Blood separation. Technician putting a sample of blood into a centrifuge (below surface) in an isolator unit. A centrifuge is a machine that spins its contents around a central axis at very high speeds. The force created by the spinning separates groups of particles according to their densities. Centrifuged blood is separated into red blood cells, white blood cells and plasma. The constituents can then be analysed for signs of illness, infection or for blood type. The isolator unit, whose interior is sterile, is used to prevent contamination of the sample.