In matrix formation of deep eutectic solvent used in liquid phase extraction coupled with solidification of organic droplets dispersive liquid-liquid microextraction; application in determination of some pesticides in milk samples.

In this work, a liquid-phase extraction procedure and dispersive liquid-liquid microextraction method based on deep eutectic solvents were combined and used for the simultaneous extraction of different classes of pesticides; including carbaryl, hexythiazox, pretilachlor, iprodione, famoxadone, sethoxydim and fenazaquin from milk samples. In the first step, a deep eutectic solvent was synthesized in milk sample and simultaneously, was used for extraction of the analytes along with precipitation of milk proteins. To assist the formation of the deep eutectic solvent and increasing the mass transfer rate of the analytes, ultrasonic irradiations was used. In the second step, the collected organic phase from pervious step was mixed (as dispersive solvent) with a water-immiscible deep eutectic solvent (ChCl: decanoic acid) and injected into deionized water. The cloudy solution was placed into an ice bath and the extraction solvent was solidified on the top of the solution. After removing the solid phase by a spatula, it was melted at room temperature and 1 μL of the extraction solvent was injected into the separation system. Under the optimum extraction conditions, low limits of detection and quantification within the ranges of 0.90-3.9 and 3.1-13 ng mL-1 were achieved, respectively. Precision of the method expressed as relative standard deviation was in the ranges of 3.8-5.3 and 4.8-6.9 for intra- and inter-day (n = 5) precision, respectively, at a concentration of 50 ng mL-1 of each analyte. Extraction recoveries and enrichment factors were between 64 and 89% and 320 and 445, respectively. Lastly, several milk samples were successfully analyzed using the proposed method.