Dispersive liquid-liquid microextraction based on the solidification of a floating organic droplet followed by gas chromatography for the determination of five pyrethroid pesticides residues in liquid milk samples

A novel dispersive liquid-liquid microextraction based on solidification of floating organic droplet method (DLLME-SFO) combined with gas chromatography coupled with ECD detector was developed for the determination of five pyrethroid pesticides (fenpropathrin, cyhalothrin, cyfluthrin, fenvalerate, deltamethrin) in liquid milk. The following procedure was used for the sample pretratment:25 μL hexadecane (extraction solvent), 600 μL acetone(dispersive solvent), and NaCl (6 wt%) were added, followed by vortex oscillation extraction time 3 min. Then centrifugal for 3 min at -5℃ and 10 000 r/min, and dislodge water phase. After thawed, the sample was analysis by gas chromatography. Good linearity was obtained at concentrations from 5.00 to 250 μg/kg with correlation coefficients higher than 0.999 0 for these pyrethroids. The average recoveries of the 5 pesticides in liquid milk were in the range between 90% and 104% at spiked levels of 5 to 20 μg/kg, with intra-day relative standard deviations lower than 5.9% (n=6) and inter-day relative standard deviations lower than 7.8% (n=3). The limits of detection and quantification were 0.75-2.17 μg/kg and 2.52-7.22 μg/kg, respectively. This new method is simple, solvent saving, accurate, reliable and applicable for the analysis of pyrethroid pesticides in liquid milk samples.