Magnetic solid-phase extraction based on methylcellulose coated-Fe3O4–SiO2–phenyl for HPLC–DAD analysis of sildenafil and its metabolite in biological samples

In the present study, magnetic nanoparticles (MNPs) with phenyl functionalized core and a hydrophilic methylcellulose coating were synthesized. The functionalized MNPs showed excellent dispersibility in aqueous solution and they were applied to magnetic solid phase extraction (MSPE) of sildenafil and its metabolite, desmethyl sildenafil, from human urine and plasma samples followed by high performance liquid chromatographic analysis. The factors that may influence the extraction, including the amount of MNPs, pH and salt concentration of sample solution, extraction and desorption time, and the volume of desorption solvent, were investigated in detail. Under the optimum MSPE conditions, the developed method showed satisfactory reproducibility with intra-day and inter-day relative standard deviations less than 8.2% and low limits of detection of 0.41–0.96 ng mL−1 from urine and plasma samples. The proposed material possessed good water compatibility and demonstrated excellent applicability for biological samples.