In bioseparation, magnetic particles can be used for the adsorption of biomolecules. They can be selectively separated from multi-component suspensions with high-gradient magnetic separation (HGMS). A single-use HGMS separation chamber has been developed to avoid cross-contamination. As with fixed-bed adsorption, breakthrough occurs after a certain time. Subsequently, the magnetic particles that are then still further fed, are lost together with the biomolecules bound to them. In order to stop the HGMS process before breakthrough, an associated optical measurement method was developed.