural soil samples from EZhou and QingShan Iron and Steel Corporation. The results were quite satisfactory. The linear ranges of the calibration curve were about two orders of magnitude. The detection limit was low, ranging from8.5ng g-1to120.2ng g-1. The precision (n=5) was good, with the relative standard deviation values from1.8%to9.8%. The recoveries for these two soil samples were from72.25%to119.83%and75.59%to111.82%, respectively.