Determination of Pestiside Multi-Residues in Onion，Leek and Ginger by Dispersive Solid-Phase Extraction and GC/MS

A multi-residue analytical method was developed for the determination of 28 pesticide residues in onion，leek and ginger using gas chromatography-mass spectrometry（GC/MS）. The samples were treated with microwave (500 W，90 s) before being crushed to make the allinase inactive and to eliminate the matrix effect. The pesticide residues were extracted from samples by acetonitrile, primary secondary amine (PSA) and C₁₈ mixed adsorbents， which were used for purification at the same time to achieve quick， easy， cheap， effective， rugged and safe analysis. Internal standard substance-triphenyl phosphate (TPP) was used to overcome matrix effect and achieve quantitatively determination. The correlation coefficients are geater than 0.995， and the limits of the detection are in the range of 0.1－20.8 μg/kg. The method is validated at two fortification levels of 0.05 mg/kg and 0.1 mg/kg in blank samples, phorate, omethoate and cyfluthrin cannot be quantitatively determined in ginger due to interference. The averge recoveries are in the range of 70%－130% excepted for methmidopos， acephate and chlorothalonil that below 70%. The relative standard deviations(RSDs) are in the range of 0.5%－20%.