A centrifuge is a laboratory device used for the separation of gas and fluids based on their respective density. Centrifuges are commonly used in laboratories for the separation of biological molecules from a crude extract. In this article, We describe Guide Filtration Centrifuges and Sedimentation Centrifuges.

They are most often deployed to separate different liquids and solid particulates from fluids. Other than mechanical separation, they are also used extensively for gases. In a centrifuge, the sample is placed in a rotor that is rotated about a fixed axis. 

This results in the creation of a strong force perpendicular to the axis, which separates the particulates from the mixture. Though you can find a vast array of centrifuges, they all work on the principle of sedimentation. 

Working Principle of a Centrifuge

The centrifuge derives its name from the centrifugal force. Centrifugal force is a virtual force that pulls spinning objects and particulates outwards. The best way to understand the centrifugal force is by citing an example of a bucket of sand and water. 

If you fill a bucket with a mixture of sand and water, spinning the bucket produces centrifugal force. Here the sedimentation principle can also be applied to understand the concept better. As per the sedimentation principle, both sand and water would be drawn to the bucket’s outer edge. 

However, as sand particles have more density, they would settle in the bottom. On the other hand, the lighter water molecules would be displaced centrally—a centrifuge function in a similar manner which results in the separation of molecules. 

Significance of Rotors in a Centrifuge 

Without rotors, you cannot separate molecules from a sample. Rotors refer to those devices which house the test-tubes with the samples. Being an important component, they are constructed in a manner so that there is high rotation speed. Some of the common rotors used in a centrifuge nowadays are:

• Horizontal Rotors

In these rotors, you would find the test-tubes suspended in racks. In the case of horizontal rotors, the particles are present along the direction of the force. 

• Fixed Angle Rotors

In these rotors, you would find the test-tubes at an angle of 45-degree concerning the rotor’s axis. Centrifuges with these rotors are faster and hence used extensively. 

• Vertical Centrifuge Rotors

Out of all types of centrifuge rotors, vertical rotors provide the shortest path length. However, the results obtained from vertical centrifuge rotors are not accurate. This is because the position of the test-tubes doesn’t align with the force’s direction. 

What are the Filtration Centrifuges?

The working principle of filtration centrifuges is based on the highly accelerated form of sedimentation. Filtration centrifuges are based on the gravity and centrifugal force to separate particles heavier than the liquids. Filtration centrifugation is an accelerated form of sedimentation. 

To be precise, a majority of filtration methods use filter media to eliminate impurities. The solid material is usually collected and removed. In the case of filtration centrifuges, the solid particles can be separated and collected. 

In other words, filtration centrifuges don’t dispose of solid particles like traditional filters. This is especially used when there is a need to collect solid particulates for further research. 

Reasons to opt for Filtration Centrifuges 

For many researchers out there, filtration centrifuges are one of the effective devices to separate solids from mixtures. So here are some specific reasons to opt for filtration centrifuges. 

• Elongates tooling life
• Decreases volume of disposal and related costs
• Ability to discharge solids automatically
• Improves the overall product quality 
• Ability to operate without human intervention
• Consumes less power when compared to other centrifuges 

Working Principle of Modern-Day Filtration Centrifuges 

The mixture containing the liquid and solid particles is placed in the test-tubes of the centrifuge. As the centrifugal forces extract solids and packs than to the test-tube walls, it is fairly easy to separate them. What’s more, many present-day filtration centrifuges are automated, which implies that there is no manual intervention required. Filtration Centrifuges are standard equipment for a wide variety of industries. However, they are most commonly used by the chemical process industries.  

The Basics of Sedimentation Centrifuges

The mechanics of sedimentation centrifuging makes it suitable for two-phase systems that have a high-density differential. Most commonly, sedimentation centrifuges are used for analytical ultracentrifugation. With these centrifuges, you can find the molecular mass of a macromolecule. 

The sedimentation velocity approach or sedimentation equilibrium methodology is the other working principle of centrifuges. With the help of sedimentation, you can obtain the sedimentation coefficient. The sedimentation coefficient can be used to record transformations in the overall shape and size of the macromolecules. 

Even under changing experimental conditions, you can use sedimentation centrifuges to get the right results. 

Sedimentation Centrifuges and Density Gradient Centrifugation

Sedimentation Centrifuges can also be used to achieve density gradient centrifugation under normal laboratory conditions. In this type of centrifugation, the separation is based on the overall density of the particulates present in the mixture. 

Molecules in the sample pass through the medium as the sedimentation principle is applied, which either increases or decreases the density. At a certain point in time, the molecules become suspended, and the density of the particles equals the surrounding medium.         

Factors influencing the Sedimentation Centrifuges

Here are some of the factors which influence the functioning of sedimentation centrifuges. 

• Viscosity of the Mixture
• Rotation Speed
• The density of the solution
• Distance to which particulates are scattered inside the centrifuge 

 Note that at a regular centrifugal force and viscosity, the sedimentation rate is proportional to the size of the molecules. A sedimentation centrifuge is also based on the principle that the greater the difference in density, the faster the molecules would move.    

Apart from the centrifuges as mentioned above, you can find their other types. From microcentrifuges to general-purpose centrifuges, modern-day labs have a lot of options. Medium-size centrifuges are common in our daily life too. For instance, washing machines use the principle of centrifugation during spinning. Understanding the daily applications of centrifuges would urge others to know about them. 

Author’s Bio

Patricia Hopkins has been the Managing Director of a major centrifuge manufacturing company. She possesses extensive experience in various aspects of industrial and lab-based centrifuges.