The supernatant incorporates non-certain cells and particles that may be discarded, leaving only your pure target cells connected to the bead. Fig. one: Workflow of a typical protein purification procedure working with magnetic beads/MagBeads. In depth technical specs of the person steps regarding how to use magnetic beads are supplied https://www.quora.com/profile/Even-Sa/What-is-the-application-range-of-magnetic-beads-The-application-scope-covers-nucleic-acid-extraction-and-purification