Preparation And Application Of Novel Ionic Liquids-Based Coatings For Solid-Phase Microextraction

Solid-phase microextraction (SPME), as a fast, solvent-free alternative to conventional sample extraction techniques, was introduced and developed by Pawliszyn and co-workers in the early 1990s. It has been used for the fast and accurate analysis of trace pollutants in complicated environmental medium, such as soil and water samples. The key part of the SPME technique is the fiber coating. To date, commercial coatings suffered from limited varieties, relatively low thermal and chemical stability, have limited the development of SPME techniques to a certain extent. Therefore, developing high selective, stable and effective sorbent coatings is very necessary for future advancements in SPME technology.Room temperature ionic liquids (RTILs), formerly known as liquid organic, molten salts, or fused salts, are a class of nonmolecular ionic solvents with low melting points. Most widely studied ILs are comprised of bulky, asymmetrically substituted N-containing organic cations (e.g., N-alkylimidazolium, N-alkylpyridinium, tetraalkylammonium or tetraalkylphosphonium) in combination with various anions, ranging from simple inorganic ions (e.g., halides, hexafluorophosphate [PF6], tetrafluoroborate [BF4]) to more complex organic species (e.g., trifluoromethylsulfonate; bis[(trifluoromethyl) sulfonyl]amide [(CF3SO2)2N]; trifluoroethanoate). They have negligible vapor pressure at room temperature, have high thermal stability, possess relatively high viscosity and thus good wetting and film-forming ability, and are capable of undergoing multiple solvation interactions with various organic molecules and metal ions. Moreover, their physical and chemical characteristics, such as hydrophobicity, separation selectivity, viscosity and thermal stability, can be tuned by the alternation of the substitutive group on the cation or the combined anion. These unique properties of ILs merit their consideration both as "green" extraction solvent in sorptive microextraction techniques and selective stationary phases in analytical separation.Therefore, ILs have become favourable candidates for SPME coating material.In this work, hydroxylethyl and allyl functionalized ILs were used as selective coating materials to prepare chemically bonded IL-based SPME fibers by sol-gel method and free radical cross-linking technology. The practical applicability of these IL-based sol-gel coatings were evaluated through the analysis of phenolic environmental estrogens (PEEs) and aromatic amines in two real water samples as well as phthalate acid esters (PAEs) in agricultural film. The results are summarized as follows:1. Two hydroxylethyl-functionalized ILs, 1-(2'-hydroxylethyl)-3-methylimidazolium tetrafluoroborate (HEMIM[BF4]) and 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (HEMIM[N(SO2CF3)2]) were first used as selective stationary phase to prepare ILs-hydroxyl-terminated silicone oil (OH-TSO) hybrid organic-inorganic coatings for SPME by sol-gel technology. The underlying mechanisms of the sol-gel reaction were proposed and the successful binding of ILs to the sol-gel substrate was confirmed by FT-IR spectra. The performance of these two ILs-based coatings was somewhat different, depending on the type of anions in ILs structure. Firstly, in contrast to HEMIM[N(SO2CF3)2]-OH-TSO coating, the pores on the surface of HEMIM[BF4]-OH-TSO coating are arranged more orderly and uniformly with a smaller size. Secondly, the HEMIM[N(SO2CF3)2]-based fibers had much higher thermal stability compared with the HEMIM[BF4]-based fibers. Thirdly, the extraction efficiency of HEMIM[BF4]-OH-TSO fiber towards PEEs and aromatic amines was superior to that of HEMIM[N(SO2CF3)2]-OH-TSO fiber, and OH-TSO fiber without ILs. Moreover, these ILs-based SPME fibers had wonderful solvent resistance, wide useable pH range and good coating preparation reproducibility. Efficient analysis of aromatic amines with headspace SPME-GC was achieved using sol-gel-derived HEMIM[N(SO2CF3)2]-OH-TSO fiber. The method showed linear response over three to four orders of magnitude. The