Superparamagnetic nanoparticles previously modified with mercaptopropyltriethoxysilane were employed in this work as electrode modifiers, for direct use in the presence of an external miniature magnet, for the analysis of mercury ions from aqueous solutions, as well as from crude oil. After capturing the mercury ions, the nanoparticles were magnetically concentrated at the electrode surface. The nanoparticies coating exhibited a sharp electrochemical response, and the preconcentration effect led to a strong enhancement of the electrochemical signals. The in situ magnetic coupled electroanalysis was successfully demonstrated for mercury ions and confronted with parallel energy dispersive X-ray fluorescence measurements. Rather consistent results were observed for mercury ions either from aqueous solutions, as well as from the crude oil samples. (C) 2011 Elsevier B.V. All rights reserved.