Abstract: A novel ultrasound-assisted dispersive liquid-liquid microextraction based on solidification of floating organic droplet method (UA-DLLME-SFO) which combined with gas chromatography coupled with ECD detector was developed for the determination of five pyrethroid pesticides (fenpropathrin, cyfluthrin, cyhalothrin, fenvalerate, deltamethrin) in tea. The optimal liquid-liquid microextraction experiment conditions were as follows: 20βμL hexadecane was used as extraction solvent. After ultrasound for 30 min under 35℃, 800βμL of acetone (disersive solvent) were rapidly transferred. The NaCl Mass Fraction was 4% and pH was adjusted to 4. The sample solution was then centrigugated at 10 000 r·min^-1 for 5 min under －3℃ and then injected for gas chromatography analysis. It was shown that a good linearity for these pyrethroids was obtained at concentrations of 1.0 to 150.0 μg·kg^-1 with correlation coefficients higher than 0.9994. The average recoveries of the 5 pesticides in liquid milk were in the range of 92.3% to 99.6% at spiked levels between 1 to 5 μg·kg^-1, with intra-day relative standard deviations lower than 3.5%（n=6）and inter-day relative standard deviations lower than 5.9% (n=3). The limits of detection and quantification were 0.11-0.24 μg·kg^-1 and 0.36-0.81 μg·kg^-1 , respectively. The proposed method is simple, fast, safe, reliable and applicable for analyzing pyrethroid pesticides in tea samples.

Key words: ultrasound-assisted, DLLME-SFO, gas chromatography, pyrethroid pesticides