Laboratory Centrifuges. Theodor Svedberg. Centrifugation. 1. Introduction: Centrifugation is a technique in which solutes are separated by their different rate of travel (or sedimentation) in a centrifugal field. 2. Centrifugation is widely used in
1. Introduction: Centrifugation is a technique in which solutes are separated
by their different rate of travel (or sedimentation) in a centrifugal field.
2. Centrifugation is widely used in
The solutes are usually cells,
Sub- cellular organelles,viruses, large
molecules such as proteins & nucleic
Principles of centrifugation :
A centrifuge is a device for
separating particles from a solution
according to their size, shape,
density, viscosity of the medium
and rotor 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 hover. To take advantage of even tiny differences in density to separate various particles in a solution, gravity can be replaced with the much more powerful
“centrifugal force” provided by a centrifuge.
Type 1: Analytical Centrifugation : Applications: Measure the shape or mass of super molecular molecules
Type 2: Preparative Centrifugation : Application: Separation of cell, sub cellular structure, membrane vesicles
Generally spoken, there are two main types of rotors:
radius and the square of the angular velocity and it is traditionally named
"relative centrifugal force" (RCF).
For a spherical solute: of the solvent
S = 2/9 r2(d-do)/h
S is the sedimentation coefficient and is usually expressed in Svedbergs (S) or 10-13 sec.
r: radius of the solute, d: density of the solute, d0: density of media, and h :viscosity of the media.
Sedimentation coefficients of two solutes
in a centrifugal field.
2. Theory of centrifugation
Sedimentation rate of solutes is determined by their size, shape, and density, and the density and viscosity of media. The ability of an solute to centrifugal (or gravitational) field can be described by sedimentation coefficient (S = v/C): v linear velocity of a solute, C: centrifugal acceleration.
Three microcentrifuge tubes: 2 mL, 1.5 mL and 200 μL (for PCR).
Four screw-top micro-centrifuge tubes.