A note on the use of centrifuge in biology.

1. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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Use of Centrifuge
Centrifugation is a technique that involves the application of centrifugal force to
separate particles from a solution according to their size, shape, density, viscosity of
the medium, and rotor speed. A centrifuge is a device for separating particles from a
solution via centrifugation.
USES OF CENTRIFUGES
Centrifuges are used for the following purposes:
Laboratory Separations: A wide variety of laboratory-scale centrifuges are used for
isolating and separating suspensions and immiscible liquids. One such application in
laboratories is blood separation. Blood separates into cells (erythrocytes, leucocytes,
platelets, etc.), proteins, and serum. DNA preparation is another common application
for pharmaco-genetics and clinical diagnosis.
Cell Fractionation: Cell fractionation can be defined as the process of separation of
similar and homogeneous sets of organelles from a heterogeneous population of cells.
This process can also be used to isolate a part of the cell, i.e. mitochondria, DNA,
RNA, ribosomes, etc. There are three steps involved in the process of cell
fractionation:
 Cell Disruption: It is the liberation of biological and organic molecules present within
a cell. The power needed for the disruption of some cells is quite high. The tissue
is homogenized in a solution in which the water content is maintained equal to the
water content within the cell. Other methods like mincing, chopping, osmotic shock
are used to liberate the cell organelles from the cell. Sometimes, the tissue is kept
in ice-cold water or a buffered solution to prevent damages and to prevent any
change in the chemical composition in the cell.
 Filtration: This step involves the filtering out of the macro-sized particles that can
come along with the cell organelle. This step is not mandatory in some cases. But

2. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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during the fractionation of animal tissues, filtration through gauze or a suction filter
is necessary to leave out the fluid connective tissues as a residue.
 Purification & Segregation: The filtrate obtained in the previous step is rotated at a
very high speed thereby increasing the gravitational force sequentially. The
different organelles are segregated according to their density within the test tube.
This process is called centrifugation.
Figure: The process of cell fractionation.
Isotope Separation: Some centrifuges separate isotopes, and these kinds of
centrifuges are in use in nuclear power and nuclear weapon programs. Gas
centrifuges are used in uranium enrichment. The heavier isotope of uranium (uranium-
238) in the uranium hexafluoride gas tends to concentrate at the walls of the centrifuge
as it spins, while the desired uranium-235 isotope is extracted and concentrated with
a scoop selectively placed inside the centrifuge. It takes many thousands of
centrifugations to enrich uranium enough for use in a nuclear reactor (around 3.5%
enrichment), and many thousands more to enrich it to weapons-grade (above 90%
enrichment) for use in nuclear weapons.
Synthesis Of Materials: High gravity conditions generated by centrifuge is applied in
the chemical industry, casting, and material synthesis. The convection and mass
transfer are greatly affected by the gravitational condition. The high-gravity level can
effectively affect the phase composition and morphology of the products.
Commercial Applications: Some commercial applications of centrifuges are as follows:

3. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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 Standalone centrifuges for drying (hand-washed) clothes – usually with a water
outlet.
 Washing machines are designed to act as centrifuges to get rid of excess water in
laundry loads.
 In soil mechanics, centrifuges utilize centrifugal acceleration to match soil stresses
in a scale model to those found in reality.
 Large industrial centrifuges are commonly used in water and wastewater treatment
to dry sludges. The resulting dry product is often termed cake, and the water
leaving a centrifuge after most of the solids have been removed is called centrate.
 Large industrial centrifuges are also used in the oil industry to remove solids from
the drilling fluid.
 Centrifuges are used to separate cream (remove fat) from milk.