Dissipation, residues and risk assessment of oxine-copper and pyraclostrobin in citrus

An efficient, sensitive, simple and fast method for the simultaneous determination of oxine-copper and pyraclostrobin in citrus fruit was developed and validated. The method uses ethylene diamine tetra-acetic acid as a competitive ligand to convert oxine-copper to soluble 8-hydroxyquinoline for analysis by QuEChERS and LC-MS/MS. Linear relationships were determined with correlation coefficients ranging from 0.9904 to 0.9998. The limits of detection for the analytes were 0.012–0.8 μg kg−1, and the limits of quantitation were 0.04–2.6 μg kg−1 in citrus. The average recoveries were 79.1–114.9% with relative standard deviations of less than 7.4%. The analyses of dissipation indicated that the half-lives of oxine-copper and pyraclostrobin were 1.94–3.67 and 1.79–2.48 days and the terminal residues were <0.08–8.99 and <0.02–1.90 mg kg−1, respectively. The risk quotients of oxine-copper and pyraclostrobin were 0.026–0.199 and 0.003–0.022, respectively. This risk assessment provides a reference for the safe and reasonable use of oxine-copper and pyraclostrobin and may help to establish maximum residue limits for these pesticides in China.