Ionic Liquids Used to Assist a Metallomesogen as Gas Chromatography Stationary Phase and Coated on a Fiber for Solid Phase Microextraction
Date Issued
2009
Date
2009
Author(s)
Huang, Kuan-Pin
Abstract
A metallomesogen of a polycatenar oxazoline copper(II) complex, [Cu(S-C12)2], that exhibited a columnar mesophase with a helical organization was prepared and employed as the stationary phase for GC separation, demonstrated on polycyclic aromatic hydrocarbons (PAHs) as model compounds. To introduce the mesogen into the capillary column, an ionic liquid (BeMIM-TfO) was used as the vehicle. The results of thermal analyses and UV-vis spectroscopy indicated that some beneficial interactions occurred between the metallomesogen and the ionic liquid. Various parameters affecting the separation efficiency were studied. Different ratios of BeMIM-TfO and Cu(S-C12)2 (1:0, 1:1, 1:2 and 1:3 (w/w)) were tested for the separation of the PAHs. As the amount of Cu(S-C12)2 increased, complete separation could be achieved. The stationary phase with a ratio of 1:1 provided the most satisfactory result, with an average theoretical plate number of 5.2×103 plates/m. With an optimized temperature program, 11 PAH mixtures were completely separated within 27 min. The interactions between PAHs and these fascinating and interesting stationary phases are discussed.o characterize the binary stationary phase with BeMIM-TfO and Cu(S-C12)2, the thermodynamic parameters were obtained from a modified van’t Hoff plot. According to the isothermal retention data, which is transformed to enthalpy, entropy and Gibbs free energy losses as the probes (PAHs) partition between mesophases, similar solubilities of PAHs were observed in different mesophases. The other method was an Abraham model fitted by multiple linear regression analysis (MLRA). PAHs used as probes could describe the interaction tendency at various temperatures for the binary stationary phase and neat ionic liquid (IL) stationary phase. Both phases show that hydrogen bond acidity and dispersion force decrease and the π- and nonbonding interactions increase with increasing temperature.henols were chosen as analytes to obtain a deeper understanding of the retention mechanism of the binary stationary phase because they are more polar than PAHs and contain an oxygen atom. The influences of the operational variables flow rate and column temperature were studied. An optimal velocity of 17 cm/s with the best separation efficiency of about 9 × 103 plates/m was determined. The retention order was complicated due to participation in the retention mechanism of various interactions involved, such as hydrogen bonding, ligand exchange and shape selectivity. MLRA was used to determine the interaction change with various oven temperatures. Hydrogen bonding decreased and π-π interaction increased with increasing oven temperature. These results provide insight into the mechanism of the mixed mode interaction involved in the separation processes. simple and cost-effective solid-phase microextraction (SPME) device was developed. Fused silica capillaries were etched with ammonium hydrogen difluoride prior to coating with an ionic liquid. For comparison, both a bare fused silica capillary and one pretreated with a Nafion membrane were also coated with the ionic liquid. All of the coated capillaries were employed for the headspace microextraction of PAHs. The adsorbed analytes were separated with an established GC system. The optimization of the extraction process was also studied. The results indicated that the etched fiber displayed the most proficient extraction, not only giving highly reproducible extraction results but also having greater extraction efficiency. The Nafion membrane-supported fiber was inferior to the etched fiber, and untreated fused silica had the lowest efficiency. The Nafion membrane contains negatively charged sulfonate groups, and the increase in ionic liquid binding was due to electrostatic attractive forces. A more complicated adsorption and desorption mechanism, however, might provide less efficiency due to hydrophobic interactions with the polymer matrix in the Nafion membrane. The established method was also successfully applied for the analysis of a mosquito coil incense. A preliminary experiment was also preformed on SPME fibers coated with the phosphonium ILs.
Subjects
Ionic liquid
metallomesogen
complexation gas chromatography stationary phase
van’t Hoff plot
Abraham equation
solid phase microextraction
etching
phosphonium ionic liquid
polycyclic aromatic hydrocarbon
phenol
Type
thesis
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