| The analysis of pyraflufen-ethyl residues in leaves, cottonseed and soil was established in this dissertation. The storage stability of pyraflufen-ethyl in cottonseed was analyzed. The dynamics of pyraflufen-ethyl in leaves under field conditions was studied. The degradation rule and influencing factors of pyraflufen-ethyl residues in soil under laboratory conditions were analyzed. The safety evaluation of pyraflufen-ethyl residues in cottonseed was investigated. The main results were summarized as following:1. The analytical methods for pyraflufen-ethyl residues in leaves,cottonseed and soilLeaves and cottonseed samples were extracted by acetonitrile for 2 times,and cleaned up with GCB/PSA SPE column; soil samples were extracted by acetone for 2 times after wetted, and cleaned up with C18 SPE column;Pyraflufen-ethyl in samples was determinated by HPLC with PDA detector.Determination conditions:Shimadzu LC-20AT high performance liquid chromatography equipped with PDA, Column:250mmx4.6mm,5μm Agilent SB-C18, detector wavelength:243nm, mobile phases:acetonitrile and water (65:35,v/v), flow velocity:1mL/min, Oven temperature:30℃. The retention time of pyraflufen-ethyl was about 6.8min. The limit of instrumental detection was 4.0×10-10 g.Extraction system:Comparing the residue analysis results of pyraflufen-ethyl with acetonitrile and acetone, we selected acetonitrile as the optimized extract solvent in leaves and cottonseed; Comparing the residue analysis results of pyraflufen-ethyl with mechanical oscillation and ultrasonic oscillation, we selected mechanical oscillation for 30minutes + 20minutes as the optimized extract method; Comparing the residue analysis results of one, two and three extract times, we selected extract two times as the optimized extract times. Analytical method of soil referenced existing methods.Clean-up system:Clean up of leaves and cottonseed, comparing the purifying effect and residue analysis results of pyraflufen-ethyl with liquid-liquid extraction, C18 SPE column and GCB/PSA SPE column, we selected GCB/PSA SPE as the purified column, used 4mL acetonitrile as the elute solvent and collected 6mL acetonitrile. Clean-up of soil on the basis of reported methods by using C18 SPE column, firstly selected 3mL acetonitrile-water (5:5, v/v) as the elute solvent and collected 6mL acetonitrile.The experiments of fortified samples:Three different concentrations of 0.05mg/kg, 0.1mg/kg, 1.0mg/kg were fortified respectively in leaves and soil, and 0.02mg/kg, 0.1mg/kg, 1.0mg/kg were fortified in cottonseed. The average recoveries of pyraflufen-ethyl in leaves were ranged between 93.94%～101.65%, and the RSD ranged between 3.96%～8.06%. The average recoveries and RSD in cottonseed were ranged between 84.88%～98.62% and 7.59%～10.47%. The average recoveries and RSD in soil were ranged between 85.49%～90.71% and 5.59%-8.16%. The LOQ of pyraflufen-ethyl in leaves, cottonseed and soil were all 0.02 mg/kg. This results showed that the method accorded with demands of pesticide residue analysis.Storage stability of pyraflufen-ethyl in cottonseed:The results of the storage stability at 4℃ indicated that, under condition of 0.1mg/kg fortified level in cottonseed, the dynamic equation was C=0.1013e-00098t, and the half-live was 70.71d. The degradation rate of pyraflufen-ethyl was 16.84% after the storage of 30d,43.63% after 60d, and 57.39% after 90d, respectively. The residues of pyraflufen-ethyl in cottonseed were <LOQ after 120d.2.Dynamics of pyraflufen-ethyl residues in leavesThe dissipation of pyraflufen-ethyl in leaves was studied in Ahui and Shandong in 2012 and 2013. The residues of pyraflufen-ethyl in leaves were 0.455mg/kg-0.913mg/kg in Anhui. In 2012, the foliar deposition was maximum in 3d after application. The dissipation rate of pyraflufen-ethyl was 64.40% after 5d. Leaves fell off after 7d; In 2013, the foliar deposition was maximum in 3d after application. The dissipation rate of pyraflufen-ethyl was 25.63% afte 5d, and was 70.43% afte 7d. Leaves fell off after 14d.The residues of pyraflufen-ethyl in leaves were 0.085mg/kg-3.261mg/kg in Shandong. In 2012, the foliar deposition was maximum in 3d after application. Leaves fell off after 5d.; In 2013. the foliar deposition was maximum in 1d after application. The dissipation rate of pyraflufen-ethyl was 24.71% afte 3d. Leaves fell off after 5d.3.Dynamics of pyraflufen-ethyl residues in soil under laboratory conditionThe results of the residue experiments in soil under laboratory conditions indicated that, the degradation procedure of pyraflufen-ethyl was correspond to the mathematic pattern. In clay, the dynamic equation was C=2.46765e-0.5435t, and half-life was 1.28d; In sterile clay, the dynamic equation was C=2.7428e-0.2251t, and half-life was 3.08d; In sterile clay, the dynamic equation was C=2.8106e-0.4642t, and half-life was 1.49d; In sterile clay, the dynamic equation was C=3.1109e-0.2177t, and half-life was 3.18d.The result indicated that, the influence of microorganism on the residue of pyraflufen-ethyl was great. The half-life was longer in sterile soil, and was about 2.1～2.4 times compared with untreated soil. As the half-lives were 1.28d in clay and 1.49d in sandy soil, we could see that, the half-lives were short in both types of soil, the degradation rate of pyraflufen-ethyl is in clay was slightly fast than in sandy soil. This could be due to the organic content of soil, pH and other factors, which affected the degradation of pyraflufen-ethyl.4.Safety evaluation of pyraflufen-ethyl residues in cottonseedThe results of the residue experiments for two years at two points in Anhui and Shandong indicated that, all the sample were not detected with pyraflufen-ethyl under the dosage of 6 g a.i./ha used, but were detected under the dosage of 9 g a.i./ha. The residues of pyraflufen-ethyl were <LOQ～0.041mg/kg in Anhui, and were <LOQ～0.033mg/kg in Shandong. As there was no MRL of pyraflufen-ethyl in cottonseed existing in our country, refer to the MRL of America (0.04mg/kg), we could see that, it was safe used under the dosage of 300g/ha (6 g a.i./ha), which the residue of pyraflufen-ethyl in cottonseed after harvest time was bellow official limit. |
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