Centrifuge: Principle, Types and Application

What is a centrifuge?

A centrifuge is a powerful device utilized for separating and purifying mixtures by employing centrifugal force. It effectively separates particles based on their size, shape, density, viscosity, and rotor speed. The process involves the sinking of particles with higher density to the bottom while the lighter ones float to the top. This innovative instrument enables efficient separation and purification of substances by utilizing the force generated through rapid spinning. By leveraging centrifugal force, a centrifuge facilitates precise particle separation and purification, making it an indispensable tool in various fields.

Principle of centrifuge

The principle behind centrifuges is the sedimentation principle, which is employed by all types of centrifuges. In this principle, the acceleration of the rotor initiates a centripetal force that acts upon both the rotor and the centrifuge tubes. To achieve this, a device is designed to rotate the solution around a fixed axis, with the force applied perpendicular to the axis of the spin. As a result of this action, denser particles move outward in a circular direction, while lighter particles move toward the center.

The rate of sedimentation is influenced by several factors, including the applied centrifugal field (G). Additionally, other factors such as the mass, density, and volume of the particles, as well as their shape and friction, contribute to the sedimentation process.

Types of centrifuges:

Depending on the sedimentation speed, vacuum, temperature control refrigeration, volume of sample, capacity of refrigeration tubes, size and design, there are nine commonly used:

1. Micro centrifuge
2. Small bench top centrifuge
3. Refrigerated centrifuge
4. High speed refrigerated centrifuge
5. Low speed centrifuge
6. Ultracentrifuge
7. Continuous flow centrifuge
8. Gas centrifuge
9. Vacuum centrifuge

Micro centrifuge:

• Micro centrifuge is extremely small in design and takes up little space in the working area which is an advantage.
• Small tube size up to 2.0 ml is used in this type with 500 rpm to 13300 rpm speed range.
• It is applicable in holding pelleting nucleic acids, pelleting proteins from solution and micro filtration of minor aqueous samples.

 Small bench top centrifuge:

• Small bench top centrifuge is commonly used in clinical laboratory for separating blood for plasma or serum, urine and body fluid separation.
• The instrument is small with maximum speed of 3000 rpm and can take approximately 100 tubes depending on diameter.

Refrigerated centrifuge:

• Refrigerated centrifuge are used for those samples that need to be stored at consistent temperature to make the sample perfect for analyzing.
• The temperature ranges from -20 to -40 degree Celsius and can go up to maximum of 6500 g centrifugal force.
• It is used for analyzing DNA, RNA, PCR, antibodies, yeast cells, chloroplast etc.

High speed refrigerated centrifuge:

• The maximum speed of this high speed refrigerated centrifuge is 25000 rpm which is known for its name with 90000 g centrifugal force.
• The temperature in high speed refrigerated centrifuge is maintained at 0 to 4°C and the refrigeration is equipped to remove the generated heat during processing.
• This is used to collect cell debris, large cellular organelles and sub cellular organelles, precipitates of chemical.

Low speed centrifuge:

• The maximum speed is 4000 to 5000 rpm and should be operated under room temperature as speed and temperature controlling system is not included in the device.
• Low speed centrifuge is ideal for the analysis of blood samples and other biological samples.

Ultracentrifuge:

• Ultracentrifuge operates at the speed of 75000 rpm with 500000 g centrifugal force at 0 to 4°C refrigeration system.
• It has an ability to differentiate between molecules like proteins and nucleic acids for separation.
• There are two types of ultracentrifuges: Preparative and Analytical ultracentrifuge.
• Preparative ultracentrifuge separates macromolecules, lipoprotein fractions from plasma and deprotonizes physiological fluids for amino acid analysis. It produces up to 600000 g of centrifugal force.
• Analytical ultracentrifuge contains a light based optical detection system for analysis of light absorption system, the alternative Schlieren system and the Rayleigh interferometric system. It produces 500000 g of centrifugal force.

Continuous flow centrifuges:

• A large volume of sample can be continuously processed in continuous flow centrifuge, the samples do not need to be loaded and unloaded over and over again which saves time.
• High volume of sample up to 1 liter can be centrifuged at 4 hours or less in time.

Gas centrifuge:

• Gas centrifuge is mainly used for the separation of Uranium-235 and Uranium-238.
• This works on the continuous flow of gas in and out and separates gases on the basis of their isotopes and masses.

Vacuum centrifuge:

• Vacuum centrifuge is also known as concentrators and are used for the evaporation of solvents present in the sample.
• They are used in chemical and biological laboratories where sample with large number of solvent is present.

Applications of Centrifuge

1. Separation of Mixtures: Centrifuges are widely used for the separation of mixtures containing molecules with similar densities or immiscible liquids. By subjecting the mixture to centrifugal force, the components can be effectively separated based on their varying densities and physical properties.
2. Blood Component Separation: One of the essential applications of centrifuges is in the medical field for separating blood components. Centrifugation enables the separation of blood cells from plasma or serum, which is crucial for various diagnostic and analytical procedures.
3. Analysis of Blood Samples: Centrifugation plays a vital role in laboratory analysis. By separating blood components, it facilitate the analysis of various parameters such as cell counts, hematocrit levels, and identification of disease markers.
4. Immunochemical Assays: They are utilized in immunochemical assays to separate protein-bound ligands from free ligands. This separation enables accurate measurement and detection of specific molecules, aiding in research, diagnostics, and drug development.
5. Isotope Separation: Centrifuges have significant applications in isotope separation, particularly in nuclear industries and scientific research. By utilizing the varying masses of isotopes, centrifugation can effectively separate isotopes for further analysis or industrial purposes.
6. Subcellular Organelle Isolation: Centrifugation is crucial in cell biology and molecular biology for isolating subcellular organelles. By subjecting cell suspensions to centrifugal force, different organelles such as mitochondria, nuclei, and lysosomes can be separated, enabling detailed study and analysis of their functions.
7. Nucleic Acid Extraction: Centrifuges are instrumental in extracting nucleic acids, including RNA and DNA, from biological samples. By separating cellular components, centrifugation aids in the isolation of nucleic acids for applications in genetic research, forensics, and diagnostic testing.