The Separation And Analysis Of Trace Components In Complex Samples

The separation and analysis of trace components in complex samples is one of the most popular research fields in analytical chemistry at present, for example, the separation and analysis of various contaminations in soil, the separation and analysis of various effective components in Chinese traditional medicine and the separation and analysis of various components in tobacco. The pesticide is one of the most important contaminations in soil. The analysis of pesticide residues in soil has attracted much attention. One of the most popular research fields is to develop some new extraction and detection methods. How to simplify the process of separation and analysis of the chemical components in Chinese traditional medicine and to solve the problem that it is difficult to identify multiple components simultaneously is the significant task in Chinese traditional medicine research. During the production and storage of tobacco, many conventional flavors have the problem of easy volatilization. The application, of flavor precursor is a good method to solve the above-mentioned problem.First of all, a novel method, modified matrix solid-phase dispersion (MMSPD), has been developed for quantitative analysis of pesticide residues in soil. The method has good extraction efficiency and cleanup efficiency and it is not necessary to further separate the pesticide residues from interfering substances by cleanup steps before chromatographic analysis of extract. The method also had good repeatibility and low detection limits. Under the comparable conditions, the extraction efficiency of MMSPD is superior to that of the traditional method. Secondly, volatile oil of Rhizoma polygonati is obtained by simultaneous distillation-solvent extraction. Following, the essential oil is analyzed by gas chromatography and gas chromatography-mass spectrometry. Thirdly, two glucosidic bound flavor precursors are synthesized and their structures are characterized by IR, ~1H NMR and ESI-MS. Their thermal decomposition process is investigated by thermogravimetric analysis and differential thermal analysis and their prolysis products are investigated by on-line pyrolysis gas chromatography-mass spectroscopy.There are six chapters in the dissertation and the content of each one is as following:Chapter 1 provides a critical review of existing methods for analyzing pesticides in soil. The state-of-the-art techniques for sample preparation, analyte separation and detection are described.Chapter 2, at first, a novel method, modified matrix solid-phase dispersion (MMSPD), has been developed for quantitative analysis of organophosphorus pesticide residues in soil. It is based on matrix solid-phase dispersion (MSPD) and continuous liquid-solid extraction (continuous LSE), using Florisil as sorbent and dichloromethane as the recycling solvent. Two soils with different texture and physicochemical properties are studied to validate the method. The effect of residence time of pesticides in soil on the recoveries is also studied. MMSPD is compared with MSPD and continuous LSE respectively. In' the same conditions, the MMSPD extraction efficiency was much better than that of MSPD or that of continuous LSE. Determination is carried out by gas chromatography with nitrogen-phosphorus detection. Two pesticide residues have been detected in real soil samples from Fujian, China, using MMSPD. The pesticides were confirmed by gas chromatography-mass spectrometry in a selected-ion monitoring mode. Secondly, a rapid analytical multiresidue method is developed for the quantitative analysis of various classes of pesticides in soil, based on the MMSPD, using Florisil as the dispersant and acetone as the extracting solvent. Determination was accomplished by gas chromatography with nitrogen-phosphorus detection. The effect of residence time of pesticides in soil was studied in order to evaluate if the adsorption on the soil colloids had some influence on the pesticide recoveries. The pesticides included in this work belonged to three pesticide groups: carbamate insecticide (pirimicarb), bactericide (metalaxyl), herbicide (metolachlor, isopropalin and pendimethalin). The method gave recoveries ranging from 93% to 100% with relative standard deviations (RSDs) lower than 10%. The limits of detection (LODs) ranged from 0.2 to 2.0 ng/g. Chapter 3 provides a review of volatile aroma compounds and flavor precursors in plants or other samples. The techniques for sample preparation, analyte separation and detection are mainly described. The flavor precursor that can release aroma compounds by degradation is also introduced.Chapter 4, volatile oil of Rhizoma polygonati is obtained by simultaneous distillation-solvent extraction. Following, the essential oil is analyzed by gas chromatography and gas chromatography-mass spectrometry. Forty-two components were identified, constituting approximately 96% of the oil.Chapter 5, two glucosidic bound flavor precursors, benzyl 2, 3, 4, 6 - tetra - O -acetyl -β- D - glucopyranoside and phenyl ethyl 2,3,4, 6 - tetra - O - acetyl -β- D -glucopyranoside are synthesized respectively by Koenigs-Knorr method. Their structures are characterized by IR, ~1H NMR and ESI-MS.Chapter 6, the thermal decomposition process of two synthetic glucosidic bound flavor precursors is investigated by thermogravimetric analysis and differential thermal analysis. The total degradation of them is from 200 to 300℃. The weight loss rate is largest appeared at Tp of about 250℃, which is associated with the endothermic peak showed in DTA curve. The prolysis products of two synthetic glucosidic bound flavor precursors are investigated by on-line pyrolysis gas chromatography-mass spectroscopy. The mechanism of the pyrolysis is described. The results indicate that there is a significant amount of benzyl acohol and phenylethyl alcohol occurred and fewer by-products at 250℃.