A centrifuge apparatus is used for collecting white blood cells (WBC), primarily mononuclear cells, from whole blood stratified into layers. A thin mononuclear (MNC) layer is formed at the interface of red blood cells and plasma. A barrier is positioned in the separation vessel of the centrifuge...http://www.google.ca/patents/US5704889?utm_source=gb-gplus-sharePatent US5704889 - Spillover collection of sparse components such as mononuclear cells in a centrifuge apparatus 
