Search
What is a centrifuge?
A laboratory centrifuge is a device used to separate components of a sample based on the components’ densities by spinning them at high speeds. The centrifugal force generated by the rotation causes denser particles to move outward to the bottom or sides of the container, while less dense components remain closer to the center. This process is commonly used in biological and chemical laboratories for applications such as isolating cells, subcellular organelles, viruses, proteins, and nucleic acids.
Basic Principles
The basic principles of a centrifuge are centered around the use of centrifugal force to separate components of a mixture based on their densities.
The same physical principle of centrifugal force is also used in a washing machine. The washing machine uses centrifugal force to remove water from clothes during the spin cycle. They run usually between 600 and 1400 RPM (revolutions per minute), whereas centrifuges run from a few thousand RPM to over 100,000 RPM in ultracentrifuges.
Centrifugal Force:
- When a centrifuge spins, it generates a force perpendicular to the axis of rotation, pushing particles outward from the center of rotation.
- The centrifugal force (Fc) can be expressed as:
Fc=m⋅ω2⋅r
where m is the mass of the particle, ω is the angular velocity (in radians per second), and r is the radius of rotation.
Sedimentation:
- Particles suspended in a liquid will settle at different rates depending on their size, shape, and density when subjected to centrifugal force.
- Denser particles move outward faster and settle at the bottom of the centrifuge tube, while lighter particles remain closer to the top.
Relative Centrifugal Force (RCF):
- The effectiveness of a centrifuge in separating particles is often described by the relative centrifugal force (RCF), also known as the g-force.
History: Who invented centrifuges?
The invention of the centrifuge is attributed to Antonin Prandtl, a German dairy scientist, who developed the first practical centrifuge in 1864. His device was used to separate cream from milk. Later, his brother, Alexander Prandtl, improved upon the design, making it more efficient and practical for broader applications.
What types of centrifuges exist?
There are several types of laboratory centrifuges, each designed for specific applications and varying in size, speed, and capacity. The main types include:
Microcentrifuges:
- Used for small-volume samples (typically 0.5 to 2 mL tubes).
- Commonly used in molecular biology and biochemistry labs.
Benchtop Centrifuges:
- Versatile and used for a variety of routine laboratory applications.
- Accommodate larger volumes (up to 50 mL tubes) and have moderate speeds.
High-Speed Centrifuges:
- Capable of higher speeds (up to around 25,000 x g).
- Used for separating smaller particles and subcellular components.
Superspeed and Ultracentrifuges:
- Operate at extremely high speeds (Superspeed up to 100,000 x g, Ultraspeed up to 1,000,000 x g).
- Used for separating very small particles, such as viruses and ribosomes.
- Often used in molecular biology, biochemistry, and nanotechnology.
Refrigerated Centrifuges:
- Equipped with cooling systems to maintain low temperatures during operation.
- Essential for temperature-sensitive samples, such as proteins and live cells.
Clinical Centrifuges:
- Designed for use in medical laboratories.
- Commonly used for blood and urine sample processing.
Industrial Centrifuges:
- Designed for large-scale separation processes.
- Used in industrial applications and large-scale biological separations.
Each type of centrifuge serves distinct purposes and is chosen based on the specific requirements of the laboratory and the nature of the samples being processed.
How important is the centrifuge rotor?
A centrifuge rotor is a key component of a centrifuge that holds the sample tubes or containers and spins them at specific speeds to generate centrifugal force. The choice of rotor is crucial for achieving efficient and effective separation of samples, and it depends on several factors related to the application and sample properties.
What are other centrifuge components?
Centrifuge systems require specific components beyond the main unit to accommodate various research needs.
Different tube sizes and styles may necessitate different rotors or versatile rotors with appropriate adapters. There are
two primary rotor types: swinging bucket and fixed angle. A swinging bucket rotor consists of a rotor cross with
buckets that pivot to a horizontal position during centrifugation, and typically requires adapters to hold different tube
sizes. Optional bucket lids offer biocontainment. Fixed angle rotors have cavities molded at a specific angle (typically
45°) that hold tubes stationary during centrifugation, forming pellets along the side walls. These rotors usually include
a lid and can accommodate specialized adapters for smaller sample formats. When purchasing a centrifuge, it's
important to consider that while smaller benchtop models often include rotors, larger general purpose or
floor-standing centrifuges are sold without the rotor. Some manufacturers offer dedicated application packages that
include all necessary components.
Intended use of the products mentioned on this page vary. For specific intended use statements please refer to the product label.