Estimation of experimental conditions that permit cell separations by velocity sedimentation on isokinetic gradients of Ficoll in tissue culture medium

In previous papers, I have demonstrated that cell sedimentation in gradients of Ficoll (polysucrose) in tissue culture medium is accurately described by the differential sedimentation equation integrated by a computer to predict the location of cells having specified diameters and densities as a function of time during sedimentation. For the investigator who is working with a specific group of cells, it is cumbersome and time-consuming to adapt our computer program to his computer. Fortunately, the densities of most cells in gradients of Ficoll in tissue culture medium fall within a narrow range of possible densities (1.060–1.120 gm/ml); therefore, it is possible to construct one gradient in which the sedimentation of most mammalian cells will closely approach being isokinetic. The isokinetic gradient reported here begins 13.7 cm from the center of revolution; the necessary dimensions can be obtained in a variety of low-speed centrifuges (I.E.C. PR-2, I.E.C. PR-4, MSE 6L, etc.). Using the previously reported computer-generated numerical integration of the sedimentation equation, a table has been generated that lists the velocities of cells having a wide range of densities and diameters in the isokinetic gradient. Having determined the densities of the cells and their location on the isokinetic gradient at any one centrifuge speed, the investigator can use this table to predict their location on the isokinetic gradient at other centrifuge speeds without using a computer.