Abstract:

A pretreatment method of dichloromethane plus hot water（45℃）extraction followed by cleanup with Carbosil cartridge (for organophouros pesticides residues) or Florisil cartridge (for pyrethrosins residues) was developed for eliminating the disturbance of caffeine to the GC determination of pesticides residues in tea. A single laboratory validation was performed by spiking organophouros and pyrethrosins pesticides at three levels (0.2, 0.8, and 1.6 mg/kg, respectively). The results showed that the caffeine was effectively removed from tea extract by this method. The average recoveries for organophouros pesticidies were between 73% and 112.9%, the RSDs were less than 8%, and the limits of detection ranged between 0.02 and 0.002 mg/kg; for pyrethrosins, the average recoveries varied between 78.8% and 105%, the RSDs were below 9%, and the limits of detection ranged from 0.001 to 0.006 mg/kg. The accuracy, precision and limit of detection of this method for all these pesticides are in agreement with even higher than the standards set by the related Chinese and EU regulations.

Key words: tea, organophosphorus pesticides residues, pyrethrosin residues, caffeine