Magnetic solid phase extraction particles (MSPE) were produced using magnetite nanoparticles with diameters between 9 and 13 nm as nucleating agent. The produced particles with magnetite cores were smaller, and more irregular and poly-dispersed, than those produced in the absence of the magnetite particles. The average diameters of the particles were 377 and 521 nm, respectively, for silica particles with and without magnetic core, whereas the diameters of the different grafted particles were of the same order of magnitude than the silica particles with magnetic cores. BET results indicated surface areas ranging between 9 and 37 m(2) g(-1) The TGA results showed that the particles contained about 10% water and other solvents, and between 5 to 6% grafted groups. The thermal decomposition of the particles (presented under Supplementary Information) was autocatalytic with activation energies of 367, 546, and 616 kJ mol(-1) for particles grafted with cyanopropyl (cyano), octyl, and trimethyl (TMS), respectively. The order of dispersity of the particles in water followed the sequence cyano > PMA > TMS >> octyl, whereas the pesticides removing efficiency followed the reverse order.