Residuesanddissipationdynamicsofchlorantraniliproleandpyraclostrobinin<italic>Dendrobiumofficinale</italic>

In this study, a simple and practical QuEChERS-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was established to measure the residues of chlorantraniliprole and pyraclostrobin in the stems and leaves of Dendrobium officinale Kimura et Migo. Samples were extracted by acetonitrile and cleaned by primary secondary amine (PSA), C₁₈ and Pesticarb (PC) sorbent. Samples were measured by LC-MS/MS operated in the positive electrospray ionization (ESI) mode, and data was collected in multiple reaction monitoring (MRM) mode. The mean recoveries of chlorantraniliprole in the stems and leaves of D. officinale were 74%-90% at the four spiking levels from 0.10 to 60 mg/kg with relative standard deviations (RSDs) of 3.2%-4.1%. The mean recoveries of pyraclostrobin were 75%-104% with RSDs of 1.7%-4.4%. The limits of quantitation (LOQs) of chlorantraniliprole and pyraclostrobin were both 0.1 mg/kg. The dissipation of chlorantraniliprole and pyraclostrobin in D. officinale was slow. The dissipation dynamic study showed that chlorantraniliprole in the stems and leaves of D. officinale degraded by 40% and 72%, respectively, after 120 d, whereas pyraclostrobin degraded by 80% and 94%, respectively. The half-life of pyraclostrobin in the leaves of D. officinale was 38.1 d. When 5% chlorantraniliprole SC was applied for 1-2 times at an interval of 7 d with dose of 37.5 g/hm², the residues of chlorantraniliprole were lower than 3 mg/kg at the 30^th day after the last spray. When 25% pyraclostrobin WG was applied for 2-3 times at intervals of 7 d with dose of 187.5 g/hm², the residues of pyraclostrobin were below 8 mg/kg 90 days after the last spray.