Studies On Ultrasonic Nebulization Extraction Of Chemical Constituents From Plant Materials

Ultrasonic assistant extraction (UAE) has been widely applied to extraction of the analytes from many matrixes. It has been demonstrated that the UAE is expeditious, inexpensive and an efficient alternative to conventional extraction techniques. In the UAE process, the frequency of acoustic vibration is between 20-40 KHz. But, the investigation on the application of high frequency ultrasonic wave to extraction is scarce. In the ultrasonic nebulization extraction (UNE), the frequency of acoustic vibration is about 1.7MHz. Its extraction process was different from low frequency ultrasonic extraction. When the vibration was transmitted through the solvent,"ultrasonic fountain"and aerosol would occur at the same time. This phenomenon was named as"fountain nebulization". Based on the"ultrasonic fountain", aerosol and cavitation concentrating effect, the analytes was extracted from sample powder to extraction solvent. In this thesis UNE was applied to the extraction of various active constituents from plant materials.In the introduction the principles, characteristics and applications of UAE, UNE and liquid phase microextraction (LPME) were reviewed. And the common extraction methods for essential oil were introduced.The ultrasonic nebulization extraction (UNE) was applied to extract anthraquinones (emodin, aloe-emodin and rhein) from Rheum palmatum L. The extracts from Rheum palmatum L. was analyzed by micellar electrokinetic capillary chromatography (MECC) using sodium dodecyl sulfate (SDS). Several parameters of UNE, including type of extraction solvent, concentration of extraction solvent, volume of extraction solvent, extraction time and ultrasonic power, were examined and the optimized parameters were selected. Under the selected conditions, contents of emodin, aloe-emodin and rhein obtained from different cultivated areas of R. palmatum L. were 1.08-2.04 mg/g, 0.65-1.16 mg/g and 0.70-2.90 mg/g, respectively. The relative standard deviations (RSDs) for determining emodin, aloe-emodin and rhein were 1.3-2.4%, 1.9-4.7% and 1.3-3.9%, respectively. The recoveries for emodin, aloe-emodin and rhein were 91.67-101.54%,90.77-107.06% and 97.14-100.35%, respectively. Compared with maceration extraction (ME), reflux extraction (RE), stirring extraction (SE) and ultrasonic assistant extraction (UAE), the proposed method was more efficient, faster and easier to be operated and lower equipment costs and lower extraction temperature were required. The results indicated that UNE was a good alternative method for extracting anthraquinones from R.palmatum L.The ultrasonic nebulization extraction (UNE) was developed and applied to extract trans-anethole from fruits of Illicium verum Hook. f. and Foeniculum vulgare Mill. and limonene from Zanthoxylum bungeanum Maxim. The 100 mg of sample powders and 15mL of hexane were added in extraction vessel, the extraction was completed after 5 min for Illicium verum Hook. f. and Foeniculum vulgare Mill. and 30 min for Zanthoxylum bungeanum Maxim under 35W ultrasonic power. The trans-anethole and limonene were determined by gas chromatography. The extraction yields of trans-anethole in Illicium verum Hook. f., Foeniculum vulgare Mill. and limonene in Zanthoxylum bungeanum Maxim were 106.9-145.7 mg/g,23.4-30.1 mg/g and 0.55-1.55 mg/g, respectively. The recoveries were 90.95%-100.67% for trans-anethole and 90.0% -98.6% for limonene. Comparing with ultrasonic assistant extraction (UAE) and Soxhlet extraction (SE), the proposed method was more efficient, faster and easier to be operated. It has advantages of lower equipment cost, lower sound pollution and lower extraction temperature.A novel ultrasonic nebulization extraction (UNE) method coupled with on-line gas chromatography (GC) was proposed. In this method, six-way valve connects extraction vessel with GC sampling port and on-line UNE-GC method was developed. In the UNE the analyte was transferred and enriched from the solid sample to extraction solvent, and then to vapor phase in the headspace of extraction vessel. The sample gas containing analytes obtained by UNE was introduced into the sampling loop with the purging gas (N2). And then the sample gas in the sampling loop was introduced into the GC column. Several experimental parameters of on-line UNE-GC, including sampling time, flow rate of purging gas, standstill time and temperature of tubing, were optimized. The extraction yields of trans-anethole in Illicium verum Hook. f. and Foeniculum vulgare Mill. were 65.6-118.6 mg/g and 11.6-30.2 mg/g, respectively. The recoveries for determining trans-anethole were between 99.2% and 111.2% and RSDs are less than 8.3% when the UNE was applied. Compared with off-line system, the proposed on-line system is more suitable to detect volatile compounds. The extraction yields of trans-anethole obtained by on-line UNE-GC are much the same as those obtained by off-line UNE-GC. Compared with off-line system, the on-line UNE coupled with GC technique can minimal sample contamination and the possibility for a totally automated analytical system. There is a novel gas sampling method and it is suitable for the extraction of volatile compounds from spices. If the UNE coupled with many enrichment techniques (SPE, SPME, LPME and so on), the sensitivity of the proposed method would be improved.A method for analysis of essential oil in Cuminum cyminum L. and Zanthoxylum bungeanum Maxim using simultaneous ultrasonic nebulization extraction and headspace liquid phase microextraction (UNE-HS-LPME) followed by gas chromatography–mass spectrometry was developed. In the UNE process, the gas-liquid distribution equilibrium of analytes will be rapidly reached. And the volatile compounds will be enriched in headspace of extraction vessel. At this time, the organic phase was suspended in the headspace of extraction vessel, and analytes was enriched in organic phase. The mass transfer of the analytes from vapor phase to the suspended solvent continues. After enrichment, the suspended solvent microdrop was retracted back into the microsyringe and directly injected into the GC-MS system. Experimental parameters, including the kind of suspended solvent, microdrop volume, sample amount, extraction time, enrichment time, salt concentration and position of microdrop were examined and optimized. The 26 and 36 kinds of volatile compounds from Cuminum cyminum L. and Zanthoxylum bungeanum Maxim were identified by UNE-HS-LPME. Compared with hydrodistillation (HD), the extract obtained by UNE-HS-LPME is much the same as those obtained by HD. In addition, UNE-HS-LPME also provided higher enrichment effciency and sensitivity compared with stirring extraction (SE)-HS-LPME, ultrasonic assistant extraction (UAE) and UNE. The results indicated that the UNE-HS-LPME is simple and highly efficient extraction and enrichment technique.In this thesis, extraction principle and characteristic of UNE were studied and the method was used to extract active compounds from plants. Several experiment conditions were optimized. This experiment results indicated that the UNE method is a kind reliable extraction method of active compounds from plants. UNE coupled with on-line GC and LPME were used and detected volatile compounds from spices. The proposed methods extend the application of high frequency ultrasonic extraction.