Residue determination of pyraclostrobin, picoxystrobin and its metabolite in pepper fruit via UPLC-MS/MS under open field conditions

In this study, a new, high-efficiency and sensitive method was determined to simultaneous analyze the residue of pyraclostrobin, picoxystrobin and its metabolite BF-500-3 in pepper fruit using modified QuEChERS pretreatment combined with ultra performance liquid chromatography tandem mass spectrometry. The clean-up steps of QuEChERS procedure were optimized using the chemometric tools. Models of stepwise regression and surface response demonstrated that the optimal sorbent mixtures were 40 mg nano-zirconia + 10 mg C-18 for Pyraclostrobin and picoxystrobin and 30 mg nano-zirconia + 20 mg C-18 for BF-500-3. The optimized purification procedures provided satisfactory recoveries for all tested fungicides with rates between 91% and 107% and relative standard deviations between 3.7% and 9.6%. The limits of detection and quantification were in the range of 0.0360-0.272 mu g/kg and 0.120-0.910 mu g/kg. Based on this method, the dissipation of pyraclostrobin, picoxystrobin and its metabolite in pepper fruit were determined under field conditions. Pyraclostrobin and picoxystrobin degraded rapidly with half-lives of 5.53-7.02 and 5.97-7.82 days and 5.09 and 5.68 days in 2016 and 2017, respectively. The residue levels of BF-500-3 increased first and then decreased. The terminal residues of all fungicides were below the maximum residue limits (MRLs). This research can not only provide guidance for the reasonable usage of pyraclostrobin and picoxystrobin in agriculture but also give a reference for the Chinese government to establish the MRL for pyraclostrobin in pepper.