A laboratory centrifuge is a motor-driven device used in laboratories for the purposes of separating the components of a liquids. Laboratory centrifuges are widely used in hospitals or other industries where they are used for extracting suspended material from a variety of medium. This is achieved through the sedimentation principle, where centripetal acceleration results in denser substances moving towards the radial direction.
As the device spins, a large force is created that causes denser substances in the liquid to start moving and eventually settle outward while the less dense move to the middle. Laboratory centrifuges vary in size and speed depending on intended use. While power is required to operate the device (cause it to spin) there are also various manually operated centrifuges that can simply work by rotating a lever.
* Substances are also separated based on their size, shape and viscosity
Microcentrifuges have a compact design and are typically used for small tubes of between 0.2 ml and 2.0 ml. Although they are mostly used for smaller tubes, some of these centrifuges come with a different rotor/rotor adaptors that can easily be switched in order to accommodate tubes of different size. A microcentrifuge is small, and thus has a smaller footprint. As such, it takes up little space on the working bench.
Microcentrifuges are typically used for the following purposes:
Refrigerated centrifuges are used for samples that need a consistent range of temperature. With such centrifuges therefore; it is essential that they run at maximum speeds while still maintaining a consistent temperature. For the most part, the temperature range of refrigerated centrifuges is between -20 and -40c. This range makes them ideal for the analysis of DNA, RNA, PCR and antibodies.
These centrifuges can also achieve speeds of over 30,000 rounds per minute with relative centrifugal force of over 65,000 x g. They may come in varying configurations such as the swing bucket, fixed angle or both. They are smaller (refrigerated microcentrifuges) and large capacity refrigerated centrifuges for different uses. A microcentrifuge (microfuge) is used for smaller samples (2ml or less) and are often used for biological applications. They come with varying speed range and different holding capacities (the number of tubes it can hold at a time).
On the other hand, large capacity refrigerated centrifuges have capacity to change rotor chambers with varying sizes. These types of centrifuges can go to a maximum of up to 65,000g. They are typically used for collecting substances that sediment rapidly such as yeast cells, chloroplast and erythrocytes.
* The chamber of refrigerated centrifuges are sealed to meet the conditions of the material.
High Speed Refrigerated Centrifuges
This is a type of refrigerated centrifuge that is capable of high speeds of up to 60,000g. As such, they can produce significant force that is used for the purposes of collecting cellular debris, micro-organisms as well as larger cell organelles and proteins.
High speed refrigerated centrifuges also come in varying sizes and holding capacities depending on the needs of the user.
This is a type of laboratory centrifuge that has been optimized for very high speeds. As such, they can generate accelerations of up to 1,000,000 g, which is about 9,800 km/s2. Unlike other types of centrifuges that offer lower rotation speeds, ultracentrifuges allows the user to take advantage of the tiny differences between such molecules as proteins and nucleic acids for the separation.
There are two types of ultracentrifuges which include;
This is a type of ultracentrifuge that offers relative centrifugal force of up to 600,000g. Preparative ultracentrifuges are mostly used to separate particles on the basis of their densities, isolation of denser particles for pellet collection as well as clarifying suspensions that contain particles. As such, they help separate macromolecules and lipoprotein fractions from plasma as well as deprotonisation of physiological fluids for the analysis of amino acids.
Depending on its application, a preparative ultracentrifuge can also be equipped with different types of rotor that spin different numbers of samples at different angles and speeds.
What sets this centrifuges apart from others is that they incorporate a scanning visible light based optical detection system which is used for real-time monitoring of samples as they spin. With this centrifuge, users have an opportunity to look at the sedimentation process and thus see the sample as it concentrates with increasing centrifugal force.
The Analytical ultracentrifuges are capable of operating at 500,000g. Some of the optical systems used in this system for analysis include:
Common analysis performed using these types of centrifuges include:
Sedimentation velocity experiments - Here the centrifuge, detector and computer record the time course of the process and provide information about the shape, mass and size of the sediments.
Sedimentation equilibrium experiments - This is used to study the steady state equilibrium of the sample in the solution. Here, the sample continues to exist in steady state equilibrium even after sedimentation is completed. This type of analysis provides information about mass and chemical equilibrium constants.
There are different types of rotors for different centrifuges.
Swinging bucket rotors- With this rotor, there are buckets (that hold tubes) that rest in the vertical position (when not in use) but swing out in a horizontal position when acceleration start.
Fixed angle rotors - Here, the rotor body is set at an angle of between 14 degrees and 40 degrees on the vertical.
Vertical tube rotors - Here, the tubes are vertically aligned in the body of the rotors at all times (even during rotation)
Elutriator rotors - This is a type of rotor that contain recesses for holding a single conical shaped separation chamber. Here, the apex points away from the axis of rotation while a bypass chamber serves as a counter balance for fluid outlet.
When considering purchasing of centrifuge, some of the most important things to look out for include:
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