A ferrofluidic hydrophobic deep eutectic solvent for the extraction of doxycycline from urine, blood plasma and milk samples prior to its determination by high-performance liquid chromatography-ultraviolet

The ferrofluid phase was prepared according to mixing magnetic nanoparticle and the hydrophobic deep eutectic solvent as a green microextraction solvent. This new composite was applied for vortex-assisted dispersive liquid–liquid microextraction (VA-HDES-ferrofluid-DLLME) of doxycycline (DOC) residual extraction and determined through high-performance liquid chromatography-ultraviolet (HPLC-UV). The characterization of magnetic nanoparticle was investigated by XRD, TEM and FESEM. The dependency of DOC microextraction to main variables and their interaction and find optimum points were undertaken using response surface methodology with either central composite design (CCD). Thus, the optimum pH, ionic strength, ferrofluid volume and vortex time for DOC extraction are determined to be 3.0, 4%w/v, 150 μL and 7 min, respectively. According to this condition, linear response is found to be greater than 10–400 ng mL−1, with a correlation coefficient of 0.983. The detection and quantification limits are 3.6 and 8.5 ng mL−1, while the repeatability and reproducibility as precision criteria (RSD%) are 3.74% and 4.15%, respectively. The DOC recoveries in all of the urine, blood plasma and milk samples are between 86.70 and 97.48%, with RSD% lower than 5.72%.