Abstract: Purpose: To develop a method for the determination of diafenthiuron residue in tea by liquid chromatographytandem mass spectrometry (LC-MS/MS). Methods: The diafenthiuron in tea was extracted by acetonitrile and purified by the quick, easy, cheap, effective, rugged and safe (QuEChERS) method. The separation of the analyte was performed on a C18 column by gradient elution using a mobile phase consisting of acetonitrile and water (containing 0.1% formic acid). The mass spectrometer was operated with electrospray ion source in positive mode (ESI+) by selective reaction monitoring (SRM), and the analyte was quantified by the external standard method. Results: Low recoveries of diafenthiuron obtained by the method described in GB/T 23205?2008 was in part ascribed to the decomposition of diafenthiuron in the pretreatment processes. A good linearity (r = 0.999 9) was observed over the range of 1.0 to 500 μg/L using the new method developed in this study. The limit of quantification (LOQ) was 0.01 mg/kg, and the recoveries at three spiked levels (0.010, 1.0 and 5.0 mg/kg) varied from 83.3% to 99.4%, with relative standard deviations (RSDs) of 1.87%–6.30%. Conclusion: This method is simple and convenient, and it can effectively avoid the influence of diafenthiuron decomposition in the pretreatment process, and thus can be applied for the qualitative and quantitative confirmation of diafenthiuron residue in tea.

Key words: tea, diafenthiuron, liquid chromatography-tandem mass spectrometry (LC-MS/MS), QuEChERS