What is a Laboratory Centrifuge and How does it Work?
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
Types of Laboratory Centrifuges
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
Pelleting nucleic acids
Pelleting proteins from
Microfiltration of small
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.
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.
Analytical ultracentrifuges are capable of operating at 500,000g. Some of the optical
systems used in this system for analysis include:
The light absorption system
The alternative Schlieren
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
Laboratory Centrifuge Rotors
There are different types of rotors for
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
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:
Corrosion-free rotors - Most centrifuges used in
the lab and used for biological purposes. For this reason, it is better to fine
a centrifuge that comes with corrosion free rotors, which not only last longer,
but also do not contaminate the material. Today, carbon fiber composites are
being used for the rotors for better overall results.
Noise - A centrifuge will most
probably produce a lot of noise when in use. However, it is worth finding one
that has been designed to minimize the amount of noise produced.
Versatility - While different types of
centrifuges are used for different applications, it is worth checking out a
centrifuge that is general purpose in the event that the user does not need
Type of rotor - There are different
types of rotors used in centrifuges. When looking for a centrifuge, it is
important to know what type of rotor a given centrifuge uses depending on the
needs of the user.
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