In order to develop a more simple and efficient procedure of preconcentration and determination of the organic pollutants in waters it has been proposed to apply a static mode of magnetic solid-phase extraction using a novel surface-modified nanosized sorbent. The synthesis procedure of the sorbent consisted of: 1) synthesis of magnetite nanoparticles by co-precipitation method; 2) subsequent surface modification with tetraethoxysilane ( TEOS ) and cetyltrimethylammonium bromide ( CTAB ). Both stages were performed using microwave heating. The formation of nanoparticles was confirmed by SEM and dynamic light scattering method. The possible structure of the surface adsorption layer of the sorbent particles was characterized by comparing experimental and literature data on the CTAB adsorption. Sorption properties of the material have been investigated using 4-nonylphenol (4-NF) as an example. The extraction of 4-NF from aqueous solutions and surface waters with typical salt and dissolved organic matter content was shown to be quantitative. The technique based on the magnetic solid-phase extraction and HPLC determination of 4-NF has been developed. The duration of a single analysis was about 35-40 min, detection limit – 2 µg/L of 4-NF. Keywords: magnetic nanoparticles, microwave synthesis, magnetic separation, 4-nonylphenol, HPLC, natural waters (Russian) DOI: http://dx.doi.org/10.15826/analitika.2015.19.3.006 D.V. Pryazhnikov, M.S. Kiseleva, I.V. Kubrakova V.I. Vernadsky Institute of Geochemistry and Anaytical Chemistry, Russian Academy of Sciences, Moscow, Russian Federation