laboratory equipment

1. CENTRIFUGATION
Centrifugation is a technique of separating components where the centrifugal
force/ acceleration causes the denser molecules to move towards the periphery
while the less dense particles move to the center.
Separation can also be done naturally through sedimentation.
Centrifugation is done using a Centrifuge
A centrifuge: is a device used to separate components of a mixture on the basis of their
size, density, the viscosity of the medium,
The particles to be separated are usually cells, subcellular organelles, or large
molecules

2. Principle of centrifugation
A centrifuge works by using the principle of sedimentation: Under
the influence of gravitational force (g-force), substances separate
according to their density. particles are concentrated as a pellet
at the bottom of the centrifuge tube and separated from the
remaining solution, called supernatant. During phase separation,
chemicals are converted from a matrix or an aqueous medium to
a solvent (for additional chemical or molecular biological
analysis).

3. The process of centrifugation relies on the perpendicular force
created when a sample is rotated about a fixed point.
Relative Centrifugal Force (RCF)
 Relative centrifugal force is the measure of the strength of rotors
of different types and sizes.
This is the force exerted on the contents of the rotor as a result of the
rotation.
Formula: RCF (g Force)= 1.118 × 10-5 × r × (RPM)2
where r is the radius of the rotor (in centimeters), and RPM is the speed of the
rotor in rotation per minute.

4. Parts of a basic centrifuge
Motor – Helps to drive a centrifuge
Control panel- for controlling centrifuge
operation
Chamber – houses entire centrifuge
Latch-Keeps the centrifuge closed (lock)
Rotor – House tubes with sample, they
generate speed that brings about
separation.

5. Types of Rotor
• Fixed angle rotor
• Vertical rotor
• Swinging bucket rotor
Fixed angle – tubes are held at an
angle of 20 – 45 Degrees to the
vertical , particles move radially
outwards
Vertical – tubes are held parallel
to the rotor axis
Swinging bucket – Swing out
horizontally when rotor
accelerates.

6. Factors influencing centrifugation:
 Density of both samples and solution
 Temperature/viscosity
 Distance of particles displacement
 Rotation speed
In a solution, particles whose density is higher than that of the
solvent sink (sediment), and particles that are lighter than it
float to the top. The greater the difference in density, the faster
they move. If there is no difference in density (isopyknic
conditions), the particles stay steady.

7. Types of centrifugation
1. Density gradient centrifugation
2. Differential centrifugation
3. Ultracentrifugation
1. Density gradient
Density gradient centrifugation is the separation of molecules where the separation is based on the
density of the molecules as they pass through a density gradient under a centrifugal force.
Principle
 Molecules continue to settle down under a centrifugal force until they reach a medium
with the density the same as theirs - The more dense molecules begin to move towards
the bottom as they move through the density gradient.
 The molecules then become suspended at a point in which the density of the particles
equals the surrounding medium.

8. 2. Differential centrifugation
Differential centrifugation is a type of centrifugation process in which components
are separately settled down a centrifuge tube by applying a series of increasing
centrifugal force.
Principle of Differential centrifugation
Differential centrifugation is based upon the differences in the sedimentation rate of
biological particles of different size and density.
As the increasing centrifugal force is applied, initial sedimentation of the larger
molecules takes place.
Further particles settle down depending upon the speed and time of individual
centrifugation steps and the density and relative size of the particles.

9. 3. Ultracentrifugation
Ultracentrifugation is a specialized technique
used to spin samples at exceptionally high
speeds (e.g 150 000 RPM)

10. • Two forces counteract the centrifugal force acting on the suspended particles:
Buoyant force: force with which the particles must displace the liquid media into which they
sediment.
Frictional force: force generated by the particles as they migrate through the solution.
Particles move away from the axis of rotation in a centrifugal field only when the centrifugal force
exceeds the counteracting buoyant and frictional forces resulting in sedimentation of the particles at a
constant rate.
TYPES OF CENTRIFUGES
Separations are a critical step in your workflow; thus it’s important to consider the centrifuge
requirements and technical specifications for your applications
Microcentrifuges - support all your micro volume protocols e.g hematocrit capillaries, PCR tubes
Small Benchtop Centrifuges - Mainly used for small amount of material that rapidly sediment like
yeast cells, erythrocytes used in microbiology, Chemistry, Microbiology, Hematology, Immunology
General Purpose Centrifuges – for benchtop use
Large Capacity Centrifuges - High‐throughput applications such as blood banking and
bioprocessing.