Graphene-Fe₃ O₄ as a magnetic solid-phase extraction sorbent coupled to capillary electrophoresis for the determination of sulfonamides in milk

Graphene-Fe₃ O₄ nanoparticles were prepared using one-step solvothermal method and characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy, and vibrating sample magnetometry. The results demonstrated that Fe₃ O₄ nanoparticles were homogeneously anchored on graphene nanosheets. The as-synthesized graphene-Fe₃ O₄ nanoparticles were employed as sorbent for magnetic solid-phase extraction of sulfonamides in milk prior to capillary electrophoresis analysis. The optimal capillary electrophoresis conditions were as follows: 60 mmol/L Na₂ HPO₄ containing 2 mmol/L ethylenediaminetetraacetic acid disodium salt and 24% v/v methanol as running buffer, separation voltage of 14 kV, and detection wavelength of 270 nm. The parameters affecting extraction efficiency including desorption solution, the amount of graphene-Fe₃ O₄ nanoparticles, extraction time, and sample pH were investigated in detail. Under the optimal conditions, good linearity (5-200 μg/L) with correlation coefficients ≥0.9910 was obtained. The limits of detection were 0.89-2.31 μg/L. The relative standard deviations for intraday and interday analyses were 4.9-8.5 and 4.0-9.0%, respectively. The proposed method was successfully applied to the analysis of sulfonamides in milk samples with recoveries ranging from 62.7 to 104.8% and relative standard deviations less than 10.2%.