Centrifuges
Counter Top Centrifuge
A Laboratory Centrifuge is a piece of laboratory equipment, driven by a motor, which spins liquid samples at high speed. There are two main sizes for laboratory centrifuges. The larger ones are known simply as centrifuges; samples are contained in Centrifuge Tubes or centrifuge tips. The smaller centrifuges are known as microcentrifuges or microfuges, and microcentrifuge tubes or microfuge tubes are used with them.
Like all other centrifuges, laboratory centrifuges work by the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density.
Increasing the effective gravitational force will more rapidly and completely cause the precipitate ("pellet") to gather on the bottom of the tube. The remaining solution is called the "supernate" or "supernatant".
The supernatant liquid is then either quickly decanted from the tube without disturbing the precipitate, or withdrawn with a Pasteur pipette. The rate of centrifugation is specified by the acceleration applied to the sample, typically measured in revolutions per minute (RPM) or g. 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 use of a centrifuge is known as centrifugation.
There are various types of centrifugation:
- Differential centrifugation, often used to separate certain organelles from whole cells for further analysis of specific parts of cells
- Isopycnic centrifugation, often used to isolate nucleic acids such as DNA
- Sucrose gradient centrifugation, often used to purify enveloped viruses and ribosomes, and also to separate cell organelles from crude cellular extracts