Development of a simple and efficient pretreatment technique named salt– and pH–induced solidified floating organic droplets homogeneous liquid–liquid microextraction

Pyrethroid compounds are a new generation of insecticides which are widely used to control pests in agricultural activities. These compounds are the forth main group of the most used insecticides after organophosphates, organochlorines and carbamates [1, 2]. However, they could give rise to serious risks for the health and safety of the consumers of the agricultural products due to their distribution on large areas of agricultural land. In this study, a new approach named salt–and pH–induced solidified floating organic droplets homogeneous liquid–liquid microextraction has been developed in a home–made extraction device for the extraction and preconcentration of some pyrethroid insecticides from various fruit juice samples prior to gas chromatography–mass spectrometry determination. In the present work, two parallel glass tubes with different lengths and diameters were connected with a stopcock and used as an extraction device. Firstly, an acidic organic solvent with low solubility in water (pivalic acid) as an extraction solvent was mixed with an alkaline aqueous phase containing the analytes and a homogenous solution was obtained. This solution was filled into the wide side of the extraction device. The other side (narrow and long tube) was filled with a hydrochloric acid solution. Then, the stopcock was opened and the hydrochloric acid solution was flowed into the other tube containing the homogenous solution under hydrodynamic pressure. By this action, an acid–base reaction was occurred, so the homogenous solution was broken and the target analytes were extracted into the produced fine droplets of the organic solvent. By passing the produced droplets of the extraction solvent through the solution, the analytes were extracted and the organic phase was collected on the surface of the aqueous phase. Afterward the device was placed into an ice bath and the solidified droplets were used for analysis. Under the optimum conditions, limits of detection and quantification were obtained in the ranges of 0.006–0.038, and 0.023–0.134 ng mL–1, respectively. The extraction recoveries and enrichment factors of the selected analytes ranged from 365–460 and 73–92%, respectively. The relative standard deviations were lower than 9% for intra– (n=6) and inter–day (n=4) precisions at a concentration of 2 ng mL–1 of each analyte. Finally, some fruit juice samples were effectively analyzed by the proposed method.