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 using centrifugal forces. This separation of substances is carried out through the use of special apparatus - centrifuges. What is the principle of the method?
Centrifugation principle
Let's consider the definition in more detail. Centrifugation is the impact 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 that is to 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 separated into different substances according to the level of density. For example, centrifuging groundwater samples separates the liquid and precipitates the solids it contains.
Authormethod
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 a researcher to determine the composition of soil water. Previously, liquid settling followed by separation of solid samples from it was used for this purpose. The development of the centrifugation method made it possible to cope with this task much faster. Thanks to this separation, it became possible to extract the solid fraction of substances from the liquid in dry form in a matter of minutes.
Steps of centrifugation
Differential centrifugation begins with the settling of substances that are to be investigated. Such processing of the material takes place in settling tanks. During settling, particles of matter are separated under the influence of gravity. This allows substances to be prepared for better separation using centrifugal forces.
Further, the substances in the test tubes are filtered. At this stage, the so-called perforated drums are used, which are designed to separate liquid particles from solid ones. In the course of the activities presented, all the sediment remains on the walls of the centrifuge.
Method advantages
Compared to other methods for separating individual substances, such as filtration or settling, centrifugation makes it possible to obtain a precipitate with a minimum moisture content. The use of this separation method makes it possible to separate finely dispersed suspensions. The result isobtaining particles with a 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 consumption of devices.
Centrifugation in biology
In biology, the separation of substances into separate substances is used when it is necessary to prepare preparations for examination under a microscope. Centrifugation here is carried out on complex devices - cytorotors. Such devices, in addition to slots for test tubes, are equipped with sample holders, all kinds of glass slides of a complex design. The quality of the obtained materials and, accordingly, the amount of useful information that can be gleaned from the results of the analysis directly depends on the design of the centrifuge when conducting research in biology.
Centrifugation in the oil refining industry
The centrifugation method is indispensable in oil production. There are hydrocarbon fossils from which water is not completely released during distillation. Centrifugation makes it possible to remove excess liquid from the composition of the oil, increasing its quality. In this case, the oil is dissolved in benzene, then heated to 60 oC, and then subjected to centrifugal force. Finally, measure the amount of remaining water in the substance and, if necessary, repeat the procedure.
Blood centrifugation
This method is widely used for medicalgoals. In medicine, it allows you to solve the following number of problems:
- Obtaining purified blood samples for plasmapheresis. For these purposes, blood cells are separated from its plasma in a centrifuge. The operation makes it possible to rid the blood of viruses, excess antibodies, pathogenic bacteria, toxins.
- Preparing blood for a donor transfusion. After separating the body fluid into separate fractions by centrifugation, the blood cells are returned to the donor, and the plasma is used for transfusion or frozen for later use.
- Isolation of 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 clotting in victims.
- Synthesis of erythrocyte mass. Centrifugation of blood cells occurs by delicate separation of its fractions according to a special technique. The finished mass, rich in erythrocytes, is used for transfusion in case of blood loss, operations. Erythrocyte mass is often used to treat anemia and other systemic blood diseases.
In modern medical practice, many devices of a new generation are used, which 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 separate blood into red blood cells, platelets, plasma, serum andclots. Other bodily fluids are examined in a similar way, in particular, substances in the composition of urine are separated.
Centrifuges: main types
We figured out what centrifugation is. Now let's find out what devices are used to implement the method. Centrifuges are either closed or open, with a mechanical or manual drive. The main working part of manual open devices is a rotating axis located vertically. In its upper part, a bar is perpendicularly fixed, where movable metal sleeves are located. They contain special test tubes, narrowed at the bottom. Cotton wool is placed at the bottom of the sleeves, which makes it possible to avoid damage to the glass test tube in contact with metal. Next, the apparatus is set in motion. After some time, the liquid is separated from the suspended solids. After that, the manual centrifuge is stopped. A dense, solid precipitate is concentrated at the bottom of the test tubes. Above it is the liquid part of the substance.
Mechanical closed type centrifuges have a large number of sleeves to accommodate test tubes. Such devices are more convenient than manual ones. Their rotors are driven by powerful electric motors and are capable of accelerating up to 3000 rpm. This makes it possible to carry out better separation of liquid substances from solid ones.
Features of tube preparation during centrifugation
Tubes that are used forcentrifugation, must be filled with test material of identical mass. Therefore, special high-precision scales are used for measurements here. When balancing multiple tubes in a centrifuge is required, the following technique is used. After weighing a pair 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 technique significantly speeds up the work if it is necessary to prepare a whole series of tubes for centrifugation.
It is worth noting that too much of the test substance is never placed in test tubes. Glass containers are filled in such a way that the distance to the edge is at least 10 mm. Otherwise, the substance will pour out of the test tube under the influence of centrifugal force.
Supercentrifuges
To separate the constituents of extremely fine suspensions, conventional manual or mechanical centrifuges are not enough. In this case, a more impressive effect on substances from centrifugal forces is required. Supercentrifuges are used in the implementation of such processes.
The devices of the presented plan are equipped with a blind drum in the form of a tube of small diameter - no 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 the supercentrifuge, the test substance enters the drum, moves along the tube and hits special reflectors that are thrown awaymaterial on the walls of the device. There are also chambers designed for separate withdrawal of light and heavy liquids.
Supercentrifuge benefits include:
- absolute tightness;
- highest separation rate;
- compact size;
- possibility of separating substances at the molecular level.
In closing
So we found out what centrifugation is. At present, the method finds its application when it is necessary to isolate sediments 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 industries, as well as in medicine.
