Determination of pyrethroid residues in fresh tea leaves by dispersive solid phase extraction and gas chromatography

A GC-ECD method based on ultrasound assisted extraction (UAE) and dispersive solid phase extraction (DSPE) was established for simultaneous determination of 7 pyrethroid insecticides (fenpropathrin, lambda-cyhalothrin, permethrin, cyfluthrin, cypermethrin, fenvalerate, deltamethrin) in fresh tea leaves. Samples were extracted ultrasonically with V(acetic acid):V(acetonitrile) =1:99, followed by the DSPE clean-up using primary secondary amine (PSA), octadecylsilane bonded silica (C18) and graphitized carbon black (GCB) as adsorbents. The sample extracts were determined by GC-ECD with matrix-matched external standard method. It was shown that good linearity was obtained at concentrations of 0.004-2 mg/L with correlation coefficients higher than 0.999 for these pyrethroids. The average recoveries of the 7 pesticides in fresh tea leaves were in the range of 80% to 101% at spiked levels of 0.01-0.5 mg/kg, with intra-day relative standard deviations lower than 8.4% (n=6) and inter-day relative standard deviations lower than 9.3% (n=3). The limits of detection and quantification were 0.002-0.02 mg/kg and 0.01-0.05 mg/kg, respectively. The method was simple, accurate, solvent saving. It was shown to be a suitable MRM method for determination of pyrethroid residues in fresh tea leaves.