We explain what centrifugation is as a method of separating mixtures. Also, types of centrifugation and some examples.

Centrifugation is a method of separating mixtures that uses centrifugal force.

What is centrifugation?

Centrifugation is a mixture separation mechanism(in particular, those composed of solid Y liquids differently density) through its exposure to a rotating force of a certain intensity.

This force, known as the centrifugal force in the Newtonian mechanics, is a fictitious force that appears when a body describes a movement rotation. Its name means "that flees from the center", since it moves away from the axis of rotation of the body's trajectory.

Centrifugal force causes objects to move away from the center as they rotate. For example: when a fisherman spins the hook before casting it into the sea, or the force that pushes us against the seat in the rotating attractions of the amusement parks. It is the same that uses a centrifuge, or apparatus capable of generating centrifugal force, to separate mixtures in a lab.

Centrifugation works by pushing the densest components of the mixture towards the point furthest from the axis of rotation and leaving the least dense at the closest point. Is technique it is in everyday use by chemists, biologists, and other scientists.

Examples of centrifugation

Centrifugation allows the different components of the blood to be separated.

Centrifugation is used in numerous cases of scientific study, especially of the basic substances of theorganic material. Through specialized processes of centrifugation of substances such as blood orcells In humans, plasma, platelet concentrates, intracellular organelles, and even DNA.

Other simple examples are the washing machine, which uses centrifugal force to, after mixing the Water, soap and clothes, dry them, eliminating the water through the holes in the drum, thanks to the centrifugal force; or the machines of theindustry dairy products that extract from the milk the portions of fat that we must remove to obtain skim milk and to make whey, cream and others products.

Types of centrifugation

There are four types of centrifugation:

  • Differential centrifugation. Take advantage of the difference in sedimentation speed of the differentmolecules of a mixture. Thus, particles of similar densities settle together. It is usually used to separate components of a mixture and constitutes the preparatory step for molecule separation processes.
  • Isopycnic centrifugation. Adds media of different density to particles that share the same sedimentation coefficient, so that they can be separated by centrifugal force.
  • Zonal centrifugation. It separates the particles of a mixture based on their difference in sedimentation rate and also their mass, since the mixture is previously placed on top of a preformed density gradient, acting as a particle “strainer” thanks to centrifugal force.
  • Ultracentrifugation. Monitor the structures using ultraviolet light or interferometers, as they settle, using rotor systems (fixed or swing). It is very useful for studying subcellular structures.

Other methods of separating mixtures

Filtering is a method that allows solids to be separated from a mixture.

Apart from centrifugation, mixtures can be separated by physical or chemical processes such as:

  • Filtered out. A mesh or retention material is used that allows the passage of the liquid solvent (water, for example), but retains the larger solids present in it (coffee grounds, for example).
  • Sieving. It is a technique similar to filtering, but it allows the separation of solids of different sizes, using a sieve whose holes allow the passage of certain solids and retain the larger ones.
  • Evaporation selective. To separate mixtures of liquids, or of solids and liquids, the difference in Boiling point (or melting point, in the case of solids), heating the mixture until the liquid (or one of them) evaporates and leaving the solids (or the liquid with a lower boiling point) in the container.
  • Decantation. Using a suitable container, a mixture of liquids, or of solid and liquid, is separated, first allowing the gravity attract the densest components to the bottom of the container. The least dense will be at the top. Then the densest component will be extracted by opening a hole in the bottom.
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