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) ≥0.99 were obtained at the concentration levels of 10, or 50 to 1,000 μg ml^?1. The limits of quantifications (LOQs) were 5–25 μg ml^?1, respectively. The recovery rates of samples spiked with 20, 100, and 200 μg 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).