Development of solidification of floating organic drops liquid–liquid microextraction in a newly designed extraction device

Abstract

A new approach to continuous homogeneous liquid–liquid microextraction based on the solidification of organic droplets has been developed in a newly designed home-made extraction device for the extraction and preconcentration of organothiophosphate pesticides from different fruit juices and vegetable samples prior to gas chromatography-mass spectrometry. In the present work, two parallel glass tubes with different lengths and diameters were connected together with a stopcock in which cool water was circulated from the wide side of them. This was used as the extraction device. Firstly, a homogeneous phase containing the sample solution and an extraction solvent (cyclohexanol) was filled into the wide diameter side of the device. Then sodium sulfate solution placed into the other side of the device was flowed into the homogeneous solution to release the extraction solvent from the solution. Along with the flowing of sodium sulfate, cool water was circulated from the wide side of the device. In this step, the extraction solvent was produced as tiny droplets in all parts of the solution and the analytes were extracted into the extraction solvent and the organic phase was solidified simultaneously. Afterward the solidified droplets were used for analysis. Under the optimum conditions, limits of detection and quantification were obtained in the ranges of 0.026–0.076, and 0.091–0.28 ng mL⁻¹, respectively. The extraction recoveries and enrichment factors of the selected pesticides in liquid samples ranged from 216–273 and 65–82%, respectively. The relative standard deviations were lower than 8% for intra (n = 6) and inter-day (n = 4) precisions at a concentration of 3 ng mL⁻¹ of each analyte. Finally, some vegetable and fruit samples were effectively analyzed using the proposed method.