Objective  A newly modified analytical method for detecting pesticide residues in tea was developed to improve test efficiency and reduce cost.

  Method   Fe₃O₄ nanoparticles were used to replace the conventional pigment-removing material prior to measurements on pesticide residues, including carbendazim, pyrimethanil, tricyclazol, imidachloprid, acetamiprid, methomyl, and thiamethoxam, in tea by liquid chromatography-tandem mass spectrometry. The methodology was evaluated according to its applicability and validated in a spiked residue test.

  Result  The recovery rates on the 7 pesticides under the modified method using 300 mg Fe₃O₄ nanoparticles for pigment removal pretreatment were higher than graphitizing with carbon black (GCB). The pigment-removed tea extracts were separated with a Phenomenex Luna C8 (150 mm × 2.0 mm × 3.0 µm) by using 0.1 % formic acid and 5 mmol·L^-1 ammonium acetate as Phase A and acetonitrile as Phase B for the mobile phase prior to the tandem mass spectrometric analysis under the multiple reaction monitoring mode with external standards. A linearity on the measurements by the new method was achieved within the pesticide concentrations of 0-50 µg·L^-1 showing correlation coefficients (R²) greater than 0.995 for all 7 pesticides. On 5, 10, and 50 ng·g^-1 spiked pesticide samples, average recovery rates of the new method ranged from 71.6 % to 107.7 % with relative standard deviations of 3.95%-13.62 %. The limits of detection (LOD) on the pesticides by the method were between 0.15 µg·kg^-1 and 0.60 µg·kg^-1, and the limits of quantitation (LOQ) between 0.5 µg·kg^-1 and 2.0 µg·kg^-1.

  Conclusion  The newly developed pesticide detection method was stable, repeatable, and accurate for the designed purpose.