Centrifugation
Ondiano, Eliza L.
MSEST – 1 CENTRIFUGATION
Centrifugation is a process which through rapid spinning imposes high sustained centrifugal force on suspended particles, or even molecules in solution, and causes separations of such matter on the basis of differences in densities. 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. Effectively, the centrifuge substitutes a similar, stronger force for that of gravity. The precipitate or pellet is the particle that gathers on the bottom of the tube, while the remaining solution is the supernate or supernatant liquid.
The part of the centrifuge that holds the centrifugation tubes is called the centrifuge rotor. Centrifuges are designed so that a number of different rotors can be used by the instrument. There are three types of centrifuge rotors: fixed angle rotors, swinging bucket rotors, and vertical rotors. Fixed-angle and swinging-bucket rotors are the most commonly used. In a fixed-angle rotor, the centrifuge tubes are spun at a fixed angle, which is usually approximately 35 degress. Fixed angle rotors are most commonly used for pelleting cells and subcellular components. With swinging-bucket rotors, the tubes are free to swingout perpendicular to the axis of rotation as the rotor rotates. This rotor is particularly useful in density-gradient centrifugation schemes.
The rate of centrifugation is specified by the angular velocity measured in revolutions per minute (RPM), or acceleration expressed as g. The conversion factor between RPM and g depends on the radius of the sample in the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity.
The smaller the diameter of a centrifuge, the greater the forces and
MSEST – 1 CENTRIFUGATION
Centrifugation is a process which through rapid spinning imposes high sustained centrifugal force on suspended particles, or even molecules in solution, and causes separations of such matter on the basis of differences in densities. 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. Effectively, the centrifuge substitutes a similar, stronger force for that of gravity. The precipitate or pellet is the particle that gathers on the bottom of the tube, while the remaining solution is the supernate or supernatant liquid.
The part of the centrifuge that holds the centrifugation tubes is called the centrifuge rotor. Centrifuges are designed so that a number of different rotors can be used by the instrument. There are three types of centrifuge rotors: fixed angle rotors, swinging bucket rotors, and vertical rotors. Fixed-angle and swinging-bucket rotors are the most commonly used. In a fixed-angle rotor, the centrifuge tubes are spun at a fixed angle, which is usually approximately 35 degress. Fixed angle rotors are most commonly used for pelleting cells and subcellular components. With swinging-bucket rotors, the tubes are free to swingout perpendicular to the axis of rotation as the rotor rotates. This rotor is particularly useful in density-gradient centrifugation schemes.
The rate of centrifugation is specified by the angular velocity measured in revolutions per minute (RPM), or acceleration expressed as g. The conversion factor between RPM and g depends on the radius of the sample in the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity.
The smaller the diameter of a centrifuge, the greater the forces and