Centrifugation Definition and Meaning

Centrifugation is called the act of centrifuging: using centrifugal force to achieve the separation of the components of a mixture or the drying of certain materials.

A centrifugal force is that manifested in bodies that develop a curved path. This force is equal to but contrary to the centripetal force, which is directed radially towards the center.

Centrifugation, in short, consists of the use of centrifugal force to separate elements according to density or to dry something. The machine that supplies the centrifugal force is called a centrifuge.

What a centrifuge does is accelerate the sedimentation or decantation process of the phases of a mixture. This is possible thanks to the different densities of the components. By centrifugation, in this way, the serum can be separated from the plasma in the blood or the pulp of a fruit juice, to name two possibilities.

The solids that can be separated by the use of centrifugation are insoluble, that is, they do not form a solution with a liquid. When a liquid is mixed with an insoluble solid, a heterogeneous system is produced in which it is possible to see solid particles suspended within the other substance. Centrifugation is only one of the unit separation operations of this class of solids; the other four are: filtration, elutriation, sedimentation, and flotation.

When a considerable centrifugal field is applied to such a pair (liquid and insoluble solids), the particles tend to move through the fluid by the action of acceleration (angular velocity squared by radius).

The centrifugal force writes a motion in a rotating reference frame or, equivalently, the apparent force that a non-inertial observer perceives (that is, that does not comply with Newton’s laws of motion; in this particular case, the observer should present an accelerated motion relative to the rotating reference frame).

Types of centrifugation:

* Differential: it is based on the difference in density of the molecules, which must be considerable so that it can be observed during centrifugation. Particles with similar densities settle together. It should be noted that this method is considered “nonspecific”, and therefore it is used as a preparation to separate the components of the mixture but not for the separation of molecules. For example, it serves for the separation of membrane mitochondria and nuclei;

* Isopycnic: it is based on the fact that if media of different density are used it is possible to separate particles with the same sedimentation coefficient. Its use is very common to separate DNA;

* Zonal: with this type of centrifugation it is achieved that the difference in the sedimentation speed leads to the separation of the particles, as they all have different masses. The sample must be placed on a density gradient by means of which the centrifugal force makes sedimentation occur at different speeds, depending on the mass. If the centrifugation time is too long, the particles may settle at the bottom of the tube.

It is common for washing machines (also known as washers) to have a spin option. These machines that are used to wash clothes have an electric motor and a drum where dirty clothes are introduced. This drum is filled with soap and water and moves quickly thanks to the motor, washing clothes. To dry the garments, the machine performs a centrifugation process.

The spin stage reduces the moisture in the clothes, as the centrifugal force causes the water to separate from the fabrics. In this way the centrifugation dries the clothes.


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