Determination of sulfadimethoxine in milk with aptamer‐functionalized Fe3O4/graphene oxide as magnetic solid‐phase extraction adsorbent prior to HPLC

An aptamer (Apt) functionalized magnetic material was prepared by covalently link Apt to Fe₃O₄/graphene oxide (Fe₃O₄/GO) composite by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide hydrochloride and N‐hydroxysuccinimide, and then characterized by FTIR spectroscopy, X‐ray diffraction, and vibration sample magnetometry. The obtained composite of Fe₃O₄/GO/Apt was employed as magnetic solid‐phase extraction adsorbent for the selective preconcentration of sulfadimethoxine prior to analysis by high‐performance liquid chromatography. Under the optimal conditions (sample pH of 4.0, sorbent dosage of 20 mg, extraction time of 3 h, and methanol‐5% acetic acid solution as eluent), a good linear relationship was obtained between the peak area and concentration of sulfadimethoxine in the range of 5.0 to 1500.0 µg/L with correlation coefficient of 0.9997. The limit of detection (S/N = 3) was 3.3 µg/L. The developed method was successfully applied to the analysis of sulfadimethoxine in milk with recoveries in the range of 75.9‐92.3% and relative standard deviations less than 8.1%. The adsorption mechanism of Fe₃O₄/GO/Apt toward sulfadimethoxine was studied through the adsorption kinetics and adsorption isotherms, and the results show that the adsorption process fits well with the pseudo‐second‐order kinetic model and the adsorbate on Fe₃O₄/GO/Apt is multilayer and heterogeneous.