離子液體輔助金屬液晶塗佈於氣相層析管柱及應用於固相微萃取技術

本研究選用螺旋柱狀的含銅金屬液晶(Cu(S-C12)2)作為氣相層析靜相應用於分離多環芳香碳氫化合物(PAH)。利用離子液體(BeMIM-TfO)的高黏滯性輔助Cu(S-C12)2動態塗佈於毛細管管柱，藉此克服金屬液晶分子不易固定於管柱表面之缺點。在微差掃描熱卡計及熱重分析儀中發現Cu(S-C12)2與BeMIM-TfO混合後兩者相轉移溫度及熱穩定溫度皆有改變。並於紫外可見光吸收光譜中發現Cu(S-C12)2中二價銅離子錯合物的d-d躍遷在與BeMIM-TfO混合後紅位移約10 nm，因此推測兩者之間有作用力存在。測試不同比例的靜相組成BeMIM-TfO及Cu(S-C12)2 (1:0, 1:1, 1:2 及1:3 (w/w))分離PAH。將Cu(S-C12)2比例提高可使PAH基線分離，並於比例1:1有最佳分離效率，平均理論版數達5200 plates/m。梯度升溫條件下，可將11種PAH於27分鐘內完全分離。進而利用van’t Hoff繪圖之斜率與截距所得之PAH分佈於不同靜相態中的ΔS，ΔH及ΔG比較其層析行為。由自由能在兩相間差異趨近於零推知PAH在兩相具有相似的溶解度。以多重線性回歸將Abraham所提出的五種分子間作用力應用於分析該靜相對多環芳香碳氫化合物的作用力。結果發現氫鍵及分散力隨著管柱溫度增加而下降，π鍵則上升。進一步在酚類化合物的分析中發現分離機制更為複雜，氫鍵、配位基交換及形狀選擇性都存在於此複合式靜相的分離機制中。本研究開創出簡便且經濟之固相微萃取裝置以熔融矽毛細管做為萃取纖維。將毛細管表面以二氟氫化胺飽和溶液蝕刻後塗佈上離子液體(BMIM-PF6)並以頂空萃取方式偵測PAH分析物。在光學顯微鏡下發現蝕刻後的粗糙表面將有助於離子液體的塗佈量的提升。最佳蝕刻條件為毛細管纖維浸入蝕刻溶液30分鐘後於250 ºC下加熱1小時。比較陽離子交換膜(Nafion)修飾及未修飾之萃取纖維塗佈BMIM-PF6後萃取PAH情形。其結果顯示蝕刻效果最佳，Nafion修飾次之，未修飾之管柱為末。蝕刻修飾比未修飾之纖維在相同萃取條件下層析面積提高了五倍之多。Nafion膜具有陰離子磺酸基可藉由靜電作用力增加離子液體塗佈量，但是其複雜分配機制造成較差的萃取效率。此系統並應用於真實樣品-蚊香燃燒煙之複雜機質中PAHs的偵測。本研究並以tetraalkylphosphonium陽離子之離子液體塗佈於萃取纖維上。發現使用此類離子液體塗佈之纖維具有不易脫落之優勢，並可用於連續多次取樣而不需重複塗佈。並且由光學顯微鏡下發現不需Nafion膜輔助即可形成均勻化的塗佈，在固相微萃取技術塗佈離子液體的應用上具有其前瞻性。

關鍵字

離子液體；金屬液晶；氣相層析靜相； van’t Hoff 方程式；多重線性迴歸；固相微萃取；毛細管表面修飾；多環芳香碳氫化合物；酚類化合物

並列摘要

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. To 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. Phenols 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. A 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.

並列關鍵字

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

參考文獻

Chapter 1

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離子液體輔助金屬液晶塗佈於氣相層析管柱及應用於固相微萃取技術

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