Fatty Acid–Based pH‐Switchable Deep Eutectic Solvents for the Extraction and Preconcentration of Chlorobenzenes From Water Samples Followed by Gas Chromatography–Electron Capture Detection

ABSTRACT An easy, safe, simple, and efficient pH‐switchable hydrophobic deep eutectic solvent (DES)‐based liquid‐phase microextraction was developed for the extraction of chlorobenzenes (CBs) from water samples followed by a gas chromatography–electron capture detector (GC–ECD). The switchability of the synthesized DESs was tested by changing the pH. The DES synthesized from thymol:octanoic acid (OA) in a molar ratio of 2:1 had the highest efficiency in extracting CBs from water samples. 1,4‐Dibromobenzene was used as internal standard (IS). The optimal conditions were established to be 20.0 µL of thymol:OA (2:1), 100 µL of 5 mol L −1 KOH, 100 µL of 5 mol L −1 HCl, 60 s of extraction time, and without salt addition. Under the optimum conditions, the calibration graphs were linear in the range of 0.005–150 µg L −1 , and limits of detection were in the range of 0.001–0.03 µg L −1 . The relative standard deviations, including intraday and inter‐day for 5.0 µg L −1 of dichlorobenzene isomers, 2.0 µg L −1 of trichlorobenzene and tetrachlorobenzene isomers, and 0.50 µg L −1 of pentachlorobenzene and hexachlorobenzene isomers in water with using IS, were in the range of 0.6%–3.2% ( n = 7) and 3.8%–6.7% ( n = 7), respectively. The accuracies, including inter‐day and intraday, were in the range of 93.5%–106.3% and 91.7%–109.4%, respectively.