Sequential extraction and enrichment of pesticide residues in Longan fruit by ultrasonic-assisted aqueous two-phase extraction linked to vortex-assisted dispersive liquid-liquid microextraction prior to high performance liquid chromatography analysis

Abstract

A simple, green and efficient method for extraction, purification and enrichment of pesticide residues of triazoles and pyrethroids in Longan fruit was developed by ultrasonic-assisted aqueous two-phase extraction (UAATPE) coupled to vortex-assisted dispersive liquid-liquid microextraction (VADLLME). Using an aqueous two-phase system (ATPS) of ethanol/K2HPO4 as extraction solvent, the composition of the ATPS, extraction temperature and time were investigated, respectively. Then VADLLME process also was optimized by investigating type and volume of extracting and dispersive solvents, vortex-assisted time and salt addition. The optimum conditions were as follows: the ATPS composition of ethanol concentration 30.0% (w/w) and K2HPO4 concentration 25% (w/w), extraction temperature 70 °C and extraction time 15 min for UAATPE; 1-dodecanol 200 μL as extraction solvent, ethanol 1.25 mL as dispersive solvent, vortex-assisted time 1.5 min and addition of NaCl 4% (w/v) for VADLLME. Ethanol as extraction solvent and dispersive solvent could directly connect UAATPE with VADLLME without extra steps. By means of HPLC-DAD detection, nine pesticides had good linearity ranged from 0.0200 to 13.59 μg/mL (R2 ≥ 0.9957). LODs and LOQs were in the range of 0.005576−0.01740 μg/mL and 0.01859−0.05010 μg/mL, respectively. UAATPE-VADLLME coupled to HPLC was successfully applied to simultaneous determination of multiple pesticides in Longan fruit, and mean recoveries and RSDs were between 76.95% and 98.63%, 1.2% and 9.8%, respectively. Furthermore, myclobutanil, fenpropathrin and deltamethrin were detected in pericarp and pulp of Longan samples from different districts, respectively.