Studies On Ultrasonic Nebulization Single Drop Microextraction Of Volatile Arid Semivolatile Constituents In Natural Products

The ultrasonic nebulization can be applied to the preparation of samples. Thefrequency of acoustic vibration in the UN is about1.7MHz. Owing to the acousticvibration with high frequency, liquid medium was stretched, torn and sprayed, whichresults in “ultrasonic fountain” and aerosol would occur at the same time. Thegeneration process of dispersible or tiny droplets in the gas phase is called ultrasonicnebulization. Extraction of the analyte in the sample by ultrasonic nebulization iscalled ultrasonic nebulization extraction (UNE). Extraction efficiency of volatile andsemivolatile constituents in natural products was related to the “ultrasonic fountain”,aerosol and cavitation effect. Headspace single drop microextraction (HS-SDME) isan environment friendly sample pretreatment method, and has the advantages, suchas simplicity, rapidity, low cost, low pollution and high enrichment factor. It may besuitable for the extraction of the volatile constituents and the semivolativeconstituents in natural products. UNE, HS-SDME, purging and heating methodswere combined in this thesis. The ultrasonic nebulization-heating gas flow transfer-single drop microextraction (UN-HGFT-SDME) and ultrasonic nebulization-headspace ionic liquid single drop microextraction (UN-HS-IL-SDME) weredeveloped and applied to the extraction of various active constituents in naturalproducts.In the introduction, UAE, UNE, SDME and purging method were reviewed,including principle, characteristics and applications of these methods. And characteristics, types and applications of ionic liquids in SDME were introduced.UN-HGFT-SDME was developed for the extraction of the semivolatile andvolatile constituents from Zanthoxylum bungeanum Maxim. In the UN-HS-SDME,the target analytes were transferred from the solid phase (sample powders) to theliquid phase (extraction solvent) and then to the headspace aerosol. The aerosol wastransferred to the gas phase by ultrasonic fountain and then dropped into the bottomof the vessel by gravity time by time. The analytes were transferred to the gas phasein the process. The distribution equilibrium of analytes in the gas phase and theaqueous phase was reached rapidly. The concentration of the semivolatileconstituents in the gas phase should be low at low temperature. However, theintroduction of heated carrier gas can result in the increase of the temperature of thesystem and the increase of concentration of semivolatile constituents in the gas phasein UNE. The semivolatile and volatile constituents were transferred rapidly from thegas phase to the organic phase (suspended solvent) by the purging. The hightemperature is beneficial to the increase of concentration of semivolatile constituentsin the gas phase and the loss of cooling constituents was reduced. The concentrationof the volatile constituents and semivolatile constituents in the suspended solventincreased. Thus the extraction of analytes was more effective. Experimentalparameters, including the kind of suspended solvent, microdrop volume, extractiontime, temperature of heating gas and flow rate of heating gas were examined andoptimized.The constituents of the pericarp of Zanthoxylum bungeanum Maxim. wereextracted by HD, UNE-SDME and the present method and then analyzed by GC–MS.The kinds of the compounds obtained by HD and the present method are much thesame. The total content of determined compounds obtained by HD andUN-HGFT-HS-SDME are99.29%and99.52%, respectively. The relative contents ofthe major constituents obtained by the present method are similar to these obtainedby HD, but much different from these obtained by UN-HS-SDME. The resultsindicated that the present method is more suitable for the extraction of the volatileand semivolatile constituents from the natural products. The RSDs for determining4-methyl-1-(1-methylethyl)-bicyclo[3.1.0]hexene,(E)-3,7-dimethyl-1,3,6-octatriene,linalool,3,7-dimethyl-2,6-octadien-1-ol,3-methyl-6-(1-methylethyl)-2-cyclohexen-1 -one and terpinyl acetate are1.5%,3.6%,5.0%,4.4%,6.7%,6.1%respectively. Tovalidate the feasibility of the present method, the other two different kinds ofZanthoxylum bungeanum Maxim. from different cultivated areas were also studied inthis study. The relative contents of constituents in Zanthoxylum bungeanum Maxim.obtained by UN-HGFT-SDME and HD are similar to each other. The resultsindicated that the UN-HGFT-SDME is suitable to extract the semivolatile andvolatile constituents from the natural products.UN-HS-SDME using ionic liquid (UN-HS-IL-SDME) was developed. Ionicliquid has the characteristics of a less volatile, good thermal stability and isenvironmentally friendly.The drawback of traditional organic solvents of operating athigh temperature is overcome when IL was used. The experimental conditions werestudied and optimized. The volatile and semivolatile constituents in Myristicafragrans Houtt. were extracted under the selected conditions.32and33kinds ofvolatile and semivolatile constituents were obtained by UN-HS-IL-SDME and HD.The relative contents of volatile constituents obtained by UN-HS-IL-SDME werelower than these obtained by HD, but the relative contents of semivolatileconstituents were higher than these obtained by HD. Compared with UA-HS-SDMEand SE-HS-SDME, the present method was more efficient and faster and less solventis required. The results indicated that UN-HS-IL-SDME was a feasible method forextracting the volatile and semivolatile constituents in Myristica fragrans Houtt.Volatile and semivolatile constituents in citrus peel were extracted byUN-HS-IL-SDME. Several experimental parameters affecting extraction efficiencywere optimized and are as follows: the suspended solvent,[C6MIM][BF4]; solventmicrodrop volume,17.5μL; microdrop position,1.5cm; extraction time,5min; thetemperature of extraction vessel,60℃and enrichment time,15min. The analytesobtained were injected into GC-MS system for analysis.23and12kinds of volatileand semivolatile constituents were obtained by UN-HS-IL-SDME and HD.Compared with HD, UN-HS-IL-SDME is more suitable to the extraction ofsemivolatile constituents. The kinds of the compounds obtained by HD mainly arevolatile constituents, and these obtained by UN-HS-IL-SDME are volatile andsemivolatile constituents. The reason may be that semivolatile constituents in citrus peel could pass easily through the cell membrane and in ultrasonic nebulization. Theanalytes in the extract then were transferred to the headspace phase, transferred togas phase by heating and extracted by ionic liquid. Therefore, UN-HS-IL-SDME isfeasible to extract the volatile and semivolatile constituents in natural products andhas the high extraction efficiency and enrichment factor for analytes.HS-SDME can only extract analytes in the gas phase, and in the liquid phaseextraction, analytes commonly were extracted in the liquid phase. When HS-SDMEwas applied, the analytes must be transferred from the sample (solid phase) to theliquid phase and then to the gas phase or directly transferred from sample (solidphase) to gas phase by the other method. When UNE was applied, the analytes weretransferred from the sample (solid phase) to the liquid phase and then to the gasphase at the same time. This is a unique advantage of UNE.