Extraction of trace amounts of cadmium in fish and mollusk by Fe3O4@N-carbon quantum dots as adsorbent

The extraction of trace amounts of cadmium ions in fish and mollusk was investigated using magnetic N-doped carbon quantum dots as adsorbent. The characterization of the adsorbent was performed using Fourier transform infrared spectroscopy, UV–Vis spectroscopy, X-ray diffraction spectrometry, vibrating sample magnetometer and transmission electron microscopy. Important parameters, with effective role on extraction process were optimized in three levels by central composite design. The parameters including extraction time (5, 35, 65 min), amount of the magnetic sorbent (10, 30, 50 mg) and pH (3, 5, 7) were recognized as the major factors in adsorption process and optimized. The variables including type (HCl, HNO3, HCl/thiourea, HNO3/thiourea), volume (1, 3, 5 mL) and concentration of desorption solvent (0.01, 0.5, 1 mol L−1), and desorption time (1, 5.5, 10 min) were optimized in desorption process. Under the optimum conditions (pH of 6.30; extraction time of 5 min; adsorbent amount of 10 mg; desorption solvent volume of 1.5 mL; desorption time of 5 min; desorption solvent concentration of 0.5 mol L−1), the adsorption capacity was 246 mg g−1. The detection (S/N = 3) and quantitation limits of the method were found to be 0.06 and 0.2 μg L−1, respectively. The method was also successfully used for the determination of Cd2+ in fish and mollusk samples with satisfactory recoveries (≥ 97.4%).