We explain what centrifugation is as a method of separating mixtures. Also, types of centrifugation and some examples.
What is centrifugation?
Centrifugation It is a mechanism for separating mixtures (in particular, those composed of solids and liquids of different densities) through their exposure to a rotating force of a certain intensity.
This force, known as centrifugal force in Newtonian mechanics, is a fictitious force that appears when a body describes a rotational movement. 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 throwing it into the sea, or the force that pushes us against the seat on the spinning attractions at amusement parks. It is the same as that used by a centrifuge, or device capable of generating centrifugal force, to separate mixtures in a laboratory.
Centrifugation operates by pushing the densest components of the mixture toward the point furthest from the axis of rotation and leaving the least dense ones at the closest point. This technique is used daily by chemists, biologists and other scientists.
See also: Homogeneous mixture
Examples of centrifugation
Centrifugation is used in numerous cases of scientific study, especially of the basic substances of organic matter. Through specialized centrifugation processes of substances such as blood or human cells, plasma, platelet concentrates, intracellular organelles can be separated and even DNA.
Other simple examples are the washing machine, which uses centrifugal force to, after mixing the water, soap and clothes dry it, eliminating water through the holes in the drum, thanks to centrifugal force; or the dairy industry machines that extract from milk the portions of fat that we must remove to obtain skim milk and to manufacture whey, cream and other products.
Types of centrifugation
There are four types of centrifugation:
- Differential centrifugation It takes advantage of the difference in sedimentation speed of the different molecules in 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 Add media of different density to particles that share the same sedimentation coefficient, in order to separate them using centrifugal force.
- Zonal centrifugation It separates the particles of a mixture based on their difference in sedimentation speed and also their mass, given that the mixture is previously placed on top of a preformed density gradient, acting as a “strainer” for particles thanks to the centrifugal force.
- Ultracentrifugation Monitor structures using ultraviolet light or interferometers, as they settle, using rotor systems (fixed or swing). It is very useful for studying subcellular structures.
Other mixture separation methods
Apart from centrifugation, mixtures can be separated by physical or chemical processes such as:
- Filtered A mesh or retaining 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).
- Sifted It is a technique similar to filtering, but that allows solids of different sizes to be separated, using a sieve whose holes allow the passage of certain solids and retain the larger ones.
- Selective evaporation To separate mixtures of liquids, or of solids and liquids, the difference in boiling point (or melting point, in the case of solids) can be taken advantage of, heating the mixture until the liquid (or one of them) evaporates and leaving it in solids (or lower boiling liquid) in the container.
- Decantation Using a suitable container, a mixture of liquids, or solid and liquid, is separated, first allowing gravity to draw the denser components to the bottom of the container. The least dense will be on top. Then the densest component will be extracted by opening a hole in the bottom.
Continue with: Chemical suspension
References
- “Centrifugation” on Wikipedia.
- “Centrifugation” (video) at the Polytechnic University of Catalonia (UPC).
- “Centrifugation” in Biomodel.
- “What is centrifugation?” at TP Chemical Laboratory.
- “What is Centrifugation?” on Study.com.
