Magnetic solid phase extraction of mefenamic acid from biological samples based on the formation of mixed hemimicelle aggregates on Fe3O4 nanoparticles prior to its HPLC-UV detection

• The synthesis and application of CTAB coated magnetic nanoparticles sorbent are proposed.
• The sorbent was used for extraction/preconcentration of mefenamic acid coupled to HPLC-UV determination.
• A high preconcentration factor (98) was obtained.
• The method was applied to determination of mefenamic acid in biological fluids.

A novel and sensitive solid phase extraction method based on the adsorption of cetyltrimethylammonium bromide on the surface of Fe3O4 nanoparticles was developed for extraction and preconcentration of ultra-trace amounts of mefenamic acid in biological fluids. The remarkable properties of Fe3O4 nanoparticles including high surface area and strong magnetization were utilized in this SPE procedure so that a high enrichment factor (98) and satisfactory extraction recoveries (92–99%) were obtained using only 50 mg of magnetic adsorbent. Furthermore, a fast separation time (about 15 min) was achieved for a large sample volume (200 mL) avoiding time-consuming column-passing process of conventional SPE. A comprehensive study on the parameters effecting the extraction recovery such of the amount of surfactant, pH value, the amount of Fe3O4 nanoparticles, sample volume, desorption conditions and ionic strength were also presented. Under the optimum conditions, the method was linear in the 0.2–200 ng mL−1 range and good linearity (r2 > 0.9991) was obtained for all calibration curves. The limit of detection was 0.097 and 0.087 ng mL−1 in plasma and urine samples, respectively. The relative standard deviation (RSD %) for 10 and 50 ng mL−1 of the analyte (n = 5) were 1.6% and 2.1% in plasma and 1.2% and 1.9% in urine samples, respectively. Finally, the method was successfully applied to the extraction and preconcentration of mefenamic acid in human plasma and urine samples.