Studies On Fast Analytical Method Of Pesticide Multi-Residues In Sulfo-compounds Vegetables

The presence of pesticide residues in food which is crucial to human's life is one of the serious food safety problems that has greatly attracted govemment and organization's concern. Pesticide residues in vegetable have higher toxicity than that in other food. So it is important to develop analytical methods for pesticide residues in vegetable increasingly. But there are many sulfo-compounds in Allium plants, which influence the detection of pesticides in garlic etc. Therefore, it is necessary to research a analytical method for pesticide residues in Allium plants.The paper focused on the study of sulfo-compounds that influence the detection of pesticide residues in Allium plants and seted up a facility analysis method which is rapid, convenient and economical to test pesticide multi-residues in Allium plants samples. The analytical procedure was based on preventing formation of sulfur-containing compounds in Allium samples by microwave inactivation of the enzyme alliinase. The Allium samples that had been pretreated were extracted with acetonitrile and cleaned by solid-phase extraction, then pesticide residues in Allium samples were detected by gas chromatography/mass spectrometry. The details of the contents and results of the study are as follows:1. The various conditions that decreased alliinase activity, including L-cysteine, Cu²⁺ ion, freezing, heated by water-bath and microwave, had been studied and two effective methods for deactivating alliinase such as heated by water-bath and microwave had been choosed. The results of this research indicated that L- cysteine and Cu²⁺ ion couldn't sufficiently decrease alliinase activity in short time, Alliinase could be inhibited after freezed but its activity would resume at room temperature. Alliinase activity could be destroyed by water-bath and microwave. The method that suited to test pesticide multi-residues could effectively minimize the interferences caused by sulfur compounds.2. The stability of 100 pesticides which heated by water-bath (80℃and boil-bath) and microwave had been compared, and the optimal pretreatment method had been selected. The experiment showed that part of pesticides could be degraded by water-bath. Although pesticides heated by microwave had little degradation , pesticide residues in sample could be detected accurately if the heating time by microwave had been controled strictly. Therefore pretreatment with mivrowave was applied to the analysis of pesticide residues in Allium plants.3. The extraction solvent, method and the conditions of cleaning up and evaporating had been discussed. Contrasting extracting's efficiency, acetonitrile which had good extracting's efficiency was selected to extract pesticides from sample with homogenizer. Florisil SPE column was determined in cleaning process with acetone/n-hexane (1:9 v/v). Rotary evaporator and nitrogen evaporator were used in different steps.4. Chromatographic conditions were optimized. The GC-MS conditions were determined in this study. The 99 pesticides were divided into two groups according to their retention time in the column, and object ions were choosed. Methods of identifiability and quantify were determined.5. The reliability of the test method was verified. Recoveries of 99 pesticideswere obtained by various samples. All pesticide recoveries ranged from 70 to 110% and relative standard deviations were in the range 1.2～11.3% for spiked samples. The limits of quantification below 0.02 mg kg^-1 were achieved with this procedure.