Preparation Of Functional Room Temperature Ionic Liquids For The Separation Science

Nowday,more and more people focused on the sustainable development. The fashion of green chemistry is changing the face of the chemistry. Separation science plays a very important role in the field of analytical chemistry and chemical industry. However, many separation processes are harmful to environment because of the huge consume of volatile organic solvent. With the idea of green chemistry, we want to change this by applying ionic liquids as a novel green separation medium in separation science. Ionic liquid is a class of salt that has a melting point lower than 100℃. Owing to their nonvolatility and thermal stability, ionic liquids are known as greener alternative to traditional organic solvents. Moreover, ionic liquids are tunable. By designing their chemical structure, we can obtain"task special ionic liquids"to achieve target application. Based on the above-mentioned idea, we try to design and synthesize some functional ionic liquids for separation process.1 Preparation of high purity functional ionic liquidsAmino acid ionic liquids (AAILs) are a promising platform of task special ionic liquids. They are synthesized by ion-exchange methods. However, this method is not suitable for the synthesis of high quality ionic liquids. In chapter 2, we proposed an electrochemical method to prepare AAILs. Several AAILs with various alkylmethylimidazolium cations and amino acid anions were synthesized by using diaphragm electrolysis method. The end point of electrolysis was determined based on the conductance of the product. 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.For separation solvents, the quality requirement is critical. So, we are very interesting in the purity of ionic liquids. In fact, only a few analytical methods have been reported to control the quality of ionic liquids. In chapter 3, we developed a HPLC-ESI/MS method for AAILs quantificational analysis. Using heptafluorobutyric acid as ion pairing reagent, the retention of AAILs was improved. Under the optimized ESI/MS condition, LOD of this method is down to 1 ng/ml. This method was used to control AAILs quality.Alkylimidazolium ionic liquid is one of the most popular ionic liquids. However,many synthetic methodologies of ionic liquids lead to the final product with yellowish or brown color. Most commercially ionic liquids are still visibly colored. It can limit the application of ionic liquid in spectroscopy and separation. In chapter 4, with regard to the spectroscopic quality of ionic liquids, a solid phase extraction apparatus with octadecylsilyl (ODS) solid phase was proposed to separate these impurities from ionic liquids via hydrophobic interaction. The change of the colored impurities during the purification process was monitored by HPLC and UV-Vis spectrometry. In comparison with other existing purification methods, our method is advantageous to solve the purification problem of ionic liquids, especially suitable for some ionic liquids containing strongly hydrogen-bonding anions.2 Application of task special ionic liquids in separationAdrenergic amines, such as octopamine, synephrine and tyramine, can strongly interact with the free silanols on the surface of stationary phase. That directly causes the band tailing of analytes and affects the separation and the quantitative analysis. In chapter 5, ionic liquid was used as a mobile phase additive for improving the separation of adrenergic amines. The addition of ionic liquid resulted in decreasing band tailing, increasing retention and improving resolution.The contents of octopamine, synephrine and tyramine in Citrus herbs were accurately determined by this'green'chromatographic method.In chapter 6, to develop environmentally friendly chromatographic methods, aqueous solutions of low toxicity ionic liquids were proposed as environmentally friendly mobile phases for the HPLC analysis of nicotine and cotinine. The influencing factors on the retention behaviors of analytes were studied in detail. The analysis of serum samples was achieved.AAILs are a class of chiral ionic liquids and have the potentials for application in chiral separation. In chapter 7, we present the first application of AAILs in chiral separation of four pairs of underivatized amino acid enantiomers. The L-proline ILs coupled with Cu²⁺ was used as chiral selectors because L-proline has been proved to be an outstanding ligand in organocatalysis and organometallic catalysis. Chiral recognition is achieved based on the formation of ternary mixed metal complexes between the AAIL ligand and the analyte ligand. The different complex stability constants of the mixed complexes with D- and L-enantiomers result in the enantioseparation of racemic amino acids. The method was validated with two major chiral separation techniques, HPLC and CE. In both techniques, AAILs show a significant superiority over the conventionally used amino acid ligands. In chapter 8, we demonstrate a novel application of functional AAILs in enantioselective liquid-liquid extraction. Using these functional ionic liquids as acceptor phase and ethylacetate as donor phase, L-enantiomer of amino acid was enriched in the ionic liquid phase, while D-enantiomer of amino acid was predominated into the donor phase. In the extraction process, these AAILs performed two roles in the liquid-liquid extraction approach. As solvent, they act as an efficient and stable acceptor phase for amino acids. As selector, AAILs coupled with Cu2+ exhibit distinct enantioselectivity in the separation of racemic amino acids. According to the study of the influencing factors, we found that the amino acid enantiomers are separated based on the chiral ligand-exchange mechanism. Noteworthly, we found that the AAILs can achieve enantioselective extraction at very high amino acids concentration (112-155 mM). It was much higher than the reported works for the chiral extraction of amino acids (1-20 mM). As chiral separation media, the high separation capacities of ionic liquids have obvious advantages for chiral extraction in preparative scale.3. Sample preparation for analyzing traditional Chinese medicinesBased on our group's research, we reviewed the recent progress of the sample preparation for analyzing traditional Chinese medicines in chapter 9. We focused on the new sample preparation methods, which make the whole analysis to be more selective, more sensitive and more environmentally friendly. In addition, new materials, new devices and new procedures involved in the sample preparation of TCM were discussed.