Homogeneous liquid-liquid extraction performed in narrow tube followed by in-syringe dispersive liquid-liquid microextraction based on deep eutectic solvents; Application in extraction and preconcentration of some herbicides from tea

In recent years, deep eutectic solvents (DESs) engrossed more attentions in analytical chemistry [1]. DESs generally are formed from two compounds which they are hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA). By mixing HBD and HBA, hydrogen bonding interaction is occurred and a mixture with low melting point (near to room temperature) is prepared [2]. These solvents are considered as a suitable replacement for traditional extraction solvent due to their low toxicity, high biodegradability, and extraction capability. Simple preparation of DESs and availability of different compounds in synthesis of them expand their use as solvents in many fields. Sample preparation methods are one of the main fields which are involved with DESs [3]. The usage of DESs as acceptor phases in extraction methods attracts more attentions in the recent years. A homogeneous liquid-liquid extraction performed in narrow tube coupled to in-syringe dispersive liquid-liquid microextraction based on deep eutectic solvent has been developed for the extraction of some herbicides from tea samples. The deep eutectic solvent used in homogeneous liquid-liquid extraction is a water-miscible solvent which is used as a dispersive solvent in the next step. In this method, firstly, sodium chloride as a separation agent is filled into the narrow tube and the tea sample is placed on top of the salt. Then a mixture of deionized water and deep eutectic solvent is passed through the tube. In this procedure, the deep eutectic solvent (ChCl: phenol) is realized as tiny droplets in contact with salt. They go up through the tube and collected on top of the remained solution. By passing the droplets from the tea layer placed on the salt layer, the analytes are extracted into them. After collecting the solvent as separated layer, it is removed and mixed with another deep eutectic solvent (ChCl: butyric acid) and the mixture is dispersed into deionized water placed in a syringe. After adding acetonitrile to break up the cloudy state, the collected organic phase is injected into gas chromatography-mass spectrometry. Under optimal conditions, low limits of detection and quantification in the ranges of 2.6-8.4 and 9.7-29 ng kg-1, respectively, were obtained. Relative standard deviations lower than 7% express an acceptable repeatability for the present method. The extraction recoveries and enrichment factors in the ranges of 70-89% and 350-445 were obtained, respectively.