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.