What mixtures can be separated by centrifugation?
Heterogeneous mixtures of solid dispersed in liquid, where the dispersed solid and the liquid have a relatively large difference in densities.
The best results are obtained on dispersions where the difference between the density of the dispersed and continuous phases is relatively large. Application of rapid rotation causes the more dense dispersed phase to move away from the axis of rotation, and the less dense continuous phase to move towards the axis of rotation.
This causes the dispersed phase to move and gather in the bottom of the centrifuge tube.
The size and density of a particle and the speed with which it sediments in a heterogeneous mixture under gravity can be shown to vary, such that greater sized and more dense particles sediment at a greater rate. But by increasing the effective gravitational force on the particle via centrifuge sedimentation rate is speeded up significantly.
Particularly stable colloidal dispersions, and those where the dispersed and continuous phases do not have an especially large difference in density may not separate effectively, or may require very specialised ultracentrifugation units (extremely high speeds).