What is centrifugation? What is the method used for? The term "centrifugation" means the separation of liquid or solid particles of a substance into different fractions using centrifugal forces. Such separation of substances is carried out through the use of special apparatuses - centrifuges. What is the principle of the method?
Centrifugation principle
Consider the definition in more detail. Centrifugation is the effect on substances by ultra-high-speed rotation in a specialized apparatus. The main part of any centrifuge is the rotor, which contains slots for installing test tubes with material, which must be separated into separate fractions. During rotation of the rotor at elevated speeds, centrifugal force comes into play . Substances placed in test tubes are separated into various substances according to the density level. For example, when centrifuging groundwater samples, the liquid separates and the solids contained in it precipitate.
Method Author
For the first time it became known what centrifugation is, after the experiments conducted by the scientist A.F. Lebedev. The method was developed by the researcher to determine the composition of soil water. Previously, liquid settling was used for these purposes, followed by separation of solid samples from it. The development of a centrifugation method made it possible to cope with this task much faster. Thanks to this separation, it became possible to extract a solid fraction of substances from a liquid in a dry form within minutes.
Centrifugation Steps
Differential centrifugation begins with the sedimentation of substances that are subject to research. Such material processing takes place in settling apparatus. During sedimentation, particles of matter are separated under the influence of gravity. This allows you to prepare substances for better separation using centrifugal forces.
Subsequently, the substances in the test tubes are filtered. At this stage, the so-called perforated drums are used, which are intended to separate liquid particles from solid ones. During the measures presented, all the sediment remains on the walls of the centrifuge.
Method Advantages
Compared with other methods aimed at the separation of individual substances, such as filtration or sedimentation, centrifugation makes it possible to obtain a precipitate with a minimum moisture content. The use of this separation method allows the separation of finely divided suspensions. The result is a particle size of 5-10 microns. Another important advantage of centrifugation is the possibility of its implementation using equipment of small volumes and dimensions. The only drawback of the method is the high energy intensity of the devices.
Centrifugation in Biology
In biology, the separation of substances into separate substances is resorted to if necessary to prepare preparations for research under a microscope. Centrifugation is carried out on complex devices - cytotors. Such devices, in addition to slots for tubes, are equipped with sample holders, all kinds of slides of complex construction. When conducting research in biology, the quality of the materials obtained and, accordingly, the amount of useful information that can be gleaned from the results of the analysis directly depend on the centrifuge device.
Centrifugation in the oil refining industry
The centrifugation method is indispensable in oil production. There are hydrocarbon minerals from which water is not completely released during distillation. Centrifugation makes it possible to remove excess fluid from the oil, increasing its quality. In this case, the oil is dissolved in benzene, then heated to 60 ° C, and then subjected to centrifugal force. At the end, measure the amount of remaining water in the substance and, if necessary, repeat the procedure.
Blood centrifugation
This method is widely used for medicinal purposes. In medicine, it allows you to solve the following series of problems:
- Obtaining purified blood samples for plasmapheresis. For these purposes, in a centrifuge, the formed elements of blood are separated from its plasma. The operation makes it possible to rid the blood of viruses, excess antibodies, pathogenic bacteria, toxins.
- Blood preparation for donor transfusion. After separation of the body fluid into separate fractions by centrifugation, blood cells are returned to the donor, and the plasma is used for transfusion or frozen for subsequent use.
- Platelet mass. The substance is obtained from blood plasma enriched with platelets. The resulting mass is used in surgical and hematological departments of medical institutions, in emergency therapy, operating rooms. The use of platelet mass in medicine makes it possible to improve blood coagulation in victims.
- The synthesis of red blood cells. Centrifugation of blood cells occurs by delicate separation of its fractions according to a special technique. The finished mass rich in red blood cells is used for transfusion during blood loss, operations. The erythrocyte mass is often used to treat anemia and other systemic blood diseases.
In modern medical practice, many new generation devices are used that make it possible to accelerate a rotating drum to a certain speed and stop it at a certain moment. This allows you to more accurately divide the blood into red blood cells, platelets, plasma, serum and clots. In a similar way, other bodily fluids are examined, in particular, substances in the urine are separated.
Centrifuges: main types
We figured out what centrifugation is. Now let's find out which devices are used to implement the method. Centrifuges are closed and open, with mechanical or manual drive. The main working part of hand-held open devices is a rotating axis located vertically. In its upper part, a bar is fixed perpendicularly, where movable metal sleeves are located. They contain special tubes, narrowed at the bottom. Cotton wool is placed at the bottom of the sleeves, which avoids damage to the glass tube when it comes into contact with metal. Further, the apparatus is set in motion. After some time, the liquid is separated from the suspended solids. After this, the manual centrifuge is stopped. A dense, solid precipitate is concentrated at the bottom of the tubes. Above it is the liquid part of the substance.
Closed-type mechanical centrifuges have a large number of sleeves for tube placement. Such devices are more convenient than manual ones. Their rotors are driven by powerful electric motors and are able to accelerate to 3000 rpm. This makes it possible to carry out a better separation of liquid substances from solid.
Features of the preparation of tubes during centrifugation
The tubes used for centrifugation should be filled with the test material of identical mass. Therefore, special high-precision scales are used here for measurements. When balancing numerous tubes in a centrifuge is required, resort to the next step. After weighing a pair of glass containers and achieving the same mass, one of them is left as a reference. Subsequent tubes are equilibrated with this sample before being placed in the apparatus. This technique significantly speeds up the work if necessary to prepare for centrifugation of a series of tubes.
It is worth noting that in test tubes never put too much of the investigated substance. Glass containers are filled so that the distance to the edge is at least 10 mm. Otherwise, the substance will pour out of the tube under the influence of centrifugal force.
Supercentrifuge
The use of conventional manual or mechanical centrifuges is not sufficient to separate extremely thin suspensions. In this case, a more impressive impact on substances from centrifugal forces is required. When implementing such processes, supercentrifuges are used.
The devices of the presented plan are equipped with a deaf drum in the form of a tube of small diameter - not more than 240 mm. The length of such a drum significantly exceeds its cross section, which makes it possible to significantly increase the number of revolutions and create a powerful centrifugal force.
In a supercentrifuge, the test substance enters the drum, moves through the tube and hits special reflectors that throw material onto the walls of the device. There are also chambers designed for separate output of light and heavy liquids.
The advantages of supercentrifuges include:
- absolute tightness;
- highest intensity of separation of substances;
- compact sizes;
- the possibility of separation of substances at the molecular level.
Finally
So we found out what centrifugation is. Currently, the method finds its application when it is necessary to isolate precipitates of solutions, purify liquids, and separate components of biologically active and chemical substances. Ultracentrifuges are used to separate substances at the molecular level. The centrifugation method is actively used in the chemical, oil, nuclear, food industry, as well as in medicine.