What is centrifugation? Definition and principle of the method

What is centrifugation? What is the method used for? The term "centrifugation" means the separation of liquid or solid particles of a substance into various fractions by centrifugal forces. Such separation of substances is carried out due to the use of special apparatuses - centrifuges. What is the principle of the method?

Principle of centrifugation

Let's 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 nests for the installation of test tubes with material, which must be separated into separate fractions. During the rotation of the rotor at high speeds, centrifugal force comes into play . Substances placed in test tubes are divided into different substances according to the density level. For example, in the centrifugation of groundwater samples, liquid is separated and solids contained in it are deposited.

Author of the method

For the first time it became known that such a centrifugation, after the experiments conducted by the scientist A. F. Lebedev. The method was developed by the researcher in order to determine the composition of soil water. Earlier, for this purpose, liquid sedimentation was used, followed by the separation of solid samples from it. The development of the centrifugation method made it possible to cope with this task much more quickly. Thanks to this separation, it became possible to extract a solid fraction of substances from the liquid in a dry form for a few minutes.

Stages of centrifugation

Differential centrifugation begins with the uptake of substances that are subject to investigation. Such material processing takes place in the settling apparatus. During sedimentation, particles are separated by gravity. This allows you to prepare the substances for a better separation with the help of centrifugal forces.

Then the substances in the test tubes are filtered. At this stage, the so-called perforated drums are used that are intended to separate liquid particles from solids. During the submitted activities, the entire sediment remains on the walls of the centrifuge.

Advantages

Compared with other methods aimed at separation of individual substances, such as filtration or settling, centrifugation makes it possible to obtain a sediment with a minimum moisture content. The use of this separation method allows the separation of finely dispersed suspensions. The result is the production of particles 5-10 μm in size. Another important advantage of centrifugation is the possibility of its implementation with the help of 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 when preparing preparations for the study under a microscope. Centrifugation here is performed on complex devices - cytorotors. Such apparatuses besides the slots for test tubes are completed with sample holders, with all kinds of slides of a complicated design. From the device of the centrifuge, when conducting research in biology, the quality of the materials obtained directly depends on the amount of useful information that can be obtained from the analysis results.

Centrifugation in the oil refining industry

The method of centrifugation is indispensable in the extraction of oil. There are hydrocarbons, of which water is not fully emitted during distillation. Centrifuging makes it possible to remove excess liquid from the composition of oil, increasing its quality. In this case, the oil is dissolved in benzene, then heated to 60 ^° C, and then subjected to centrifugal force. Finally, the amount of water remaining in the substance is measured and, if necessary, the procedure is repeated.

Centrifugation of blood

This method is widely used for therapeutic purposes. In medicine, it allows you to solve the following problems:

1. Obtaining purified blood samples for plasmapheresis. For these purposes, the centrifuge separates the blood elements from its plasma. The operation makes it possible to rid the blood of viruses, excess antibodies, pathogenic bacteria, toxins.
2. Preparation of blood for donor transfusion. After separation of the body liquid into separate fractions by means of centrifugation, the blood donor is returned to the donor, and the plasma is used for transfusion or frozen for subsequent use.
3. Isolation of platelet mass. 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 coagulability in the affected.
4. Synthesis of erythrocyte mass. Centrifugation of blood cells occurs by delicate separation of its fractions according to a special technique. A ready mass, rich in red blood cells, is used for transfusion with blood loss, operations. Erythrocytic mass is often used for the treatment of anemia, other blood diseases of a systemic nature.

In modern medical practice, many new-generation instruments are used that allow the rotating drum to be accelerated 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. Similarly, other body fluids are examined, in particular, substances in the urine are separated.

Centrifuges: basic 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 a mechanical or manual drive. The main working part of the hand open devices is a rotating axis, located vertically. In its upper part the strip is fixed perpendicularly, where movable metal sleeves are located. They contain special test tubes, narrowed at the bottom. At the bottom of the sleeves lay cotton wool, which avoids damage to the glass tube when it comes into contact with the metal. Then the apparatus is set in motion. After a certain time, the liquid separates 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.

Mechanical closed 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 can accelerate to 3000 rpm. This makes it possible to carry out a better separation of liquid substances from solid substances.

Features of preparation of test 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 for measurements here. When the balancing of multiple test tubes in a centrifuge is required, the following method is used. After weighing a couple of glass containers and achieving the same mass, one of them is left as a standard. Subsequent tubes are equilibrated with this sample before being placed in the apparatus. This method significantly speeds up the work when it is necessary to prepare for centrifugation of a whole series of test tubes.

It is worth noting that there are never too many test substances in test tubes. The glass containers are filled in such a way that the distance to the edge is not less than 10 mm. Otherwise, the substance will pour out of the tube under the influence of centrifugal force.

Supercentrifuges

To separate the components of extremely thin suspensions, it is not sufficient to use conventional manual or mechanical centrifuges. In this case, a more impressive effect on the substances from the side of the centrifugal forces is required. When implementing such processes, supercentrifuges are used.

The devices of the presented plan are equipped with a blind drum in the form of a tube of insignificant diameter - no more than 240 mm. The length of such a drum is much larger than its cross section, which makes it possible to significantly increase the number of revolutions and create a powerful centrifugal force.

In the supercentrifuge, the test substance enters the drum, moves along the tube and strikes against special reflectors, which throws the material onto the walls of the device. There are also chambers designed for separate extraction of light and heavy liquids.

Advantages of supercentrifuges include:

• Absolute tightness;
• The highest intensity of separation of substances;
• Compact size;
• The possibility of separating substances at the molecular level.

Finally

So we found out what is centrifugation. Currently, the method finds its application when it is necessary to precipitate solutions of solutions, purify liquids, separate components of biologically active and chemical substances. Ultracentrifuges are used for the separation of substances at the molecular level. The method of centrifugation is actively used in the chemical, oil, nuclear, food industries, as well as in medicine.