Novel Technology For Ultrasound-assisted Extraction And Its Study On Application In Analytical Chemistry

Based on the review of the principle and methodology of ultrasound-assisted extraction technique, and of advance in extraction and determination method of polyphenols in tobacco and tea, a series of practical, fast, effective extraction and analysis methods had been built up. This dissertation was made up two parts. 1) One was the study on the extraction and clean-up of polyphenols in tobacco. In this part, two new ideas, namely dynamic ultrasound-assisted extraction (DUAE) and simultaneous filtration and cleanup, were proposed and, the corresponding devices were designed, the principles and mechanisms of those processes were investigated, and finally the method constructed were successfully applied to the extraction and clean-up of polyphenols in tobacco. 2) The other was the analysis of catechins and caffeine in tea. DUAE method was improved and optimized, and then introduced to the extraction of catechins and caffeine in green tea samples, which not only broadened the application ranges of DUAE but also enhanced the extraction effectiveness of the analytes in teas, compared to other method such as ultrasound-assisted extraction. Systematic HPLC-DAD method in analysis of catechins and caffeine in black tea samples was established. The main results of the studies were as follows:1. A novel extraction method, namely DUAE, was constructed, in which the dynamic mode and the ultrasound-assisted technique was employed. The transfer mechanism of the analytes and the corresponding influence factor were investigated in the extraction. The main advantages of the method were to reduce both time and solvent consumption, decrease possibility of decomposition and oxidation of the analytes due to application of ultrasonic energy in dynamic mode during extraction, and thus very suitable for fast extraction of the property-labile compounds. The solvent and time-consumption during DUAE, as well as the recovery and reproducibility in analysis, were investigated in the study. It was found that the analytical method, based on DUAE technique, was more time- and solvent-saving, efficient, and fast than that of static UAE technique in analysis of tobacco polyphenols.2. A novel art-work combined filtration and clean-up device was designed, and used for simultaneous filtration and clean-up (SFC) of six polyphenols in tobacco. The suitable extraction solvent and clean-up material were selected, and the principle of SFC was described. Optimized HPLC-DAD analytical method, with multi-wavelength detection, was built up and used for simultaneous determination of the polyphenols in tobacco. The investigation provided not only theoretical and practical method for SFC of polyphenos in tobacco, but also HPLC separation and determination technique for the components.3. Based on the investigation of physico-chemical characteristics of catechins and caffeine, and influence of matrix in green tea, an improved DUAE method was constructed for extraction of five catechins and caffeine in tea sample. The tea extract could be directly analyzed by HPLC-DAD, owing to the filtration function of extraction column in DUAE system, not only improving the extraction efficiency, but also simplifying analytical step. Application of the method to a variety of the commercial Chinese tea samples, involving green and black teas, the linear range, selectivity, accuracy, precision and robustness were shown acceptable values, whereas the extraction efficiency and rate were greater than that of the chemical extraction method. It was further confirmed that DUAE could be widely applied to the extraction of the property-labile components in plant sample based on this study.4. A sensitive and fast method for determination of catechins and caffeine was constructed. The best absorption wavelength for five catechins (EGCG, EGC, ECG, EC, +C) and caffeine was found at 205 nm, and limits of determination (LOD) were obtained in the range of 0.01-0.04μg·mL^-1 at the wavelength. The optimized HPLC method was constructed, using RP C₁₈ column (150×4.6 mm, ID; 5 μm) with acetonitrile and 0.03% of trifluoroacetic acid as mobile phase at gradient elution (flow rate: 1 mL·min^-1 ), for analysis of five catechins and caffeine. Chromatographic run time was 15 min, and no interference peak was appeared in the condition. Recoveries for the analytes were in the range of 92-110%, and RSDs were less than 2.7%. The method was very suitable for sensitive and fast determination of catechins and caffeine in low-content tea samples (such as black tea).