The Centrifuge – Definition, Principle, Types and Applications

centrifuge

The centrifuge is an electrical device that separates various components in a fluid-rising centrifugal force. It is generally driven by an electric motor that puts an object to rotate around a fixed axis, and a perpendicular force is applied to the axis. The sedimentation of the particles basically depends on various factors, including size shape, and density. Similarly, the viscosity of the medium and rotor speed are some other influencing factors. This is achieved by spinning the fluid at high speed within a container which thus separates the fluids of different densities.

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Definition of The Centrifuge

The centrifuge is a device that does centrifugation by the use of centrifugal force generated in a spinning rotor to separate biological particles. These particles include cells, viruses, sub-cellular organelles, macromolecules (mainly proteins and nucleic acids and macromolecular complexes. As the rotor spins the denser particles move outward in the radial direction. On the other hand, objects that are less dense are displaced and moved to the centre. Therefore this technique of separation by radial acceleration is widely used for the separation of contaminants from body fluids.

History behind the invention of the centrifuge

  • The idea of a centrifuge was first proposed by Antonin Prandtl in 1864. It was an idea of a dairy centrifuge based on the separation of cream from milk.
  • Later on, his brother Alexander Prandtl made improvements in his designs and worked on butterfat extraction in around 1875.
  • In the early 1900s, major centrifugal advances led to medical breakthroughs. Following Prandtl, a Swiss physician and biologist, Friedrich Miescher, was the first to apply centrifugation in the lab.
  • The first centrifuge that successfully separated individual atoms of different weights was made by Jesse Beams in 1934.

Working Principle Of The Centrifuge

Centrifugation is used to separate all types of particle-based on their sedimentation properties. It is based on the principle of sedimentation. Thus in its case, the acceleration at centripetal force causes denser substances to separate out along the radial direction at the bottom of the tube of the centrifuge. By the same concept, lighter objects will tend to move to the top of the tube. As seen in the rotating picture, move to the centre. The greater the difference in densities the faster the components will separate out.

However, both density and shape vary significantly depending on the composition of the components of the solution in which the particles are suspended.

Even tiny differences in density separate various particles in a solution. Gravity can thus be replaced with the much more powerful “centrifugal force” provided by a centrifuge. Therefore, it’s the centrifugal force that comes into play while centrifugation. This centrifugal force is directly proportional to the rotation rate of the rotor.

The centrifugal force generated by a centrifuge can easily be calculated from the equation:
                                               RCF= 11.8 * r * (RPM/1000)²
here,
RCF= the relative centrifugal force
r = the distance from the centre of rotation in centimetres
RPM= Rotations per minute  (speed of centrifugation)
As stated generally, the higher the centrifugal force shorter the separation time. However, the hydrostatic force generated in the solution while centrifugation can disrupt the biological particles such as ribosomes.

Types Of Centrifuge

Density Gradient Centrifuge

  • The density gradient method of centrifugation is used to separate macromolecules with a slight difference in their size or densities. It allows the separation of many or all components in a mixture. It allows for their measurement also.
  • The rate of movement of components in the solution basically depends on their molecular mass. Drilling a hole into the centrifugation tube and allowing the contents to drip out will make it possible to collect the different particles in separate fractions.
Density gradient centrifuge

Image source: Li, P., Kumar, A., Ma, J., Kuang, Y., Luo, L., & Sun, X. (2018). Density gradient ultracentrifugation for colloidal nanostructures separation and investigation. Science Bulletin, 63(10), 645-662.

  • It includes two forms are mentioned below:

RATE ZONAL CENTRIFUGATION

♦ As mentioned this type of centrifugation has a density gradient. Therefore this gradient of components is used to linearize the motion of the particles. In rate zonal centrifugation, the sample is applied with centrifugal force in a thin zone at the top of the centrifuge tube on a density gradient. The particles will begin sedimenting through the gradient under the influence of centrifugal force. This happens in separate zones according to their size shape and density. This spinning process is terminated before any of the separated particles reach the bottom of the tube.

ISOPYCNIC OR SEDIMENTATION EQUILIBRIUM CENTRIFUGATION

♦In this type of centrifugation, the solution in the centrifuge contains a greater range of densities. Therefore the density gradient column encompasses the whole range of densities of the sample particles. Then the sample is uniformly mixed with the gradient material in the sample pool. Each particle will sediment only to the position in the centrifuge tube at which the gradient density is equal to its own density. Then it will remain there.

♦This method is very useful for isolating membranes and organelles that have very diverse sizes but have the same functions. They have the same composition and so they have very similar densities. The choice of rotors for isopycnic centrifugation depends on the nature of the sample. For example, for larger particles such as organelles, it is best to use a swinging bucket rotor. on the other hand, in the case of macromolecules better results in terms of gradient capacity and resolution should be obtained using a fixed-angle rotor.
 Rate-zonal centrifugation B – Isopycnic centrifugation

Image source: Ermolin, M. S., & Fedotov, P. S. (2016). Separation and characterization of environmental nano-and submicron particles. Reviews in Analytical Chemistry, 35(4), 185-199.

Moving Boundry/Zone Centrifuge

  • Moving boundary or differential centrifugation the entire tube is filled with sample. Then it is centrifuged inside it. It is the most frequently used separation technique.
  • While centrifugation, the separation of two particles is obtained. The particles may end up in the supernatant or the pellet or may be distributed in both fractions depending on their size, shape, density and conditions of centrifugation. The two fractions are recovered by decanting the supernatant solution from the pellet.
  • It is commonly used in microbiology and cytology to separate organelles for further analysis. In this process, the tissue sample is homogenized and the cell contents are mixed up after breaking the cell walls.
  • Thus the homogenate obtained is then subjected to repeated centrifugation, each time removing the pellet and increasing the centrifugal force.
centrifuge

Image source: nios.ac.in

Ultracentrifugation

  • The first-ever ultracentrifuge was an analytical centrifuge that was developed by Svedberg. It was first used commercially in 1940.

    commons.wikimedia.org

  • Like all subsequent analytical centrifuges, it has the unique feature that the sample was centrifuged in a cell with transparent sides and so it is possible to view and analyze the sedimentation process during centrifugation.
  • It is especially useful for studying the molecular interactions of macromolecules. Predominantly polysaccharides and other types of macromolecules that cannot be analysed by the usual analytical methods such as gel electrophoresis, ultracentrifugation works efficiently.

Applications Of The Centrifuge

  1. Production and separation of biological products
  2.  Determination of the molecular mass of the components of the centrifuge such as the collides.
  3. Useful in water treatment.
  4. Separation of particles from an airflow using cyclonic separation.
  5.  Isotopic separations
  6. Used for the separation of cream from milk
  7.  Used in the oil industry to remove solids from the drilling fluid.
  8. Wide applications in aeronautics and astronautics

 

At last, it would be correct to state that the choice of centrifugation method depends on the nature of the particles, and often more than one separation technique is required. Also, rotor safety is very important and rotors made of aluminium alloys are very susceptible to severe corrosion even when left to soak in water overnight. Titanium or carbon composite rotors are supposedly used as rotors made of aluminium alloys and are very susceptible to severe corrosion even when left to soak in water overnight. Following the measures mentioned by the manufacturers, the centrifuge is a very helpful device. Therefore it is extensively used in the field of biotechnology.

Thanks for reading!

Team MBD

Watch here- Density gradient centrifugation – YouTube

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4 Responses

  1. Anamika Singh says:

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  3. Hera says:

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  4. Aditi Singh says:

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