The term “centrifuge” can refer to a machine (noun) or the act of using a machine (verb) that holds a rapidly spinning container to separate its contents by density. Centrifuges are most commonly used to separate different liquid and solid particles from liquids. But they can also be used for gases, and used for purposes other than mechanical separation.
Some of the most common applications for centrifuges include separation, purification and separation of organelles, cells and cellular components and more complex mixtures of nucleic acids, proteins and viruses for further observation. Hence the subsequent increase in demand for virus research leading to several developments in centrifugation techniques. Eventually led to the commercial centrifuge as we know it now.
Invention and Early History of The Centrifuge
The origin of the modern centrifuge can be traced back to the rotating arm device designed by British military engineer Benjamin Robbins to measure resistance in the 18th century. In 1864, Antonin Prandtl applied this technique to separate the components of milk and cream. In 1875, Plant’s brother Alexander, improved the technique, inventing a machine to extract milk fat. Although centrifuges are still used to separate milk components. But their use has expanded into many other fields of science and medicine.
Uses and Types of Centrifuges
The types of centrifuges are all based on the same technology. But their applications are different. The main difference between them is the rotational speed and rotor design. The rotor is the rotating unit in the device. The fixed angle rotor holds the sample at a constant angle. The swing head rotor has a hinge that allows the sample container to swing outward as the rotation rate increases. Continuous tube centrifuges have a separate chamber instead of a separate sample chamber.
In the laboratory: The laboratory centrifuge also spins at high speed. They may be large enough to stand on the floor or small enough to put on a counter. A typical setup has a rotor with angled holes to hold the sample tube. Since the sample tube is fixed at an angle and centrifugal force acts on the horizontal plane. So the particles travel a short distance before hitting the tube wall, allowing the dense material to slide down. While many laboratory centrifuges have fixed angle rotors, swinging barrel rotors are also common. Such machines are used to separate the components of immiscible liquids and suspensions. Uses include separating blood components, isolating DNA, and purifying chemical samples.
Separating molecules and isotopes: Ultracentrifuges and ultracentrifuges spin at high speeds, and they can be used to separate molecules of different masses, even isotopes of atoms. Isotope separation is used in scientific research and in the manufacture of nuclear fuel and nuclear weapons. For example, gas centrifuges can be used to enrich uranium (because heavier isotopes are more likely to be pulled outwards than lighter ones).
Industrial Centrifuges are used to separate components of colloids (like cream and butter from milk), in chemical preparation, cleaning solids from drilling fluid, drying materials, and water treatment to remove sludge. Some industrial centrifuges rely on sedimentation for separation, while others separate matter using a screen or filter. Industrial centrifuges are used to cast metals and prepare chemicals. The differential gravity affects the phase composition and other properties of the materials.
High-Gravity Simulation: Large centrifuges may be used to simulate high-gravity. The machines are the size of a room or building. Human centrifuges are used to train test pilots and conduct gravity-related scientific research. Centrifuges may also be used as amusement park rides. While human centrifuges are designed to go up to 10 or 12 gravities, large-diameter non-human machines can expose specimens to up to 20 times normal gravity. The same principle may one day be used to simulate gravity in space.
Large capacity refrigerated centrifuges feature a refrigerated rotor chamber. It’s possible to change rotor chambers to accommodate another size. They collect substances that sediment rapidly, similar to like small bench models, and with a maximum speed of 6,500 g.
Ultra centrifuges are optimized to spin at very high speeds, capable of reaching as high as 1,000,000 g (9,800 kilometers per second or 6,089 miles per second). These kinds of centrifuges are classified as either preparative or analytical.
Small Bench Centrifuges : Also known as benchtop centrifuges, these collect small amounts of material such as yeast cells and erythrocytes. Small bench centrifuges have a maximum relative centrifugal field of 3,000 to 7,000x the force of gravity, known as gravitational force or g-force (g).
Compared to other options, these are relatively low speed. These are a general-purpose centrifuge and are among the most affordable options available today.
Preparative ultracentrifuges reach about 600,000 g. They are used to determine the shape and mass of macromolecules, separate lipoprotein molecules from plasma, and a variety of other tasks. Preparative ultracentrifuges feature chambers that are refrigerated, sealed, and evacuated.
With an analytical ultracentrifuge, there are three optical systems to choose from: a light absorption system, the Schlieren system, and the Rayleigh interferometric system.
The Schlieren and Rayleigh systems are used to detect changes in the refractive index of the solution, whereas a light absorption system detects changes via ultraviolet light absorption. These models run at about 500,000 g.
Everyday Applications: Medium-size centrifuges are common in daily life, mainly to quickly separate liquids from solids. Washing machines use centrifugation during the spin cycle to separate water from laundry. A similar device spins the water out of swimsuits. Salad spinners, used to wash and then spin dry lettuce and other greens, are another example of a simple centrifuge.
Types of Centrifuge Rotors
Beyond the type of centrifuge itself, it’s also important to consider the centrifuge rotor, as the rotor design influences what the machine can do and how much it costs.
Fixed Angle Rotors
Fixed Angle Rotors: With this rotor design, the sample types are held at a constant fixed angle – one that falls anywhere between 14 and 40. The relative centrifugal force means the particles have to move outward and collide with the outer wall of the centrifuge tube.
Swinging Bucket Rotors
These rotors feature buckets that start in a vertical position and swing into a horizontal position during acceleration. The tube and its solution are aligned parallel to the centrifugal field and perpendicular to the axis of rotation.
A region of higher concentration is formed, and this area has a greater density than the surrounding medium. The precipitate collects as a compact pellet at the outermost point of the tube.
There aren’t nearly as many applications that require specialized rotors like continuous-flow rotors or drum rotors compared to fixed angle or swinging bucket rotors. But, when it is needed, you see how important continuous flow really is.
It is considered a time-saver, making efficient work of separating large volumes of materials at high centrifugal forces without the repetitiveness of filling and decanting dozens of centrifuge test tubes or frequently starting and stopping the rotor.
Flow rotors are best suited for applications such as processing cell and algae harvest, mitochondria, large viruses, bacteria, and tissue homogenates.
How Does a Centrifuge Work
Centrifuges get their name from centrifugal force—the virtual force that pulls spinning objects outward. Centripetal force is the physical force that actually works, pulling a spinning object inward. Spinning a bucket of water is a good example of these forces at work.
If the bucket spins fast enough, the water will be pulled inward and not overflow. If the bucket is filled with a mixture of sand and water, spinning it creates a centrifugal effect. According to the principle of settlement, both water and sand in the bucket are attracted to the outer rim of the bucket. But dense sand grains settle to the bottom, while lighter water molecules shift toward the center.
Centripetal acceleration basically simulates higher gravity. However, it’s important to remember that artificial gravity is a range of values that depends on how close an object is to the axis of rotation, not a constant value. The effect is greater the further out an object gets because it travels a greater distance for each rotation.
How Much Is a Centrifuge
Centrifuge costs vary widely depending on the size, type, and features of the unit. Average prices by type are:
Benchtop – $1,000 to $5,000
Large Capacity / High Speed – $10,000 to $25,000
Ultracentrifuge – $10,000 to $50,000
Adding refrigeration to any of the centrifuges will cause the price to be higher. Customization along with the option to purchase additional rotors also increases the cost.
Buying a centrifuge means investing a considerable amount of capital upfront, depending on the number of units you need, the type of centrifuge, and the add-ons and customizations your lab needs.
So explore our selection of centrifuge or submit a custom quote request for the perfect centrifuge for your needs. For more information about custom and standard centrifuge from KETHINK, contact us.