Comparison of size-selective techniques for the fractionation of magnetic fluids

Abstract Nanoparticles in magnetic fluids commonly display a broad distribution of magnetic and nonmagnetic parameters such as particle size. Nevertheless, magnetic fluids are used in many fields of application like material separation and biomedicine. Thereby, it is often the case that only a small number of particles contribute to the desired magnetic effect. Two fractionation methods, which separate according to the particle size, were tested in order to optimize magnetic fluids for applications. On the one hand, flow field-flow fractionation was used with an online multi-angle laser light-scattering detector that measures the particle size independently. For comparison, on the other hand, well-known size-exclusion chromatography was performed. The fractions obtained by both methods were magnetically characterized by magnetorelaxometry, a biomedical application of magnetic nanoparticles. The fractionations yielded are similar, independent of the method used. In this respect, flow field-flow fractionation has several advantages over size-exclusion chromatography in analytical use. Thus, flow field-flow fractionation requires neither the addition of electrolytes nor column materials. The fractions obtained display distinctly different magnetic properties compared to the original sample and are therefore especially suited for applications like magnetorelaxometry.