Abstract: A novel and fast method for determination of pyrethroid pesticide residues in tea samples was established. The samples from the market were ultrasonic extracted by methanol before analysis with stir bar sorptive extraction-thermal desorption system-gas chromatography-mass spectrometry (SBSE-TDS-GC-MS). Polydimethylsioxane (PDMS) was used as extraction phase. The effects of extraction time, methanol addition and salting out on extraction efficiency were studied. The optimized conditions consist of a 10% methanol addition extracted with stir bars at 1100 r/min during 1h at ambient temperature. Desorption was carried out at 300℃ during 4 min under a helium flow of 50 ml/min in the splitless mode while maintained a cryoforming temperature of 0℃ in the programmed-temperature vaporization (PTV) injector of the GC-MS system. Under these described conditions, the detection limits of pyrethroid pesticides in tea sample are in the range of 2.36～12.60 ng/kg, and recoveries of the method are in the range of 91.50%～116.58%. The correlation coefficient of pyrethroid pesticides in tea samples is ≥ 0.9961. And the repeatability (n=6) of the method is less than 11% relative standard deviation (RSD). Pyrethroid pesticide residues in real life samples (red tea and oolong) can be determined rapidly by this method.

Key words: stir bar sorptive extraction, thermal desorption, pyrethroid pesticides, gas chromatography-mass spectrometry, tea