Introduction

A centrifuge is a machine that separates a fluid into its component parts. The operating principle of the centrifuge is based on a motor spinning a drum at high speed. Centrifugal force throws the fluid sample away from the centre and the heaviest particles travel the farthest.

centruge-principle-of-operation

Scientists can harness this characteristic on a practical level for example to remove solids or contaminants from liquids. They use it in the laboratory to separate immiscible liquids as well as isolating suspensions. Centrifuges are common in the fields of chemistry, biochemistry and biology. They can operate across a wide range of speeds and sizes. Sizes range from small bench-mounted units to units capable of coping with large volumes.

The sphere of clinical medicine also uses centrifuges for separating blood into cells, proteins and serum and for analyzing DNA. We can remove blood and contamination by spinning the DNA sample a few times, leaving only the raw DNA component.

Many commercial, industrial and of course scientific applications such as biological research facilities use centrifuges. The following are different types of centrifuge used in biological research with a summary of each of their uses.

Microcentrifuges

Microcentrifuges are small portable table-top machines that can run at very high speeds. They typically analyze very small samples of 2 milliliters or less. High-speed microcentrifuges can reach speeds of up to 35000rpm and 30000 times gravity. Microcentrifuges are generally located in scientific research laboratories. However their small size and portability means that they are also used in cold rooms and are refrigerated if required. They are ideally suited for subjecting very small quantities of cells, nuclei or molecules to short bursts of high levels of centrifugal force.

Low-speed centrifuges

Low-speed centrifuges range in size from bench top portable versions to self contained floor standing machines. Typical rotation speeds are less than 10000rpm. Uses include the harvesting of animal and plant cells, nuclei and chemical precipitates.

High-speed centrifuges

High-speed centrifuges deal with larger sample volumes up to several litres. Typically samples are in test tubes or bottles fixed to the rotors. Alternatively, in the case of more basic pelleting, fixed angled rotors. Uses include the harvesting of mitochondria, viruses and tubular membranes.

In addition to these, there are several less widely-used types of centrifuge:

Ultracentrifuges reach speeds of 150000rpm or to put it another way, a million times gravity force. Ultracentrifuges are capable of isolating particles which are far smaller and separating molecules in batch systems. Chemists also use ultracentrifuges for the density-gradient purification of particles