Residue and dissipation of thiamethoxam in tobacco by high performance liquid chromatography

A new method using high performance liquid chromatography-ultraviolet detector (HPLC-UV) was developed to analyze thiamethoxam residue in fresh tobacco leaves and cured tobacco leaves. Samples were extracted with acetonitrile, cleaned up by solid phase extraction column (SPE), and detected by HPLC-UV with quantification by external standard method. The result shows that when thiamethoxam was spiked at 0.01-5.0 mg/kg levels in fresh tobacco leaves and 0.05-5.0 mg/kg levels in cured tobacco leaves, the average recoveries of thiamethoxam were 92%-95% and 91%-94%, with relative standard deviations (RSDs) of 4.5%-9.2% and 5.9%-6.8%. The limit of quantification (LOQ) of this method was 0.01 mg/kg in fresh tobacco leaves and 0.05 mg/kg in cured tobacco leaves. Field experiments were performed in Qingdao, Shandong Province and Changsha, Hunan Province. Dynamic results showed the half-live of thiamethoxam in green tobacco leaves was 1.3-8.1 d. When sprayed with 2 and 3 times dosages of 18.9 and 28.4 g a.i./hm at the bud stage to maturity stage of tobacco, residues in cured tobacco leaves after 7 days in all treatment ranged from 0.05 to 0.80 mg/kg, which were all below MRL value set by CORESTA (5.0 mg/kg).