A Modified QuEChERS Sample Preparation Method for the Analysis of 70 Pesticide Residues in Tea Using Gas Chromatography-Tandem Mass Spectrometry

A modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method for the simultaneous determination of 70 pesticides in tea was developed using gas chromatography-tandem mass spectrometry. Prior to acetonitrile extraction of the target compounds from tea matrix, samples were soaked in distilled water to improve the extraction efficiency. A mixture of adsorbents containing primary-secondary amine, octadecylsilane, graphite carbon black, and multiwalled carbon nanotubes was applied for the cleanup. Additional steps of concentration and solvent exchange were performed to reduce the amount of co-extracts and to decrease the limit of detection of the method. For all pesticides, good linear calibrations with coefficients (R (2)) a parts per thousand yen0.99 were obtained at the concentration levels of 10, or 50 to 1,000 mu g ml(-1). The limits of quantifications (LOQs) were 5-25 mu g ml(-1), respectively. The recovery rates of samples spiked with 20, 100, and 200 mu g kg(-1) of analytes ranged from 71 % to 105 %. In addition, the relative standard deviations were lower than 20 %. A total of 331 tea samples were analyzed using this method, and the levels of five pesticide residues in nine tea samples exceeded the strictest maximum residual limits (MRLs).