Determination of Pirimicarb Residues in Tobacco Leaves by High Performance Liquid Chromatography with QuEChERS Purification and Precolumn Derivatization

The sample of homogenized tobacco leaf (10.00 g) was taken, 10 mL of acetonitrile solution containing 1% (φ) acetic acid and 2-3 g of sodium chloride were added, and the mixture was extracted for 10 min by shaking. After centrifugation, 5 mL of the supernatant was taken, and put into a centrifuge tube pre-filled with 200 mg of PSA and 900 mg of MgSO₄. After vortex and centrifugation, 2.0 mL of the supernatant was taken, and blow to nearly dryness at 35℃ by nitrogen. The residue was dissolved by vortex in 500 μL of acidified aqueous solution (pH 3), 250 μL of OPA/2-mercaptoethanol solution and 250 μL of 0.05 mol·L^-1 sodium hydroxide solution, which was filtered into the injection vial though 0.2 μm microporous membrane. The solution was made its volume up to 1 mL with acidified aqueous solution (pH 3), and heated at 80℃ for 30 min for derivatization without light. The obtained solution was separated on EXTEND-C₁₈ column as the stationary phase and a mixture of methanol, acetonitrile and water with different volume ratios as the mobile phase for gradient elution, and pirimicarb was determined by high performance liquid chromatography (HPLC) with fluorescence detector. As shown by the results, the linear range of the standard curve of pirimicarb was 0.01-1.00 mg·L^-1, with detection limit (3S/N) of 0.01 mg·kg^-1. Test for recovery was made by standard addition method, giving results in the range of 84.4%-85.5%, with RSDs (n=6) of the determined values in the range of 1.4%-2.4%. This method was applied to the analysis of 30 tobacco leaf samples, the detection rate was 20% and the maximum detection amount was 0.06 mg·kg^-1.