nonmagnetic material such as aluminum to contain the magnetic field at opposite ends of the magnet 20 the operation of the device 10 will now be described in connection with fig1 2 and 8 a biological cell sample fluid is prepared and placed into the cell sample container 32 this sample may be a blood sample prepared in the manner described by the above incorporated patent application the size of the sample may for example be 5 ml pinch valves 44 and 52 are each in an open condition allowing fluid flow through conduits 42 and 50 50 a pinch valve 54 is closed to prevent fluid flow past the pinch valve 54 in conduit 50 b the positive displacement pump 120 is operated at a flow rate of for example 5 ml min to apply vacuum to the system including to the interior of the separated cell container 60 via the pump conduit 64 conduits 50 a 50 leading to the interior annular flow channel of the separator tube 22 as well as conduit 42 sample cell container 32 conduit 36 and the buffer fluid container 34 this applied vacuum draws buffer fluid into the cell sample container 32 approximately 30 ml of fluid is thereby collected in the separated cell container 60 by drawing the 5 ml sample and 25 ml of buffer fluid through the separator tube 22 and into the container 60 during this initial.