The working principle of a centrifuge

Release time:

2014-02-18

Overview:

Centrifugation utilizes the powerful centrifugal force generated by the high-speed rotation of a centrifuge rotor to accelerate the sedimentation rate of particles in a liquid, thereby separating substances in a sample that differ in their sedimentation coefficients and buoyant densities.

When a suspension containing fine particles is left undisturbed, the particles suspended in the liquid gradually settle down under the influence of the gravitational field. The heavier the particles, the faster they sink; conversely, particles with a density lower than that of the liquid will rise to the surface. The rate at which particles move under gravity depends on their size, shape, and density, as well as on the strength of the gravitational field and the viscosity of the liquid. Particles on the order of red blood cell size—typically several micrometers in diameter—can be observed undergoing sedimentation even under normal gravitational conditions.

　　Moreover, as substances settle in a medium, they are accompanied by the phenomenon of diffusion. Diffusion is unconditional and absolute. It is inversely proportional to the mass of the substance—thus, the smaller the particles, the more severe the diffusion. In contrast, sedimentation is relative and conditional; it requires external forces to occur. Sedimentation is directly proportional to the weight of the object—hence, the larger the particles, the faster they settle. For particles smaller than a few micrometers—such as viruses or proteins—when they exist in solution in a colloidal or semi-colloidal state, it is simply impossible to observe the sedimentation process by relying solely on gravity. This is because the smaller the particles, the slower their sedimentation becomes, while the diffusion phenomenon becomes increasingly pronounced. Therefore, it is necessary to use a centrifuge to generate a powerful centrifugal force, which can overcome diffusion and induce sedimentation in these tiny particles.

Classify centrifuges according to the separation factor.

The difference between industrial centrifuges and laboratory centrifuges