In this research, a simple and rapid method for the separation and preconcentration of trace amounts of crystal violet (CV) from aqueous sample solutions by modified magnetic nano-particles (MNPs) has been developed. The modification of magnetite nanoparticles was conducted by tetra ethoxysilane (TEOS) followed by micelles of anionic surfactant (SDS) to enhance the preconcentration of CV. To characterize the shape and structure of the nanoadsorbent, FT-IR and XRD procedures were used. Also, the

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... average size of the synthesized nanoparticles was achieved between 30 and 40 nm by TEM technique. The effects of some important parameters such as: aqueous solution pH, adsorbent dosage, contact time, temperature and desorption conditions on the separation and concentration of CV were investigated. So, under optimal experimental conditions: aqueous solution pH 6, solution temperature = 20 °C, 7 mg of adsorbent, 1 mL of eluent (0.8 mL of acetonitrile + 0.2 mL of acetic acid), the recovery of CV from river water samples was achieved 98.32 ± 0.056% (n = 5) in two short periods of time for extraction (5 min) and elution (2 min). The maximum sorption capacity of the nano-composite was determined to be 16.37 mg/g. Also linear dynamic range and limit of detection were calculated to be 10-2500 ppb and 1.82 ppb, respectively. Finally, the proposed method was successfully applied for the separation and concentration of CV from the real water samples and the results were satisfied. Graphical abstract Under optimal conditions, a significant amount of nanocomposite was added to the dye solution. After dye removal in a short time, the nanoadsorbent-containing dye was magnetically separated from the solution and then the adsorbed dye was eluted into low volume of a suitable eluting solution.