GC Determination of Residual Amounts of Organophosphorus Pesticides in Tobacco

Five organophosphorus pesticides as residues remained in tobacco were determined by gas chromatography with pulse flame photometric detector (PFPD).The powdered tobacco sample,after dehydration,was extracted with acetonitrile ultrasonically for 1 h,and the extract was evaporated to near dryness with a rotary evaporator.The residue was taken up with ethyl acetate,cyclohexane and a mixture of NaCl and anhydrous Na2SO4 (mixed in the ratio of 1 to 1 by mass).The supernatant was taken and purified by gel permeation chromatography with a mixture of cyclohexane and ethyl acetate (mixed in the ratio of 1 to 1 by vol.) as mobile phase for elution.The eluate was collected,concentrated to 1 mL and diluted to 5.0 mL with ethyl acetate.One μL of the solution was taken for GC analysis.HP-5 elastic quartz capillary column was used for separation,and method of external standard was adopted in the determination.Detection limits (3S/N) for the 5 pesticides were in the range from 0.02 to 0.04 mg·L-1.Recovery and precision were tested and results of recovery obtained were in the range of 81.4% to 99.8%,with values of RSD′s (n=6) ranged from 3.27% to 8.42%.