Magnetic fractionation of magnetic fluids

The propel ties of magnetic nanoparticles in magnetic fluids often exhibit a broad distribution, so in many applications only a small number of particles contribute to the desired magnetic effect.. In order to optimize magnetic fluids for applications, preference is given to methods that separate the nanoparticles on the basis of their magnetic properties. Therefore, a magnetic method has been developed for the fractionation of magnetic fluids into two or more fractions. A common magnetic fluid was fractionated by this method. Magnetic and nonmagnetic properties of the fractions obtained and the original sample were measured. In addition to measurement of their magnetization curves they were also investigated by magnetic resonance and magnetorelaxometry, two biomedical applications of magnetic nanoparticles. The influence of the ion concentration of the washing solutions on the magnetic fractionation was additionally tested. The magnetic fractions have distinctly better magnetic properties than the original samples and are therefore especially suited for applications. Furthermore, the results indicate that the magnetic method fractionates the particles in accordance with their magnetic moment and that it has good recovery as well as reproducibility. Finally, magnetic fractionation is compared with other fractionation techniques. (C) 2000 Elsevier Science B.V. All rights reserved.