LC-MS/MS Determination of Residual Amounts of 5 Neonicotinoid Pesticides in Tea with Dispersive Solid Phase Extraction Using Multiwalled Carbon Nanotubes as Adsorbent

LC-MS/MS was applied to the determination of residual amounts of 5 neonicotinoid pesticides, i.e. acetamprid,clothiaindin,imidacloprid, thiacloprid and thiamethoxam in tea with dispersive solid phase extraction using multiwalled carbon nanotubes as adsorbent. The tea sample after comminution was immersed with water for 30 min, and then extracted with acetonitrile. Multiwalled carbon nanotubes were used as adsorbent to remove impurities. Agilent C₁₈ chromatographic column was used as stationary phase, and the mixture of 5 mmol·L^-1 ammonium acetate-0.1% (φ) formic acid solution and methanol mixed in different ratios was used as mobile phase in gradient elution. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Linear relationships between values of peak area and mass concentration of the 5 neonicotinoid pesticides were kept in the same range of 1.0-20 μg·L^-1, with the same lower limit of determination (10S/N) of 0.01 mg·kg^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 80.5%-98.7%, with RSD's (n=6) in the range of 5.0%-13%.