| The presence of pesticide residues in foodstuff such as Chinese tea is an escalating problem that has aroused public concern over potential health hazards. Analytical techniques such as gas chromatography (GC), high performance liquid chromatography (HPLC), and GC mass spectrometry (MS) allow for the accurate determination of pesticide residues in tea samples. However, they require sophisticated procedure for sample preparation before analyzing so as to remove or eliminate the effects from matrices. Ordinary methods for sample preparation, such as soxhlet extraction (SOX) and liquid-liquid extraction (LLE), often are time- and solvent-consumed. Ultrasonic extraction (USE), solid phase extraction (SPE), supercritical fluid extraction (SFE), and microwave-assisted extraction (MAE) have been found more and more applications in analysis of pesticides residues. In this work, we concentrated ourselves on development of simple, rapid and accurate methods for analysis of pesticides residues in Chinese tea by novel GC and HPLC techniques.This dissertation consists of three parts. The first chapter summarized the progress of pesticides residues analysis in foodstuff. The second part is the main body of the thesis including Chapter 2, 3, 4, and 5, in which a procedure for rapid analysis of BHC, DDT, dicofol and pyrethroids in tea by GC was proposed. A method for determination of cypermethrin and fenvalerate in tea by HPLC was also proposed in this part. Preliminary studies for sample preparation with ultrasonic extraction and determination of organophosphatesby GC with nitrogen phosphorus detector (NPD) were also described in this part. The third part is application of developed methods in the analysis of real world tea sample.The first chapter mainly introduces some commonly used sample preparation methods and their applications in the analysis of pesticide residues. These methods include ultrasonic extraction (USE), solid phase extraction (SPE), supercritical fluid extraction (SFE), solid phase micro-extraction (SPME), microwave aided extraction (MAE), gel permeation chromatography (GPC), matrix solid phase dispersion (MSPD) and accelerated solvent extraction (ASE).In the second chapter, an optimized procedure was proposed to rapidly analyze the residues of BHC, DDT, dicofol and pyrethroids in Chinese tea by GC with electron capture detector (BCD). The pesticide residues were extracted with a mixture of H-hexane and acetone (97.5:2.5, v/v) on a novel shaker at 40-42癈. The analytes were purified by a column (70mm x 5mm) packed with about 320 mg florisil and top packed with 28mg active carbon. Petroleum ether mixed with acetic ether (9:1, v/v) was selected to elute the residues from column. After extraction and purification, analyses of BHC, DDT, dicofol and pyrethroids were carried out by capillary gas chromatography with GC-ECD. Recoveries of all pesticides in spiked sample ranged 72.3~100.0%.In the third chapter, a method for analysis of cypermethrin and fenvalerate in Chinese tea by HPLC with diode array detector (DAD) was proposed. Thesteps for pesticide residues extraction and purification are similar with that in Chapter 2. The mobile phase is a mixture of acetonitrile and water (76:24, v/v) at flow rate of 1.2 mL-min. Maximum absorbance was found at 198 nm for both pesticides. Recoveries for cypermethrin and fenvalerate in spiked sample are 71% and 76%.The fourth chapter reported preliminary study of the application of USE in analysis of BHC, DDT, dicofol and pyrethroids in Chinese tea by GC-ECD. Experiment results show that USE can extract the analyte targets with efficiencies of around 100% compared with that of novel shaker used in Chapter 2. The results also show that extraction efficiency varies for different pesticide residues. Preliminary investigation indicated USE is an alternative for pesticide analysis in Chinese tea with GC-ECD.Chapter 5 starts a new investigation for rapid analysis of organophosphates in Chinese tea by GC-NPD. Acetone was selected as extraction solvent. Anal... |
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