| Tea has health care function. It can eliminate free radicals to delaying senescence, inhibit cardiovascular disease, prevent cancer and inhibit bacterial resistance and so on. However, in the process of tea-planting, yield and quality of tea has decreased gradually due to insect damage. People use a lot of pesticides in order to prevent pests, which cause the problem of pesticide residues. In recent years, with the improvement of foreign technical barriers,especially after the implementation of Japan’s positive list, export residue detection requirements were increased. Thus the requirement of China’s tea export inspection was higher. But the detection system could have only test tea so far, the detection of fresh leaves of tea was still in blank period. In the experiment, we detected the peaticide residue of fresh leaves of tea, which may effectively reduce the loss of manufacturer and improve the quality and safety of tea in China. Therefore it is very important to strengthen the detection of pesticide residues in fresh leaves of tea.In the experiment, we studied the extraction, purification technology and Gas chromatographic detection conditions of 20 kinds of organic chlorine commonly used in fresh leaves of tea and pyrethroid pesticides. We established 20 kinds of organic chlorine determination of tea fresh leaves by gas chromatography and the method of pyrethroid pesticides. The main results are as follows:(1)The optimization of chromatographic conditions. Through the optimization of chromatographic conditions,we determined to use DB-5 capillary column(30 mm x 0.32 mm and 0.25 μm), temperature programme: 180oC(remain 3 min)(3oC/min)→240oC(remain27min). The column flow rate is 2mL/min, the inlet temperature of 250 oC, detector uses ECD detector, its temperature is 280 o C, tail blowing is 30mL/min, sample size is 1μL, split ratio is5:1.Under gradient elution conditions of the experiment, 20 kinds of pesticides were separated by gas chromatography, and then be measured in ECD detector. 20 kinds of organochlorine and pyrethroid pesticides are in good linearity in the range of 5 to 100 g/L, the correlation coefficient is 0.9981- 0.9998.(2)To optimize the pretreatment conditions for analysis of pesticide residues in fresh leaves of tea. We optimized the processing method of SPE from six aspects, which were the types and dosage of extraction solvent, extraction method, SPE column packing and the type and amount of solvent elution. Then we determined the optimal SPE pretreatment methods:30mL acetonitrile, homogenization extraction, the TPT column purification, 20 m L of acetonitrile: toluene(3:1, v/v) solution was leached and eluant was collected, using nitrogen blowing concentrated, constant volume of acetonitrile, membrane filtration, the sample was measured. The approach is simple and rapid to meet the requirements of the pesticide residue detection technology.(3)Recovery of method and precision experiment. Add recovery test using the pretreatment method in 4 levels of 0.005, 0.01, 0.02 and 0.05mg/kg, each level repeated 5times. The average recovery of four concentration of fresh tea leaves was 73.18%- 100.91%,its relative standard deviation was 1.81%- 9.52%.The method had high sensitivity and good accuracy. It meet the requirements of detection technology of pesticide residues, and it provided technical support for the detection of fresh tea leaves... |
PDF Full Text Request