| Tea is a popular beverage consumed worldwide and valued for its specific aroma and favour as well as potential health promoting properties. China is one of the largest tea producing and exporting countries in the whole world. Various pesticides, such as organochlorine pesticides (OCPs), organophosphorus pesticides (OPPs), and pyrethroids, are commonly used in tea planting for pest and disease control. These pesticides have been shown potential harmful effects to the environment and human being. In order to protect the health of consumers and regulate the international tea trade, several countries and international organizations have issued more and more strict maximum residue limits (MRLs) of pesticides for tea. Taking into account these facts, rapid, cost-effective, sensitivity, and accurate multi-pesticides residue analysis represents an important task for both the tea exporters and importing countries. Therefore, the establishment of methods for residue analysis of multi-pesticides in tea is of practical importance.In this thesis, multiple analysis methods for different testing requirements were studied systematically and developed for the analysis of pesticide residues in tea. An effort has been made to monitor of32pesticide residues (organophosphorous, organochlorine and pyrethroids) in223tea samples collected from different tea districts of China during the period of July2010to May2012. And a risk assessment was conducted in order to determine the degree of risk according to pesticide residues detected in tea samples. In addition, methods were applied successfully in an international comparison project to determine of mid-polarity pesticides in tea. Finally, a reference material for incurred residues of11pesticides in tea sample has been producted. The main research results were as follows:1.The analysis methods of9pesticides (OCP and pyrethroids) in tea sample, which were suitable for the rapid detection and high accuracy determination, were developed respectively. The effieient method with soxhlet extraction and accelerated solvent extraction, clean-up with gel permeation chromatograph and solid phase extraction (SPE) technique for the determination of9pestieide residues in tea by gas chromatography-masss spectrometry (GC-MS) has been established respectively. The results indicated that soxhlet extraction was adopted on accurate determination of pesticide residues in tea samples, and accelerated solvent extraction (ASE) was applicable for establishing the high precision detection method for pesticide residues in tea samples due to time saving and high efficiency. The method with shaking extraction and ultrasonic extraction, clean-up only with SPE technique for the determination of9pestieide residues in tea by gas chromatography-masss spectrometry (GC-MS) has been also established respectively. Shaking extraction, which is convenient and timesaving. can be used as rapid detection technique for simple, and meet the requirements of routine analysis. Ultrasonic extraction was not used finally in the paper with the worst reproducibility owing to the distribution of the ultrasonic field is not uniform in the ultrasonic device. The established shaking method which is suitable for rapid detection was applied successfully to18real tea samples for the detection of9pesticides. The result indicated that it was reliable and capable for daily analysis of9pesticides in tea.2. The rapid detection method for determination of the32pesticides (organophosphorus, organochlorine and pyrethroids) in tea samples was established. The validation method provided good linearity as the correlation coefficients higher than0.99for all analytes. The respective LODs (S/N=3) were0.34ng·g-1-18.88ng·g-1, and LOQs (S/N=10) were1.14ng·g-1-61.59ng·g-1, which were below the EU MRLs. The method is effective, quick, sensitive and reprodueible. It’s meet the requirements for daily trace analysis. An effort has been made to monitor the residue levels of32pesticides (organophosphorus, organochlorine and pyrethroids) in tea samples collected from different tea districts of China for three years using the established method. And the rules of pesticide residues in tea have been clear. A risk assessment was conducted in order to determine the degree of risk according to pesticide residues detected in tea samples. The result showed that it could not be considered a serious public health problem at present, although a lot of pesticide residues in tea samples were found. Nevertheless, an investigation into continuous monitoring and tighter regulation of pesticide residues in tea samples is recommended or even necessary for public health protection.3. A headspace solid-phase microextraction gas chromatography-isotope dilution mass spectrometry (HS-SPME/GC-IDMS) method for the simultaneous quantification of8pesticides in tea samples has been developed. By using isotopic dilution technique, the relative standard deviation (RSD) for8analytes was improved to3.7-10.2%, compared with the RSD of6.5-26.7%with traditional external standard method. The limits of detection (LODs) ranged from1.2to22.1ng·g-1which is0.12-4.76times than that using ASE (10-50ng·g-1) recommended by national standards. The optimized method was applied to determine pesticide residues in tea samples from different region in China. The result demonstrated a relatively strong agreement with those generated by the conventional approach. HS-SPME/GC-IDMS procedure is simple, precise, reliable and solvent saving.4. A precise and accurate analytical method for the determination of12incurred pesticides in tea using ASE by gas chromatography-high resolution isotope dilution mass spectrometry was developed. The extraction efficiency of accelerated solvent extraction (ASE) was evaluated in which four extraction parameters, solvent, temperature, static cycle and time for spiked and incurred samples, have been investigated systematically. The results imply that the extraction condition of spiked tea sample is different from that of incurred samples and the recover) from spiked tea sample may not represent the real extraction efficiency of incurred samples. The method is effective, quick, sensitive and reproducible. The result which was in agreement with the given reference concentration range has been showed that the developed method is more suitable for the precise and accurate determination and research of pesticides incurred in tea.5. An isotope dilution mass spectrometry (IDMS) method for determination of mid-polarity pesticides (β-endosulfan and endosulfan sulfate) in tea has been established. Based on the above results, the extraction time of soxhlet extraction and the purification of GPC were further optimized. Moreover, the conditions of obtaining high precision were also studied, such as the choice of injection, the voltage of electron multiplier, and the addition of the isotopic internal standard solution. The detection results of P-endosulfan and endosulfan sulfate in the CCQM-K95sample were679.724ng·g-1and455.063ng·g-1, respectively. The validation method provided good RSDs with0.396%for β-endosulfan and0.554%for endosulfan sulfate. The results were in agreement with the given reference concentration range of CCQM K95, indicating that the method is suitable for the precise and accurate determination of mid-polarity pesticides in tea. With good repeatability and precision, the method will be successfully applied to the accuracy qualitative and quantitative analysis of mid-polarity pesticides in tea.6. Production and evaluation of reference material for incurred residues of11pesticides in tea sample has been performed. The assigned reference values of the reference material were determined by highly precise isotope dilution-high resolution gas chromatography-mass spectrometry (ID-HRGCMS) method, single quadrupole gas chromatography mass spectrometry and gas chromatography mass spectrometry, and the associated expanded uncertainties were estimated from the homogeneity studies, stability testing, and the precision of the IDMS method. The reference material is an important quality assurance tool for method validation processes and quality assurance for residual pesticide analysis in tea matrices for laboratories. |
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