Approaches are described for separating plasma from whole blood samples and include the use of magnetically attractable particles associated with an agglutinating agent. The magnetically attractable particles bind the cellular components in a whole blood sample. Application of a magnetic field gradient to a container with the blood sample and the magnetically attractable particles draws the particles to the surface of the container near the source of the magnetic field gradient. The plasma can be removed and stored or used for monitoring or detecting analytes in the plasma.