Application of a Deep Eutectic Solvent for Dispersive Liquid–Liquid Microextraction of Trace Amount of Pb (II) in Water Samples and Determination by Microvolume UV–Vis Spectrophotometry

There is an increasing interest in synthesizing/developing novel deep eutectic solvents (DESs) as green and/or sustainable solvents for various applications (e.g., analytical chemistry). In this study, a hydrophobic DES is reported for dispersive liquid–liquid microextraction (DLLME) of Pb (II) in water samples prior to its determination by UV–Vis spectrophotometry. A hydrophobic DES was prepared by mixing thymol as the donor of the hydrogen bond donor and benzyltriethylammonium chloride (BTEAC) as the acceptor of the hydrogen bond. The critical factors which affect the proposed method were studied and optimized. The experiments revealed that under the optimized conditions, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.23 ng mL⁻¹ and 0.8 ng mL⁻¹, respectively. Furthermore, the calibration curve showed a linear behavior in the range of 1.0–200 ng mL⁻¹ with R² = 0.9994. The precision (RSD values) at 2, 20, and 200 ng mL⁻¹ of Pb (II) was below 5.0% (n = 6). Finally, the developed procedure was applied to extract and determine trace levels of Pb (II) in various real water samples (recovery > 90%).