Combination of microwave-assisted extraction and ultrasonic-assisted dispersive liquid-liquid microextraction for separation and enrichment of pyrethroids residues in Litchi fruit prior to HPLC determination.

A novel method for simultaneous determination of pyrethroids residues in Litchi fruit has been developed by HPLC-UV detection using microwave-assisted extraction (MAE) coupled with ultrasonic-assisted dispersive liquid-liquid microextraction (UADLLME). Extraction conditions of MAE and UADLLME were respectively investigated by single-factor experiments and response surface methodology. Optimized experimental conditions included 310μL of chlorobenzene as extraction solvent, 1.3mL of ethanol as dispersive solvent and 3min of extraction time for UADLLME. In the case of MAE, extraction temperature of 70°C, extraction time of 4min and solvent-to-materials ratio of 40:1 were adopted. Results demonstrated that the proposed method had good performance with linearity of 0.0050-4.98mg/L, recovery of 83.3-91.5%, RSDs below 5.6% and detection limit (LOD) of 1.15-2.46μg/L for six pyrethroids, offering higher extraction efficiency and larger enrichment factor. MAE-UADLLME provided a sensitive and efficient alternative to determination of trace amounts of pesticides residues in food samples.