Dissipation and Residual Risk of Pymetrozine in Tobacco

A new method using high performance liquid chromatography-ultraviolet detector (HPLC-UV) was developed to analyze pymetrozine residue in fresh and cured tobacco leaves. Samples were extracted with methanol, cleaned up with Solid Phase Extraction Column (SPE) of C18 and PSA, analyzed and quantified using HPLC-UV with external standards. The average recovery rate at spiked levels of 0.02-5.0 mg/kg ranged from 94.0%-99.3% for fresh tobacco leaves and 89.0%-96.1% for cured tobacco leaves, with relative standard deviations (RSD) of 0.74%-3.88% and 0.73%-3.03%, respectively. The limit of quantification (LOQ) in fresh and cured tobacco leaves were both 0.02 mg/kg. Field experiments were performed in Qingdao, Shandong Province and Changsha, Hu'nan Province. Results from dynamic analysis showed that pymetrozine level declined quickly in green tobacco leaves with half-lives of 4.2-8.8 d. The final residues of pymetrozine in cured tobacco leaves were determined after the second and third application at levels of 150 and 225 a.i.g/hm², which were all below the MRL set by CORESTA (1.0 mg/kg).