Centrifugation: Introduction.

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.

1. Define “Centrifugation”? Give its applications in the Pharmacy,

2. Write a short note on theory of Centrifugation.