| In current work, we developed a LC-MS/MS method to determine the dimethomorph residue of 30% dimethomorph?prochloraz(suspension concentrate, SC) in tobacco matrix. Prochloraz was determined by a gas chromatograph with an electron capture detector(GC-ECD). the residue determination and degradation in tobacco and soil were investigated to provide theoretical basis for safe appalication and residue detection of 30% dimethomorph?prochloraz(suspension concentrate, SC).Dimethomorph in tobacco and soil samples were extracted with methanol by ultrasonic, MgSO4 and Na2SO4 was subsequently added, and the tube was shaken vigorously by hand and centrifuged, upper layer was purified by C18 and PSA after constant volume; Tobacco powder were extracted with water(0.1% formic acid) and methanol by ultrasonic, add MgSO4 and Na2SO4, and the tube was shaken vigorously by hand and centrifuged. Upper layer was purified by C18 and PSA after constant volume, separated by Phenomenex Luna C18 column, then the residues of Dimethomorph was determined by LC-MS/MS. The results showed that the external standard curve had a good linearity between 0.0010~0.9900 ?g/mL with the correlation coefficient of 0.99. The average recovery of dimethomorph ranged from 74.88 to 78.53% with a relative standard deviation(RSD) of 1.30 to 5.91% at fortification levels of 0.020?0.20?2.0 and 50.0 mg/kg in fresh tobacco; that ranged from 87.15 to 93.66% with an RSD of 1.21 to 5.41% at fortification levels of 0.010?0.10 and 1.0 mg/kg in soil, and that ranged from 80.33 to 83.86% with an RSD of 1.91 to 4.17% % at fortification levels of 0.050?0.50 and 5.0 mg/kg in tobacco powder. The limit of detection(LOD) was 3.7×10-13 g at a signal-to-noise(S/N) ratio of 3. The limit of quantification(LOQ) of the proposed method for dimethomorph was 0.020 mg/kg?0.010 mg/kg and 0.050 mg/kg in tobacco soil and tobacco powder, respectively.Prochloraz in tobacco(or soil and tobacco powder) samples were extracted with hydrochloric acid and acetone, then reacted with pyridine hydrochloride at high temperature, the product 2, 4, 6-TCP was was determined by GC-ECD. The results showed that the external standard curve had a good linearity between 0.1008~10.08 ?g/mL with the correlation coefficient of 0.99. The average recovery of prochloraz ranged from 77.84 to 83.27% with a relative standard deviation(RSD) of 2.46 to 4.20% at fortification levels of 0.020?0.20 and 2.0 mg/kg in fresh tobacco; that ranged from 76.59 to 82.21% with an RSD of 5.11~7.48% at fortification levels of 0.010?0.10 and 1.0 mg/kg in soil, and that ranged from 74.92 to 80.26% with an RSD of 2.40 to 8.77% at fortification levels of 0.050?0.50 and 5.0 mg/kg in tobacco powder. The limit of detection(LOD) was 1.2×10-9 g at a signal-to-noise(S/N) ratio of 3. The limit of quantification(LOQ) of the proposed method for prochloraz was 0.020 mg/kg?0.010 mg/kg and 0.050 mg/kg in tobacco soil and tobacco powder, respectively.The field trials of 30% dimethomorph?prochloraz(suspension concentrate, SC), including the dissipation and terminal residue experiments in tobacco and soil, were conducted in Huishui(Guizhou Province) and Changsha(Hunan Province) in China between 2014 and 2015. The half-life of dimethomorph varied from 1.7 to 7.8 days in tobacco and no rules in soil, respectively. The terminal residue of dimethomorph at preharvest intervals(PHI) of day in tobacco changed from 0.06-0.59 mg/kg and from <0.03-0.51 mg/kg in soil, respectively. The half-life of prochloraz varied from 3.3 to 8.2 days in tobacco and 2.1 to 8.0 days in soil, respectively. The terminal residue of prochloraz at pre-harvest intervals(PHI) of day in tobacco changed from <0.05-0.14 mg/kg and from <0.01-0.12 mg/kg in soil, respectively.Considering that no MRL of dimethomorph and prochloraz in tobacco from FAO, CAC, WHO, and China has been established, the present study would be helpful for FAO, CAC, WHO, and the Chinese government to establish MRL for dimethomorph and prochloraz in tobacco and other crops and provide guidance on the proper and safe use of this fungicide. |
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