GC Determination of 30 Organochlorine and Pyrethrin Pesticides in Tea with Clean-up by Gel Permeation Chromatography

The tea sample (1.00 g) was moistened with 5 mL of water and extracted with 50 mL of acetonitrile by rotating homogenization for 3 min. The mixture was filtered into a cylinder containing 2 g of solid NaCl. The supernatant (20.0 mL) was taken and evaporated to near dryness at 45 ℃. The residue was taken up with 10.0 mL of mixed solvent ethyl acetate and cyclohexane(1+1). The solution was then purified by GPC with the same mixed solvent as mobile phase at a flow-rate of 4.7 mL·min-1. Eluate flowed out during the interval 9-20 min was collected and evaporated to near dryness at 45 ℃. The residue was taken up with 5.0 mL of n-hexane and used for GC analysis using the Rxi-5MS quartz capillary column for separation and ECD for detection. Linearity ranges of the pesticides were kept in the same range of 0.02 - 0.50 mg·L-1, with detection limits (3S/N) ranged from 1×10-4 to 2×10-3mg·kg-1. Results of recovery and RSD′s (n=5) were found in the ranges of 83.2%-114.6% and 0.9%-4.8% respectively.