Principle of centrifugation

When the suspension containing fine particles is standing still, the suspended particles gradually sink due to the action of the gravity field. The heavier the particles, the faster they sink, otherwise the particles with a lower density than the liquid will float up. The speed of particles moving under the gravity field is related to the size, shape and density of the particles, and is related to the strength of the gravity field and the viscosity of the liquid. Particles the size of red blood cells, with a diameter of a few microns, can observe their sedimentation under normal gravity.

When the suspension containing fine particles is standing still, the suspended particles gradually sink due to the action of the gravity field. The heavier the particles, the faster they sink, otherwise the particles with a lower density than the liquid will float up. The speed of particles moving under the gravity field is related to the size, shape and density of the particles, and is related to the strength of the gravity field and the viscosity of the liquid. Particles the size of red blood cells, with a diameter of a few microns, can observe their sedimentation under normal gravity.

In addition, when the substance settles in the medium, it is accompanied by a diffusion phenomenon. Diffusion is absolute and unconditional. Diffusion is inversely proportional to the mass of the substance, the smaller the particle, the more serious the diffusion. The settlement is relative, conditional, and can only be exercised by external forces. The sedimentation is proportional to the weight of the object, the larger the particles, the faster the sedimentation. For particles smaller than a few microns, such as viruses or proteins, which are in a colloidal or semi-colloidal state in solution, it is impossible to observe the sedimentation process using gravity alone. Because the smaller the particles, the slower the settling, and the more serious the diffusion phenomenon. Therefore, it is necessary to use a centrifuge to generate a strong centrifugal force in order to force these particles to overcome the diffusion and generate a settling motion.

Centrifugation is to use the powerful centrifugal force generated by the high-speed rotation of the centrifuge rotor to accelerate the sedimentation speed of particles in the liquid, and separate the substances with different sedimentation coefficients and buoyancy density in the sample.