In this research, we have introduced the synthesis, characterization and application of lysine-modified Fe3O4/carbon dots (Fe3O4/CDs/Lys) nanocomposite as a new adsorbent in magnetic solid-phase extraction. The nanocomposite was synthesized by a simple method, and the characteristics of Fe3O4/CDs/Lys nanocomposite were evaluated by vibrating sample magnetometer, X-ray diffraction, transmission electron microscopy and Fourier-transform infrared spectroscopy. The nanocomposite was applied in the preconcentration and determination of codeine phosphate (COP) in blood serum sample via spectrofluorometric method. Fe3O4/CDs/Lys nanocomposite possessed high potential for the removal of COP, which might be related to the presence of more amine groups on the surface of nanocomposite due to Lys. Factors influencing the efficiency of COP extraction (i.e., contact time, pH, nanocomposite dosage, volume and type of desorbing solvent and desorbing time) were optimized. Using this method, COP was determined in the concentration range of 3.0–120.0 ng mL−1 with a detection limit of 1.2 ng mL−1. Real sample analysis results indicated that this method could be considered as a powerful tool for COP determination.
