Types of Centrifugation with Principles and Uses

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Centrifugation is a mechanical process that utilizes an applied centrifugal force field to separate the components of a mixture according to their density and/or particle size . The process relies on the centrifugal force created when a sample is rotated about a fixed point. The denser molecules move towards the periphery while the less dense particles move to the center. Centrifugation is commonly used in molecular biology to collect cells, precipitate DNA, purify virus particles, and distinguish subtle differences in the conformation of molecules .

Centrifugation can be performed in different ways depending on the purpose and the nature of the sample. Some of the factors that affect the centrifugation process are:

  • The speed of rotation (measured in revolutions per minute or RPM)
  • The time of centrifugation
  • The temperature of the sample
  • The volume and shape of the sample tube
  • The density and viscosity of the medium
  • The size and shape of the particles
  • The presence or absence of a density gradient

The speed of rotation determines the magnitude of the centrifugal force applied to the sample. The higher the speed, the greater the force and the faster the separation. However, too high a speed can also damage or deform the particles or cause them to aggregate. Therefore, the optimal speed for each sample must be determined empirically.

The time of centrifugation affects how far the particles travel in the medium. The longer the time, the more complete the separation. However, too long a time can also cause diffusion or mixing of the particles or cause them to lose their biological activity. Therefore, the optimal time for each sample must be determined empirically.

The temperature of the sample affects the viscosity and density of the medium as well as the stability and activity of the particles. The higher the temperature, the lower the viscosity and density and the faster the separation. However, too high a temperature can also denature or degrade the particles or cause them to lose their biological activity. Therefore, the optimal temperature for each sample must be determined empirically.

The volume and shape of the sample tube affect how evenly and efficiently the sample is distributed in the medium and how easily it can be recovered after centrifugation. The smaller and more symmetrical the tube, the better. However, too small a tube can also limit the amount of sample that can be processed or cause excessive heating or friction. Therefore, an appropriate tube size for each sample must be selected.

The density and viscosity of the medium affect how easily and quickly the particles move through it under centrifugal force. The higher the density and viscosity, the slower and more difficult the separation. However, too low a density and viscosity can also cause insufficient separation or loss of particles. Therefore, an appropriate medium for each sample must be selected.

The size and shape of the particles affect how they respond to centrifugal force and how they interact with each other and with the medium. The larger and more spherical the particles, the faster and more efficiently they separate. However, too large or irregular particles can also cause incomplete separation or aggregation. Therefore, an appropriate particle size and shape for each sample must be selected.

The presence or absence of a density gradient affects how finely and accurately the particles can be separated based on their density differences. A density gradient is a medium that has a gradual change in density from top to bottom. When a sample is layered on top of a density gradient and centrifuged, each particle will migrate to a position where its density matches that of the surrounding medium. This allows for better resolution and identification of particles with similar densities than using a uniform medium. However, creating and maintaining a density gradient can also be more complex and costly than using a uniform medium. Therefore, an appropriate density gradient for each sample must be selected.

Centrifugation is a versatile and powerful technique that can be used for various purposes in different fields. In this article, we will discuss some of the different types of centrifugation, their principles, steps, and uses.