Residue and decline of spinosad in cabbage and soil by high-performance liquid chromatography-tandem mass spectrometry

An efficient,rapid and sensitive analytical method was developed for the determination of spinosad in cabbage and field soil by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).Its decline and residue behavior in cabbage and soil were also evaluated.Samples were primarily extracted by acetonitrile,cleaned up with PSA dispersive solid phase extraction (DSPE) and finally analyzed by HPLC-MS/MS.The limit of detection and limit of quantification were 6×10-12 g and 0.005 mg/kg respectively in both cabbage and soil.Average percentage of recovery,RSDs were 87%-95%,6%-10% in cabbage and 86%-100%,4%-8% in soil respectively.Experiments in Beijing,Anhui and Hunan were conducted in 2011.The results showed decline of spinosad both in cabbage and soil,which were well fitted with the first-order kinetics,and the half-lives were 0.83-1.16 d and 0.88-1.17 d,respectively.The final residue experiment were conducted in 2010 and 2011.The results showed that at the recommend dosage and 1.5 times the dosage 26.25 and 39.38 g(a.i.)/hm2,residues in cabbage after 1 day in both treatments were all below MRL value(2.0 mg/kg,by China).