Herein, at first, a magnetite@MIL-53(Fe)-NH2 core-shell nanocomposite was fabricated and then modified via postsynthetic modification by dithiocarbamate moieties to obtain a magnetite@MIL-53(Fe)-NH-CS2 nano-adsorbent. The constructed material was used for extraction/separation of ultra-trace Hg (II) from seawater, river water, and fish samples, and then the enriched mercury was quantified by CVAAS instrument. Characterization of magnetite@MIL-53(Fe)-NH-CS2 nano-adsorbent was carried out by scanning electron microscopy, X-ray diffraction analysis, CHNS analysis, FT-IR spectroscopy, and magnetometry. Optimization of the affecting variables was conducted via the design of experiment methodology. After that, adsorption isotherms and kinetic studies were carried out. The experimental data were well fitted to the Langmuir and pseudo second-order kinetic models for adsorption study and kinetic study, respectively. Accordingly, a maximum adsorption capacity and a Langmuir constant (KL) of 250 mg g1 and 0.102 L mg1 were obtained, respectively. The LOD and linearity of the preconcentration method were 0.006 ng ml1 and 0.02–50 ng ml1 (r 2 = 0.9945), respectively. A very high preconcentration factor equal to 300 was attained after optimization. The accuracy of the current method was proved by analyzing IAEA-436 (Tuna fish flesh homogenate, AQCS) certified reference material. Finally, the current extraction/separation method was employed to the extraction and quantification of ultra-trace amounts of mercury ions in seawater, river water, and fish samples. K