limits of detection were very low, ranged between 0.0063 and 0.2013μg/L. The relative standard deviation values were below 7% and the recovery varied from 87.4% to 111.5%.2. Two allyl-functionalized ILs, 1-allyl-3-methylimidazolium hexafluorophosphate (AMIM[PF6]) and 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMIM[N(SO2CF3)2]) were first used as selective coating materials to prepare chemically-bonded ILs-based organic-inorganic hybrid SPME fibers with the aid of y-methacryloxypropyltrimethoxylsilane as bridge by sol-gel method and free radical crosslinking technology. The underlying mechanisms of the sol-gel reaction were proposed and the successful binding of these functional ILs to the sol-gel substrate was confirmed by FT-IR spectroscopy. These ILs-bascd sol-gel coatings have porous surface structure, high thermal stability, wide range pH stability, strong solvent resistance, long lifetime, and good coating preparation reproducibility. They also have high selectivity and sensitivity towards strong polar PEEs and aromatic amines due to the strong electrostatic, hydrogen bonding andπ-πinteractions provided by the special molecular structure of these imidazolium ILs. Moreover, their characteristics are somewhat different, depending on the type of anions in ILs structure. The practical applicability of these ILs-based sol-gel coatings was evaluated through the analysis of PEEs in two real water samples collected from South Lake as well as sewage drainage outlet along the lake in Wuhan, China. The detection limits were quite low, varying from 0.0030 to 0.1248μg/L. The linearity was very good in the range of 0.1 to 1000μg/L for most analytes, and the relative standard deviation values were below 6%. The relative recoveries were between 83.1 and 104.1% for lake water, and between 89.1 and 97.1% for sewage drainage outlet water.3. A novel crown ether functionalized IL, 1-allyl-3-(6'-oxo-benzo-15-crown-5 hexyl) imidazolium hexafluorophosphate ([A(benzo15C5)HIM][PF6]) was synthesized and used as selective stationary phase to prepare task-specific IL-based SPME fibers by sol-gel method and free radical cross-linking technology. The underlying mechanism of the sol-gel reaction was proposed and the successful chemical bonding of the crown ether functionalized IL to the formed hybrid organic-inorganic copolymer coating was confirmed by FT-IR spectroscopy. The performance of this in situ created crown ether functionalized IL-based SPME fibers was investigated in detail. The coating has porous surface structure, stable performance in high temperature (to 340℃) and in different solution (water, organic solvent, acid and alkali) and good coating preparation reproducibility. In contrast to the sol-gel derived 1-allyl-3-methyl imidazolium hexafluorophosphate IL coating prepared with the identical procedure, the extraction perfonnance of this newly developed sol-gel crown ether functionalized IL coating was superior for alcohols, PAEs, PEEs, fatty acids and aromatic amines due to the introduction of benzo-15-crown-5 functional group in IL structure. Moreover, it was shown to provide higher or comparable extraction efficiencies for most analytes studied than did the commercial PDMS, PDMS/DVB and PA fibers.4. A detection method using ultrasonic extraction-SPME combined with gas chromatography with [AMIM][N(SO2CF3)2]-OH-TSO coated fiber was developed for the determination of eight endocrine disruptors—PAEs in agricultural plastic film including Dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), diamyl phthalate (DAP), diisooctyl phthalate (DIOP), di-n-octyl phthalate (DnOP), dinonyl phthalate (DNP), didecyl phthalate (DDP). The fiber shows wonderful extraxtion efficiency for the tested compounds than did the commicial PDMS, PDMS/DVB and PA fibers. This test method is simple, rapid and economic and the environmental toxicity is relatively small. The method showed linear response over three to four orders of magnitude, and limits of detection ranged between 2.5 and 62.9 ng/L. The relative standard deviation values obtained were <10%. Recoveries were in the ranges 90.2%～111.4% in all the samples.