A new three–components deep eutectic solvent as an extraction solvent in dispersive liquid–liquid microextraction

Pesticides are a main group of chemicals which are widely used in prevention or control of fruit diseases or weeds. In spite many positive effects of the application of pesticides in agriculture, most pesticides are harmful to environment and are known or suspected to be toxic to human. Their adverse effects on human health may include acute neurologic toxicity, chronic neurodevelopment impairment, and endocrine systems or cancer [1]. Thus, developing a fast, simple, sensitive, and reliable analytical method to monitor the residue of pesticides in the environment is of prime importance. Sample preparation is one of the most important steps in an analytical process. For the analysis of pesticide residues, several sample preparation methods have been developed such as liquid–liquid extraction [2] and solid–phase extraction [3] which have some drawbacks. In 2006, Assadi and co–workers introduced a novel liquid phase microextraction technique named dispersive liquid–liquid microextraction (DLLME) [4]. It was been proved to be a simple, low–cost, and fast method using the small amount of an extraction solvent and the low sample volume together with high enrichment factor for the analysis of different analytes [5]. In the present study a liquid–liquid extraction combined with a new three–components deep eutectic solvent (DES–DLLME) has been developed, for the extraction and preconcentration of ten pesticides from different aquaus samples. The DES was prepared by mixing dichloroacetic acid, menthol, and n–butanol at 0.5:0.5:1 molar ratio. The DES was mixed with methanol (as a disperser solvent) and the mixture was rapidly injected into an aqueous phase containing the analytes. The obtained cloudy solution was centrifuged and 1 µL of the sedimented phase was injected gas chromatography–flame ionization detector. The influence of several variables on the extraction efficiency were investigated and optimized. Under the optimal conditions, extraction recoveries were obtained in the range of 53–86% and the calibration curves were linear in wide ranges with a correlation coefficient ≥0.9985. Intra– (n = 6) and inter–day (n = 5) precisions of the method were satisfactory with relative standard deviations less than or equal to 7.0% (at two concentrations of 10 and 50 µg L−1, each analyte). Moreover, the detection limits and enrichment factors for the target analytes were obtained in the ranges of 0.11–0.23 µg L−1 and 1760–2853, respectively. Finally, the proposed method was applied on different samples including tea , rose water, lemon balm, mint, and pussy distillates.