 Unlike conventional methods that measure the susceptibility of superparamagnetic materials, a MIA-based on non-linear magnetization eliminates the impact of linear dia- or paramagnetic materials such as sample matrix, consumable plastics and/or nitrocellulose.Although the intrinsic magnetism of these materials is very weak, with typical susceptibility values of –10−5 (dia) or +10−3 (para), when one is investigating very small quantities of superparamagnetic materials, such as nanograms per test, the background signal generated by ancillary materials cannot be ignored.In MIA based on non-linear magnetic properties of magnetic labels the beads are exposed to an alternating magnetic field at two frequencies, f1 and f2.