Studies On Ultrasonic Nebulization Extraction In Volatile Organic Compounds Pretreatment

The ultrasonic vibration energy in the ultrasonic nebulization extraction (UNE) iscoupled the sample solution by the coupling water. Due to the high frequency of the acousticvibration, the cavitation effect, the “ultrasonic fountain” and the aerosol are introduced in thesample extraction process, thus a better extraction efficiency of volatile organic compounds incomplex matrix was obtained.Ultrasonic nebulization extraction, liquid phase microextraction, extraction column,activated carbon, solid phase extraction and purging technology were combined in the paper.Two new devices in sample pretreatment for volatile organic compounds were developed. Thedevices were applied to practical sample analysis.In the introduction, the ultrasonic nebulization extraction, liquid phase microextraction,solid phase extraction and purging technology were described, including principle,characteristics and applications. Introduce of essential oil, including the composition,application and extraction methods. And a variety of sample pretreatment technology wasintroduced systematically, including principle, characteristics, the scope of application and theapplication status. From the statement of the previous introduction, the background, the statusand the investigate method of the paper is established.In chapter2, the extraction and enrichment device combining ultrasonic nebulizationextraction and liquid phase microextraction was proposed. The extraction solvent (organicsolvent) placed on the bottom of the self-made extraction column, the target compounds weretransferred from the gas phase in extraction vessel to the extraction solvent in the extractioncolumn through the purging gas. The condensation system was wounded out of the extractioncolumn. It was advantageous to decrease the volatility of target analyte accompany with thepurging gas. After the extraction process, the extraction column was put upright, the upper organic layer containing the analytes were separated from the under water layer, effectiveextraction and enrichment were obtained. The ultrasonic nebulization extraction–extractioncolumn-liquid phase microextraction (UNE–EC–LPME) was developed for the extraction ofvolatile organic compounds in Foeniculum Vulgare Mill. The main factors affecting extractionefficiency were studied and optimized. The shape of column, the extraction temperature, thetype of extraction solvent, the volume of extraction solvent, the flow rate of purging gas, thepurging time and standing time were evaluated. Compared with the dynamic and staticultrasonic nebulization extraction–single drop microextraction (UNE–SDME), the proposedmethod has higher extraction efficiency.21and21kinds of different volatile compounds wereidentified by UNE–EC–LPME and hydrodistillation (HD, standard method recommended byChinese Pharmacopoeia), respectively. The RSD values for the main ingredients are all lessthan5.0%. The proposed method solved the problem that the microdrop seemed to beunstable or tend to drop down in the process of single drop microextraction. The deviceprovides a simple, fast method with high extraction and enrichment efficiency for thedetermination of the volatile organic compounds.In chapter3, a new extraction device, ultrasonic nebulization extraction coupled withactivated carbon solid phase extraction was developed and applied to extract and enrich thevolatile organic compounds. Several experimental parameters affecting the extraction resultwere studied and selected. The sample was extracted by0.4g activated carbon, the flow rateof200mL/min, after5min the target analytes were eluted by50μL of n-teradecane. Under theoptimum conditions, the enrichment factor of β-myrcene, limonene, estragole andtrans-anethole were56.24,14.09,86.72and81.23, respectively. The contents of compoundsobtained by ultrasonic nebulization extraction-activated carbon-solid phase extraction(UNE–AC–SPE) and HD are similar,20and21kinds of different volatile compounds wereidentified by the two methods. The RSDs for several kinds of main ingredients are1.8%-5.6%,so the repeatability is good. The proposed method overcomes some shortcomings ofhydrodistillation, such as, large expenditure of sample and reagents, long extraction time andlarge energy consumption. The proposed pretreatment method is a simple, fast and effectiveanalytical technology. UNE–AC–SPE was a feasible method for extraction and enrichment ofthe volatile compounds in spices.