Abstract–Adsorptive removal and preconcentration of Brilliant Green (BG) on Fe3O4 magnetic nanoparticles functionalized with cetyltrimethylamonium bromide (CTAB) was investigated in a batch system. The method was based on the analyte adsorption and direct determination by UV–visible spectrophotometry. Various experimental factors such as pH, adsorbent dose (m) and initial concentration (cd) were evaluated and optimized using Box-Behnken design through adsorption of BG on the modified adsorbent. The optimized conditions for maximum removal efficacy (99%) were: pH 9; amount of nanoparticles, 7.1 mg; CTAB, 5.4 mg and cd = 100 mg/L. Under optimum conditions, preconcentration of BG with enrichment factor of 35, LOD = 4 μg/L and RSD = 2.7% (n = 10) for 10 μg/L sample were achieved. The maximum monolayer adsorption of BG onto nano-Fe3O4‒CTAB through running Langmuir isotherm was obtained as 416 mg/g. The morphology and characteristics of the prepared nano-Fe3O4‒CTAB were investigated by scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectroscopy and thermogravimetric analysis
