Definition:
Centrifugation is a process involving the use of the centrifugal force for the sedimentation of heterogeneous mixtures with an instrument called a centrifuge, used in industry and in laboratories.
This process is used to separate two immiscible liquids.
More-dense components of the mixture migrate away from the axis of the centrifuge, while less dense components of the mixture migrate towards the axis.
Centrifuge is a device for separating particles from a solution according to their sizes, shapes, densities, and viscosities of the medium.
Applications of centrifugation:
Production of bulk drugs.
Production of biological products.
Biopharmaceutical analysis of drugs.
Evaluation of suspensions and emulsions.
Determination of molecular weight of colloids.
Theory of centrifugation:
The centrifuge works on sedimentation.
Spinning samples at a high speed.
The components of a mixture are subjected to centrifugal force, Dense particles migrate away from the axis of rotation and lighter ones move towards it.
Relative Centrifugal Force (RCF):
RCF is the ratio of the centrifugal acceleration at a specified radius and the speed to the standard acceleration of gravity.
Relative Centrifugal force is defined as
f=Mω2 r
Where,
F= intensity of centrifugal force
M= mass of particle
ω= angular velocity of rotation
R= distance of migrating particles from central axis of rotation.
The RCF value for any centrifuge may be calculated from the following equation:
RCF = 1.18 × r × (rpm) 2 ×10-5
Where,
1.18×10-5 = An empirical factor
r is the radius in cm from the center of the centrifuge shaft to the external tip of the centrifuge tube.
rpm is the number of revolutions per minute of the centrifuge rotor.
The time required to separate particles depends on the rotor speed, radius of rotor and effective path length traveled by sedimented particles.
The following formula is useful for the calculation of the speed required for a rotor with a radius that differs from the radius with which a prescribed,
R.P.M. = 1000× √RCF/1.18×r
The length of time of centrifugation also can be calculated so that running with an alternative rotor of a different size is equivalent to running with an original rotor.
Commonly Asked Questions.
Define “Centrifugation”? Give its applications in the Pharmacy,
Write a short note on theory of Centrifugation.