Synthesis Of Functional Ionic Liquids And Their Applications In High-performance Liquid Chromatography

Room-temperature ionic liquids (RTILs) are a group of organic salts whose melting points range from ?81°C to 125°C. They have unique chemical and physical properties, such as good stability, non-volatility, tunable miscibility with water, ease to be functionalized and so on. Thus, they have been appropriately regarded as"green solvents"or"designable solvents". Ionic liquids have been used as green alternatives to volatile organic solvents in various analytical applications including chromatography, mass spectrometry, spectroscopy, and electrochemistry. In order to prepare functionalized ionic liquids of high-purity and to broaden their application in chromatography, we have carried out the following novel works:1. In this work, several amino acid ionic liquids (AAILs) containing different alkylmethylimidazolium cations and amino acid anions were synthesized using diaphragm electrolysis method. The end point of electrolysis was determined by monitoring the conductance of the product and calculated by Faraday's Law. The as-prepared AAILs were characterized by nuclear magnetic resonance (NMR) and high performance liquid chromatography-electrospray ionization/mass spectrum (HPLC-ESI/MS). Compared with ion-exchange method, AAILs synthesized by diaphragm electrolysis method had higher yield and purity. Therefore, diaphragm electrolysis has great potentials in the preparation of high-purity AAILs.2. We present the first application of AAILs in chiral separation based on chiral ligand-exchange principle. By using 1-alkyl-3-methylimidazolium L-proline as chiral ligand coordinated with copper(II), four pairs of underivatized amino acid enantiomers (DL-Phe, DL-His, DL-Trp, and DL-Tyr) were successfully separated in two major chiral separation techniques, HPLC and CE, with higher enantioselectivity than conventionally used amino acid ligands (Rs 3.26-10.81 for HPLC and 1.34-4.27 for CE). Interestingly, increasing the alkyl chain length of AAIL cation remarkably enhanced the enantioselectivity. It is inferred that the alkylmethylimidazolium cations and L-Pro form ion-pairs on the surface of stationary phase or on the capillary inner surface. The ternary copper complexes with L-Pro are consequently attached to the support surface, inducing an ion-exchange type of retention for the DL-enantiomers. Therefore, the AAIL cation plays an essential role in the separation. This work demonstrates that AAILs are good alternatives to conventional amino acid ligands for ligand-exchange-based chiral separation. It also reveals the tremendous application potential of this new type of task-specific ILs.3. We demonstrate a novel extracting system based on the use of IL surfactants in ultrasonic-assisted extraction (UAE) followed by high-performance liquid chromatographic (HPLC) analysis. No organic solvents were used in the extraction, making this method environmentally friendly and more attractive than the conventional organic solvent-based extraction methods. As an example, the method was applied successfully to the determination of tanshinones in Chinese herbal medicine Salvia miltiorrhiza bunge. The effects of the carbon chain length of the IL cation and the influencing factors in UAE were investigated in detail. Under the optimized conditions, satisfactory extraction efficiency was achieved with the recoveries range from 87.5 % to 107.6 %, and relative standard deviations (RSDs) lower than 6 %.