Residue Analysis And Digestion Dynamics Study Of 10% Refined Quizalofol EC On Tobacco

In this paper, a pretreatment using acetonitrile for extraction and dispersive solid-phase extraction for cleanup coupled with ultra-performance liquid chromatography(UPLC) method was investigated for the determination of quizalofop-p-ethyl residues in tobacco and soil. The dissipation dynamics and terminal residues of quizalofop-p-ethyl(EC, 10%) in tobacco and soil were carried out. The results could help provide a theory reference for the safe use and standards for residue limits of quizalofop-p-ethyl on tobacco plants.For tobacco and soil samples, a modified QuEChERS method was used. Homogenized soil, green and cured tobacco leaf samples were weighed into a 50-m L centrifuge tube,then added with acetonitrile and sodium chloride. The mixture was vigorously shaken on a vortex mixer and then centrifugated at 6000 r/min. Half of the upper layer was collected and evaporated to near dryness. For soil samples, the residue was dissolved in 1 mL of methanol without further purification and then analyzed using UPLC. For tobacco samples, the residues were dissolved in ethyl acetate, transferred to another pearshape bottle and evaporated to near dryness. The residues were dissolved in 1 mL of methanol and transferred into a 2-m L centrifuge tube containing C18 and PSA. The tube was then centrifuged after vortexing. The supernant was filtered through 1 nylon filter and then analyzed using UPLC. The soil and tobacco samples were detected using UPLC with an ACQUITY UPLC? BEH C18 column. The quantitative analysis was external standard method. Quizalofop-p-ethyl was successfully separated in 8 min.The results showed excellent linearity with correlation coefficient of 1.0000 was found at the range of 0.1-50.0 ?g/m L. The limit of detection(LOD) of quizalofop-p-ethyl was 1.8×10-10 g and the limit of quantification(LOQ) was 0.02 mg/kg. At the spiked levels of 0.02-25.00 mg/kg, recoveries for quizalofop-p-ethyl ranged from 78.94% to 105.20% with a relative standard deviation of 1.80%-5.30%. The LOQ of soil, green and cured tobacco leaves were 0.02 mg/kg, 0.20 mg/kg and 0.50 mg/kg, respectively. The established method was simple and timesaving, which was suitable for the analysis of quizalofop-p-ethyl in tobacco and soil.The dissipation dynamics and terminal residues of quizalofop-p-ethyl(EC, 10%) in tobacco and soil were carried out in Guizhou and Shandong provinces during 2014 and 2015. The results indicated that initial concentrations of quizalofop-p-ethyl in soil were <0.02 mg/kg. The dissipation rates in green tobacco leaves were >90% in Guizhou and Shandong, 1 day after application in 2014 and 5 days after application in 2015. The dissipation data were only used for monitoring. In the terminal residue experiment, the concentrations of quizalofop-p-ethyl residue in cured tobacco leaves were lower than 0.50 mg/kg(LOQ) on the harvest time after one application of two dosages. Therefore, a dosage of 60~90g a.i/ha was recommended, which could be considered as safe to human beings.In addition, a liquid chromatography coupled with tandem mass spectrometry(LC-MS/MS) method was also developed to determine the residues of quizalofop-p-ethyl in soil. In the indoor degradation simulation experiment, different environment factors which might influence on the degradation of quizalofop-p-ethyl in different soils were investigated. The preliminary degradation pattern was obtained which could help evaluate potential environmental risk of quizalofop-p-ethyl and provide theoretical basis for restoration study.