Risk Assessment and Residue Analysis of Bifenazate in Tea by UPLC-MS/MS

A convenient and sensitive residue analysis method for bifenazate in fresh tea leaves and made tea was developed and validated by ultra high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UPLC-MS/MS) followed by dispersive solid phase extraction cleanup. The calibration curve is linear over the concentration of 0.002 5-1.00 mg/L for bifenazate with the correlation coefficient (r) of 0.994 2. The average recoveries of bifenazate at three spiked concentration levels (0.020, 0.20, 2.0 mg/kg) in green tea sample matrixes are 79.3%, 88.6% and 103.4% with the relative standard deviations (RSDs) of 6.1%, 5.9% and 3.7%, in black tea sample matrixes are 79.3%, 82.6% and 103.3% with RSDs of 6.7%, 4.5% and 4.7%, in fresh tea leaves are 91.1%, 94.4% and 91.0% with RSDs of 4.3%, 3.8% and 7.6%, respectively. The limit of detection (LOD, S/N=3) of befenazate is 1.5 μg/kg，and the limit of quantitation (LOQ, S/N=10) of bifenazate in different matrixes is 5 μg/kg. This proposed method was successfully applied in the degradation and final residue study of 43% bifenazate suspension concentrate (SC) in the field treatment experiment. The degradation half-life time of bifenazate in fresh tea leaves is in the range of 1.4-2.9 days. According to the recommended dose and the 1.5 times of recommended dose after 1-2 times, the results show that the final residual amount of bifenazate in made tea after 10 days is less than 5 mg/kg. According to the results of risk assessment, it is suggested that the maximum residue limit (MRL) of bifenazate in tea can be set to 5 mg/kg for tea drinking with the pre-harvest intervals (PHI) of 10 days, this is a safety threshold for the human body.