High-Performance Liquid Chromatography and Gas Chromatography — Mass Spectrometry Methods for the Determination of Imidacloprid, Chlorpyrifos, and Bifenthrin Residues in Tea Leaves

□ A sensitive, rapid, and reproducible high-performance liquid chromatography–diode array method and a gas chromatography/mass spectrometry method were developed to determine imidacloprid, chlorpyrifos, and bifenthrin in tea leaves. Solid-phase extraction (SPE) was employed for sample preparation. The extraction solvent used was acetonitrile:toluene (3:1, v/v). Linearity was observed in tea spiked with 0.4–6.0 µ g mL−1 (n = 6) of imidacloprid, 0.8–15.0 µ g mL−1 (n = 6) of chlorpyrifos, and 0.3–6.6 µ g mL−1 (n = 6) for bifenthrin. The correlation coefficients obtained were higher than 0.99 for all pesticides. The limits of detection for imidacloprid, chlorpyrifos, and bifenthrin were 0.06, 0.12, and 0.05 mg kg−1, respectively. The limits of quantification for imidacloprid, chlorpyrifos, and bifenthrin were 0.20, 0.40, and 0.17 mg kg−1, respectively. Recoveries of the analytes were between 80% and 96% with RSDs <10% (intra-day and inter-day). The methods were applied to monitor pesticide residues in tea. The results obtained by both techniques indicated that their feasibility for practical applications.