| Extraction is a traditional technique for purifying matters. At present, the traditional extraction techniques for solid matrices include the well-known Soxhlet extraction, reflux and ultrasonication. Even though efficient extractions may be achieved using these simple techniques, the present major drawbacks, namely long extraction time, especially for soxhlet, high solvent consumption and low temperatures, and have yet to be readily automated. Therefore it is important to develop a fast and effective extraction method. The rapid heat transfer provided by microwave heating can result in a much shorter extraction time for analytics in complex samples in comparison with more traditional soxhlet or reflux extractions. Microwave energy is a non-ionizing radiation that causes molecular motion by migration of ions and rotation of dipoles. Dipole rotation refers to the alignment, due to the electric field, of molecules that have either permanent or induced dipole moments in both the solvent and samples. Microwave-assisted extraction (MAE) is suit to leach the instability compounds and the active constituents in Chinese herbal medicine. Comparing with supercritical fluid extraction, the apparatus of MAE is cheaper and the range of application is wide. The special features of microwave-assisted extraction technique over traditional extraction are short time, low temperature, low energy consumption and high product quality. Good experimental results of extraction Chinese herbal medicine by MAE show that it could be extensively applied in natural products. Three microwave-assisted extraction methods were studied. The first method is pressurized microwave-assisted extraction. In this system, the mode of WR-C special microwave sample preparation system with pressure and time control system was used and the extraction was carried in the pressurize PFA extraction jar. The second method is household microwave oven dynamic extraction. For this system, the microwave oven was modified. Two holes were drilled in the side of the oven in order to place the branch pipe of the extraction vessel. And the Extraction vessel was made up of glass, which couldn't absorb microwave energy. During the extraction, fresh solvent is continuously pumped through the extraction cell, which is maintained at a slight overpressure in order to keep the solvent in a liquid state; the third method is microwave resonant cavity dynamic extraction. In this study a novel microwave-assisted extraction device was presented. In this newly developed system, a 3/4 wavelength microwave resonance cavity was used as the microwave coupling device for replacing a traditional microwave oven. This field has not studied at present in China.MAE process of extracting flavonoids in Acanthopanax seticosus Harms, Radix Scutellariae and Flos Sophaoae were studied and the better yield was obtained. Other methods such as soxhlet extraction, dipping and ultrasound-assisted extraction were applied in the flavonoids extracted. And at the same time the results obtained by those methods were compared with each other. A new dynamic MAE method on flavonoids in Chinese herbal medicine was established. The yield of flavonoids was determined by spectrophotometer and the yield of baicalin, rutin and quercetin were determiner by high performance liquid chromatography (HPLC). The result demonstrated that comparing with the traditional soxhlet extraction MAE not only has taken a shorter time, but also simplifier the procedure, and made higher yield of the extraction. Comparing with the household microwave oven dynamic extraction system and microwave resonance cavity dynamic extraction system, pressurized microwave-assisted extraction system has the higher extraction yield. But comparing with pressurized microwave-assisted extraction system the extracts need filtrate and the other two methods can collect the extracts on-line. MAE process of extracting saponins and polysaccharide in Radix Astragali were studied. The yield of saponins and polysaccharide were determined by s...
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