Determination of 12 Pesticides in Tea by Liquid Chromatography- Tandem Mass Spectrometry with Dispersive Solid Phase Extraction

A method for the determination of 12 pesticides in tea by liquid chromatography-tandem mass spectrometry with dispersive solid phase extraction was proposed. The tea sample powder (2 g) was extracted by 10 mL of acetonitrile, and purified by 0.4 g of ethylenediamine-N-propyl silane (PSA). Twelve pesticides were separated by Agilent ZORBAX SB-Aq column as stationary phase and acetonitrile-0.1% (volume fraction) formic acid solution containing 5 mmol·L^-1 ammonium acetate as mobile phase system. Electrospray ion source with positive ion mode was used for scan, multi-reaction monitoring mode was used for detection, and matrix matching mixed standard solution series were used for drawing working curves, with quantification by external standard method. It was shown that linear relationships between the mass concentrations and peak areas of 12 pesticides were kept in definite ranges, with detection limits (3S/N) in the range of 0.3-3 μg·kg^-1. Test for recovery was made on negative sample at 3 concentration levels by standard addition method, giving results in the range of 80.0%-118%, and RSDs (n=6) of the determined values ranged from 1.3% to 11%. The method was applied to analysis of 70 actual tea samples, and difenoconazole, dimethomorph, triadimefon, propiconazole and tebuconazole were detected, with detection amounts in the range of 1.1-1 220.0 μg·kg^-1. The detection rate of difenoconazole was the highest, and the total detection rate was 62.9%.