Abstract: In this study, an analytical method using homogeneous liquid-liquid microextraction based on the solidification of sedimentary ionic liquid coupled with high performance liquid chromatography (HPLC) was developed and applied to the simultaneous determination of five phenylurea pesticide residues in vegetables. The hydrophilic ionic liquid noctyltributylphosphonium bromide ([P4448]Br) was used as the microextraction solvent. The extraction was carried out with the aid of ultrasound, after centrifugation and cooling. The analytes were enriched into the ionic liquid phase and deposited at the bottom of the centrifuge tube. The ionic liquid phase was diluted and used for chromatographic analysis. The combined use of one-factor-at-a-time method and Box-Behnken design response surface methodology was proposed to optimize the important extraction conditions. The experimental results showed that the regression models for the target analytes were all significant (P > 0.05). Good linearity with correlation coefficients greater than 0.998 1 was obtained under the optimum conditions. The limits of detection (LODs) and limits of quantification (LOQs) were in the range of 2.19–5.35 and 7.30–17.82 μg/kg, respectively. The recoveries for spiked samples were between 82.84% and 117.49% with relative standard deviations (RSDs) lower than 9.93%. The present method has the advantages of less solvent consumption, environmental protection and simple operation and thus can be used for the extraction and detection of phenylurea pesticide residues in vegetables.

Key words: solidification of sedimentary ionic liquids, homogeneous liquid-liquid microextraction, phenylurea pesticides, response surface analysis, vegetables, high performance liquid chromatography