Vincristine has a wide spectrum of clinical activity and is currently used in the treatment of leukemia. Despite its high therapeutic properties, vincristine has common side effects. Accordingly, it is desirable to determine vincristine in plasma for the use of the drug with strict monitoring. In the present research, for the first time a hydrophobic deep eutectic solvent (DES) composed of methyltrioctylammonium chloride (MTOAC) and n-butanol in a molar ratio of 1 : 3 was used as the extractant in dispersive liquid–liquid microextraction (DLLME) for the extraction and determination of vincristine in the plasma of children with leukemia prior to its analysis by high-performance liquid chromatography-ultraviolet detection (HPLC-UV). Under optimal experimental conditions, the method showed good linearity with a correlation coefficient (R2) of 0.9986 in the linear range of 0.06–300 μg L−1, low limit of detection of 0.02 μg L−1 and acceptable extraction efficiency (EE) of 88.4%. In the final stage of the study, this proposed technique was successfully applied to determine vincristine in real plasma, and the obtained results demonstrated the ability of the synthesized DES to extract drugs from biological fluids.
