Extraction of diclofenac by SiO₂ -NH₂ @Fe₃ O₄ and its determination: Central composite design

In this work, magnetic nanoparticles (Fe₃ O₄ ) were prepared by simple co-precipitation method in aqueous medium and then subsequently modified with tetraethyl orthosilicate and 3-aminopropyl triethylenesilane. The properties of the particles were characterized by FTIR spectroscopy X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The SiO₂ -NH₂ @Fe₃ O₄ particles were successfully applied to simultaneously enrich and separate diclofenac from water, urine, and plasma samples. The method, which takes the advantages of both nanoparticle adsorption and magnetic phase separation from the sample solution, could avoid some of the time-consuming experimental procedures related to the traditional solid phase extraction. The main parameters affecting extraction and desorption efficiency such as pH, amount of SiO₂ -NH₂ @Fe₃ O₄ , volume of desorption solvent, and extraction time were screened. The significant variables were optimized by using central composite design. At optimum conditions values of variables set as pH = 4, 10 mg SiO₂ -NH₂ @Fe₃ O₄ , 0.5 mL methanol, and 15 min extraction time and then the extracted diclofenac were injected to HPLC for analysis. The linear response (r²  > 0.9992) was obtained in the range of 0.004-15 µg/mL with detection limit 0.0012 µg/mL and extraction recovery was in the range of 92-96% with RSD < 5% (n = 6).