GC Determination of Residual Amount of Methamidophos in Tea with Solid Phase Extraction

Sample of tea was extracted with ethyl acetate, and the supernatant was taken and evaporated to near dryness at 50 ℃. The residue was dissolved with ethyl acetate, and purified by passing through a column packed with silica gel and graphitized carbon. The column was washed with ethyl acetate to remove impurities, and then eluted the analyte with alkalified acetonitrile. The eluate obtained was evaporated to near dryness at 50 ℃, and taken up with 1 mL of ethyl acetate and used for GC analysis using the DB-1701 chromatographic column for separation and FPD for detection. Linearity range of methamidophos was kept between 0.010-1.00 mg·L-1, with detection limit (3S/N) of 0.005 mg·kg-1. Tests for recovery and precision were made by addition of 0.010, 0.020, 0.080 mg·kg-1 of standard solution, and analyzed by the proposed method, giving values of recovery in the range of 85.0%-90.9% and values of RSD′s (n=6) in the range of 2.2%-4.3% respectively.