Application of hydrophobic deep eutectic solvent as the carrier for ferrofluid: A novel strategy for pre-concentration and determination of mefenamic acid in human urine samples by high performance liquid chromatography under experimental design optimization

In this study, ferrofluid of magnetic nanoparticles, oleic acid (OA), combined with hydrophobic deep eutectic solvent (Fe3O4 [iron oxide]-OA-DES) was prepared and coupled with vortex-assisted liquid phase microextraction, to pre-concentrate and determine mefenamic acid (MFA) in urine samples, following high performance liquid chromatography (HPLC). With regard to Fe3O4 nanoparticles, all sorbents were identified by SEM, TEM, and XRD. In addition, the influence of different parameters such as pH, ferrofluid volume, ionic strong (NaCl concentration %), and vortex time was investigated and optimized by response surface methodology (RSM) and central composite design (CCD). Maximum MFA extraction predicted by RSM (97.66) was achieved at pH 4.0, 60 μL of ferrofluid, 3%w/v NaCl, and 7 min vortex time with desirability of 1.0. Under the optimized conditions, the limits of detection (LOD) and the limit of quantification (LOQ) were 1.351 ng mL−1 and 4.575 ng mL−1, respectively. The intra-day and inter-day precision (RSD [relative standard deviation]%) in the concentrations of 50, 300, and 700 ng mL−1 of MFA were less than 3.6% and 4.2%, respectively. The method developed in our study could successfully determine MFA in urine samples. The MFA microextraction in urine samples were between 80.25 and 97.44% with RSD% less than 4.60%. Inclusion of ferrofluid in a miniaturized method for sample preparation is proportional to the achievement of high microextraction percentage using green analytical method.