A novel method for chemically synthesizing Prussian blue (PB) magnetic nanoparticles was developed. Firstly magnetic Fe₃O₄ granule was obtained by the reaction between FeSO₄ and FeCl₃ under 80 ℃, then such Fe₃O₄ granule was reacted with K₃Fe(CN)₆ in acidic solution (pH～2) to form magnetic PB nanoparticles. The magnetic properties of magnetic PB nanoparticles were studied. Chemically modified electrode based on magnetic PB nanoparticles attached on the surface of solid paraffin carbon paste electrode was prepared. Hydrogen peroxide and hydrazine hydrate were detected by this electrode. There was a linear relationship between the reductive peak height and the concentration of hydrogen peroxide in the concentration range of 2×10^－6～5×10^－3 mol/L, while the linear relation between the oxidation currents and the concentration of hydrazine hydrate was in the range of 7.2×10^－7～3.6×10^－4 mol/L. The modified electrode based on magnetic powder was renewable with the virtue of good electrocatalytic property.

Key words: magnetic nanoparticle, chemically modified electrode, Prussian blue, hydrogen peroxide, hydrazine hydrate