How does a bottle centrifuge separate substances in laboratory test tubes?

A bottle centrifuge separates substances by utilizing centrifugal force to substitute for and intensify the effects of gravity.12

In this batch-type process, test tubes or bottle-type containers are mounted symmetrically on a rotor driven by an electric motor or other power source. The containers are typically supported by high-strength metal holders so that their axis is perpendicular to the axis of rotation. As the rotor spins, the centrifugal field forces suspended particles denser than the surrounding liquid to migrate radially toward the periphery (the bottom of the tube), while less dense components move toward the center.12

To improve efficiency, some models hold the tubes at an angle of approximately 37° to the axis of rotation, which reduces the distance the material must settle. By varying the speed of rotation, the centrifuge can generate forces ranging from a few times gravity up to tens of thousands of g, allowing for the effective separation of solids from liquids or the clarification of mixtures that would otherwise take an impractical amount of time to settle naturally.1