| Room temperature ionic liquids (RTILs) are ionic compounds whose melting points are around ambient temperature. They are usually composed of asymmetrical organic cations and anions. Since their properties can be readily tuned by changing the composition of cation or anion, they are called "designer solvents". On the other hand, they are also called "green solvents" due to its negligible vapor pressure, non-volatility, incombustibility and low toxicity. Based on their unique physicochemical properties, ILs have become an attractive subject in chemistry, and have been widely used as electrolyte materials, novel catalysts and extraction materials, as well as for stationary phase of chromatography, etc.The negligible vapor pressure, suitable viscosity, wide liquid range and good solubility suggest that ionic liquids has a great potential for application as stationary phase of gas chromatography. In the study of ILs stationary phase, it has been found that, (1) The ionic liquids composed of small molecular without polymerization could not possess high column efficiency and thermal resistance; (2) The polymeric stationary phases could be made from vinyl IL by in-column polymerization reaction, but the procedure was complicated and time consuming; (3) The ILs mixing with commercial polysiloxane stationary phases provided excellent wetting ability on inner wall of capillaries. However, the durability of the physical mixture seemed to be doubted because of the significant difference between the chemical and physical natures of ILs and polysiloxane stationary phases. Thus, feasible synthesis method is still crucial in the research of stationary phases comprising of ionic liquids.In this paper, the method of ionic liquid bonding with polysiloxane via quaterisation was proposed to prepare a kind of stationary phase with well coating, durability and high thermal stability. Two kinds of ionic liquid ([PSOMIM][C1] and [PSOMIM][NTf2]) were synthesized, then they were used as stationary phase for gas chromatography and their chromatographic performances were discussed, respectively. Since the unique selectivity of ionic liquid bonded polysiloxane stationary phase, [PSOMIM][NTf2] was also used as stationary phase for fast GC. The impacting factors to the speed of analysis were studied from the length, diameter and film thickness of columns. Moreover, in order to explore the separation of chiral samples, several chiral ionic liquids using cheap and accessible natural chiral compounds were synthesized, and the chromatographic performances were discussed when they were used as the stationary phase for GC. The main contents in this paper are summarized as follows:1. ReviewFirstly, the development of capillary columns for gas chromatography was presented. Then, the composition and property of ionic liquids were summarized. Moreover, the application of ionic liquids in electrochemistry, extraction separation, capillary electrophoresis and chromatography are reviewed. The development of ionic liquids as stationary phases for gas chromatography was introduced in detail.2. The synthesis and characterization of ionic liquid bonded polysiloxanesIonic liquid bonded polysiloxanes were synthesized via quaterisation between y-chloropropyl-polysiloxane and 1-methylimidazole. Firstly, y-chloropropyl-polysiloxane was prepared through hydrolyzation and polymerization of several silane monomers. Two types of ionic liquid bonded polysiloxanes were synthesized:one using Cl- as the anion ([PSOMIM][C1]), the other using [NTf2]-as anion ([PSOMIM][NTf2]), the content of imidazolium unit in ionic liquid polysiloxanes was about 10% or 30%. The structures of these products were confirmed by 1H NMR and FT-IR. The thermogravimetric (TG) tests were used to evaluate the thermo-stability of the products. The results indicated that [PSOMIM][C1] began to decompose slightly at 220℃, but [PSOMIM][NTf2] was stable before 380℃.3. The performance of ionic liquid polysiloxane ([PSOMIM][C1]) as stationary phase for GCIonic liquid bonded polysiloxane [PSOMIM][C1] (10%) was used as stationary phase for gas chromatography. The column efficiency was measured to be about 4000 plates/m (k= 3.55,105℃, naphthalene). Then, the interaction between ionic liquid and solutes were studied employing the method of Rohrschneider-McReynolds constants and solvation parameter model. It was found that hydrogen bond basicity was the primary character of the ionic liquid bonded polysiloxane. Furthermore, the chromatographic performances of stationary phases were evaluated by Grob reagent and some aromatic positional isomers, and they were compared with that of DB-1 column. The result showed that the "dual nature" of ionic liquid was remained, though the content of bonded IL groups was at low level. Moreover, a series of homologous compounds (like amines, phenols and polycyclic aromatic hydrocarbons etc.) were separated well on [PSOMIM][C1] column. All of these results demonstrated the great potential of this kind of stationary phase in application.4. The performance of ionic liquid polysiloxane ([PSOMIM][NTf2]) as high temperature stationary phase for GCIonic liquid bonded polysiloxane (30%) was used as stationary phase for gas chromatography. The column efficiency was about 4776 plates/m (k= 3.64,110℃naphthalene). The interactions between ionic liquid and solutes were also studied by solvation parameter model and the influence of anion was discussed. It was found that the hydrogen bond basicity of [PSOMIM][NTf2] was obviously lower than that of [PSOMIM][C1] under the test conditions. In addition, the separation of some isomers and compounds with high boiling-point showed that anions have significant influences on the thermal stability of the IL bonded polysiloxanes. Furthermore, the good selectivity for analytes in wide range of polarity such as fatty acid methyl esters (FAMEs), polychlorinated biphenyls (PCBs) and aromatic amines suggested that [PSOMIM][NTf2] had a great potential in the high temperature and highly selective GC.5. Ionic liquid bonded polysiloxnes used as stationary phase for fast GCOwing to the unique selectivity of ionic liquid stationary phase, the ionic liquid bonded polysiloxane was used as stationary phase for fast GC. In this chapter, fused-silica capillary tubes (3.0 m×0.075 mm I.D.) were adopted to prepare the micro-columns. In order to investigate the influence of length and inter diameter of the column on analysis time, the conventional columns (8.0 mx0.25 mm I.D.) were also prepared for comparison. The separation of some isomers and homologous compounds suggested that, the analysis time could be reduced significantly without obvious loss of resolution through shortening the length and reducing the internal diameter. On the other hand, two micro-columns with different film thickness were tested to study the influence of film thickness. The results showed the analysis rate could increase two to four folds for various samples tested while the film thickness reduced from 0.075 to 0.056μm.6. Chiral ionic liquids used as stationary phase for GCThree types of chiral ionic liquids (CILs) were synthesized from natural products, amino acids and menthol, and used as stationary phases for GC. The alanine and glutamic acid were transferred into ionic liquids with chiral center at cation moiety and anion moiety, named [BAlaIM]Br and [BMIM][Glu], respectively. Then, the CILs were mixed with [PSOMIM][NTf2] to prepare chiral stationary phases and applied to GC. The results showed the column efficiency was about 3200 plates/m when the content of [BAlaIM]Br was 50%(mass percent) in the mixed stationary phase and CILs were beneficial to the selectivity towards some positional isomer tested. Among the three CILs, [BAlaIM]Br offered better selectivity for such enantiomers as carvone and citronellal, and the CIL prepared from menthol ([MMenIM][NTf2]) was better for enantiomers of ethyl lactate. |
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