Abstract:

A high performance liquid chromatography-triple quadrupole tandem mass spectrometry （HPLC-MS/MS）method was established for the simultaneous determination of residues of flonicamid and its three metabolites，as well as spirotetramat and its four metabolites in kiwifruits and soil. The cleanup sorbents was optimized. The samples were extracted by acetonitrile with 1% acetic acid，cleaned-up by octadecyl bonded silica gel（C18），and detected in multiple reaction monitoring（MRM）mode. The good linear relationships were obtained for the nine target compounds within the mass concentration range of 0.005-1.000 mg · L^-1，and the determination coefficients were 0.9921 to 0.9999. The matrix effects in kiwifruits and soil were 0.04-1.04，and the matrix-matched calibration curves were used for quantification. At the spiking levels of 0.005-0.500 mg · kg^-1，the average recoveries were 71%-117%，and the relative standard deviations were 0.3%-10.5%. The method was suitable for rapid detection of flonicamid and its three metabolites，as well as spirotetramat and its four metabolites residues in kiwifruits and soil. The results of the residue tests showed that the degradation dynamics of flonicamid and spirotetramat in kiwifruits and soil followed the first-order kinetic equations. Compared to individual applications，mixed applications had an impact on the half-lives of flonicamid in both kiwifruits and soil，while it had no significant effect on spirotetramat. The residual amount of the metabolites of spirotetramat，especially the metabolite S-enol，significantly increased or even exceeded that of the parent in the soil under the mixed application condition. The final residue results showed that the residues of flonicamid and its metabolite TFNG，as well as spirotetramat and its metabolites S-mono，S-keto and S-enol were detected in kiwifruit samples，and the residues ranged from 0.005 to 3.445 mg · kg^-1. However，only residues of two metabolites of spirotetramat，S-keto and S-enol，were detected in the soil，and no other compounds were detected. Correlation analysis showed that the residual amounts of flonicamid，spirotetramat and their metabolites in kiwifruits and soil were positively correlated with the dosage and frequency of application，and were negatively correlated with the harvest interval. The results of dietary risk assessment indicated that the short-term dietary intake risk of flonicamid and spirotetramat was acceptable. The residues of spirotetramat had no long-term dietary risk to the general population，while flonicamid might pose a long-term dietary risk to the general population.

Key words: flonicamid, spirotetramat, pesticide residue, kiwifruit, metabolites, joint application, risk assessment