Cyclonic separation is a type of centrifugation. A high speed rotating airflow moves in a spiral pattern from the top of the cyclone to the bottom.
Larger particles in the rotating stream have too much inertia to follow the tight curve of the stream. They strike the outside wall and fall to the bottom for removal. In the home, bagless vacuum cleaners are cyclone separators in disguise. Sawmills use large-scale cyclones remove sawdust from extracted air. Oil refineries use them to separate oils and gases.
Centrifuges utilize glass or plastic tubes that fit in the rotor cavities. The size and type of the sample tubes influence the samples that can be used in the unit. For example, glass tubes can be used with the majority of solvents but are often more expensive.
Plastic tubes, when used with care, can be just as durable, however, water is the preferred solvent. 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, to 7,x 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.
Large capacity refrigerated centrifuges feature a refrigerated rotor chamber. They collect substances that sediment rapidly, similar to like small bench models, and with a maximum speed of 6, g. High-speed centrifuges are much like the large capacity models, except they can reach max speeds of about 60, g.
These models can collect larger cellular organelles, cellular debris, microorganisms, and proteins precipitated by ammonium sulfate. The refrigerated models can also feature a refrigerated rotor chamber. Ultra centrifuges are optimized to spin at very high speeds, capable of reaching as high as 1,, g 9, kilometers per second or 6, miles per second. These kinds of centrifuges are classified as either preparative or analytical.
Preparative ultracentrifuges reach about , g. They are used to determine the shape and mass of macromolecules, separate lipoprotein molecules from plasma, and a variety of other tasks. The centripetal acceleration essentially simulates higher gravity, however, it's important to keep in mind the artificial gravity is a range of values, depending 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. The types of centrifuges are all based on the same technique but differ in their applications. The main differences between them are the speed of rotation and the rotor design.
The rotor is the rotating unit in the device. Fixed-angle rotors hold samples at a constant angle, swinging head rotors have a hinge that allows sample vessels to swing outward as the rate of spin increases, and continuous tubular centrifuges have a single chamber rather than individual sample chambers.
Separating Molecules and Isotopes: Extremely high-speed centrifuges and ultracentrifuges spin at such high rates that they can be used to separate molecules of different masses or even isotopes of atoms.
Isotope separation is used for scientific research and to make nuclear fuel and nuclear weapons. For example, a gas centrifuge may be used to enrich uranium , as the heavier isotope is pulled outward more than the lighter one. In the Lab: Laboratory centrifuges also spin at high rates. They may be large enough to stand on a floor or small enough to rest on a counter. A typical device has a rotor with angled drilled holes to hold sample tubes.
Because the sample tubes are fixed at an angle and centrifugal force acts in the horizontal plane, particles move a tiny distance before hitting the wall of the tube, allowing dense material to slide down. While many lab centrifuges have fixed-angle rotors, swinging-bucket rotors are also common.
Such machines are employed to isolate components of immiscible liquids and suspensions. Uses include separating blood components, isolating DNA, and purifying chemical samples. 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. In ultrafiltration, macromolecules are purified, separated, and concentrated by using a membrane. Isopycnic centrifugation is carried out using a "self-generating" density gradient established through equilibrium sedimentation. This method concentrates the analysis matches with those of the surrounding solution. Protocols for centrifugation typically specify the relative centrifugal force rcf and the degree of acceleration in multiples of g g-force.
Working with the rotational speed, such as revolutions per minute rpm , is rather imprecise. In general, applications for centrifugation specify the degree of acceleration to be applied to the sample rather than specifying a specific rotational speed such as revolutions per minute. The distinction between rpm and rcf is important, as two rotors with different diameters running at the same rotational speed rpm will result in different accelerations rcf.
As the motion of the rotor is circular, the acceleration force is calculated as the product of the radius and the square of the angular velocity. As mentioned, when using rotors with different radii for centrifugation, the same rcf g-force should be used. Both centrifuges can spin a rotor with 1. To make life easier and to better reproduce the data, some centrifuges have buttons directly on the operating panel for automatic conversion between rpm and rcf.
If your centrifuge does not have an rpm-rcf converter, you may use the formula, the rpm-rcf converter found on the homepages of centrifuge suppliers, or a nomogram for conversion. The k-factor is a parameter for the sedimentation distance in a test tube. This factor is also called clearing factor and represents the relative pelleting efficiency of a centrifugation system at maximum rotational speed. In general, the k-factor value is used to estimate the time, t in hours , required for complete sedimentation of a sample fraction with a known sedimentation coefficient measured in s svedberg.
A small k-factor represents a more rapid separation.
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