Determination of clothianidin residues in garlic by liquid chromatography-tandem mass spectrometry combined with QuEChERS

Clothianidin, a neonicotinoid insecticide, has been applied to broadly control agricultural pests, such as Delia antique. However, few methods for determination of clothianidin in garlic samples have been published so far. In this study, a rapid, sensitive, and environmental-friendly residue determination method based on QuEChERS for analysis of clothianidin residues in garlic was investigated. The analytes were extracted from the samples using acetonitrile combined with homogenization, purified by dispersion solid phase matrix extraction using ODS-C18, PSA and florisil. Then samples were analyzed by LC/MS/MS with multiple-reaction monitoring (MRM) directly. The content was determined by external standard method. A good linear calibration curve was exhibited over a concentration range of 1.0 to 100 µg/L for clothianidin with a correlation coefficient of 0.9995. Average recoveries for clothianidin in garlic were 95.7%~100.7% with a relative standard deviations (RSD) of 0.7%~4.3% at spiked levels of 5~50 µg/kg. For clothianidin, the limit of quantification (LOQ) was 1.55 µg/kg and the limit of detection (LOD) 0.47 µg/kg. Then dissipation of clothianidin was studied by the method above at two dosage of 750 g a.i./ha (the recommended dosage) and 1500 g a.i./ha. In the garlic samples, the concentrations of clothianidin were 0.037 and 0.078 mg/kg, respectively, 7 days after treatment and then decreased rapidly, reached 0.009 and 0.015 mg/kg after 14 days (d). The residues in garlic bulb only 21 days after treatment were 0.003 and 0.011 mg/kg, respectively, less than the MRLs (0.02 mg/kg in garlic) set by Japan’s “Positive List System”.