A centrifuge is a special instrument that separates and precipitates a mixture (containing solids) by centrifugal force. Commonly used electric centrifuges in the laboratory include low-speed, high-speed centrifuges and low-speed, high-speed refrigerated centrifuges, as well as overspeed analysis and preparation of dual-purpose refrigerated centrifuges. Among them, low-speed (including large-capacity) centrifuges and high-speed refrigerated centrifuges are the most widely used, and are essential tools for biochemical laboratories to separate and prepare biomacromolecules. In the course of the experiment, in order to separate the precipitate from the mother liquor, both filtration and centrifugation are often used. However, the use of the centrifugation method is effective in the following cases.
1 The precipitate is sticky or the mother liquor is thick.
2 The precipitated particles are small and easy to pass through the filter paper.
3 The amount of precipitation is too much and loose.
4 The amount of precipitation is small and needs to be quantitatively determined. Or the amount of mother liquor is small, and the loss should be reduced when separating.
5 Precipitate and mother liquor must be separated quickly.
6 general colloidal solution.
1. Basic structure and performance of electric centrifuge
1 ordinary (non-frozen) centrifuge
This type of centrifuge has a simple structure and can be divided into two types: small mini centrifuge table and floor type. It is equipped with a drive motor, governor, timer and other devices, which is easy to operate. The speed of a low-speed centrifuge generally does not exceed 4000 rpm, and the maximum speed of a desktop high-speed centrifuge can reach 18,000 rpm.
2 low speed refrigerated centrifuge
The rotation speed is generally not more than 4000 rpm, and the maximum capacity is 2-4L. It is the most commonly used in the laboratory for the extraction of biological macromolecules and sediments. The rotor is mostly made of aluminum alloy, flat and angled. The centrifuge tube has various types of hard glass, polyethylene hard plastic and stainless steel tube. The centrifuge is equipped with a drive motor, timer, adjuster (speed indication) and refrigeration system (temperature adjustable range -20-+40 °C), which can be changed according to the needs of centrifugal materials. .
3 high speed refrigerated centrifuge
The rotational speed can reach above 20,000 rpm. In addition to the performance and structure of the low-speed refrigerated centrifuge, the angle rotor used in the high-speed centrifuge is made of titanium alloy and aluminum alloy. The centrifuge tube is a polyethylene hard plastic product with a cover. Such centrifuges are often used to collect microorganisms, cell debris, cells, large organelles, sulfate precipitates, and immunoprecipitates.
4 ultracentrifuge
The rotation speed can reach 50,000 rpm or more, and the subcellular organelle can be fractionated and used for the measurement of the molecular weight of proteins and nucleic acids. The rotor is made of high-strength titanium alloy, and can be replaced with different capacity and different types of speed rotors as needed. There are two types of ultracentrifuge drive motors, one for the FM motor to directly increase the speed, and the other for the speed through the gearbox. In order to prevent the drive motor from generating heat during high-speed operation, it is equipped with a cooling drive motor system (air-cooled, water-cooled), a speed limiter, a chronograph, a speed recorder, and the like. In addition, the ultracentrifuge is equipped with an evacuation system.
2. Precautions for use
(1) Usually, the centrifuge will have a registration form. Please register the user, the turntable, the speed and time before use.
(2) The centrifuge tube must be well balanced. Pay attention to the position balance when placing the centrifuge. Never exceed the maximum speed of the centrifuge or centrifuge.
(3) Be sure to leave the centrifuge after reaching the preset speed; if there is any abnormality, stop immediately.
(4) Normally, you can hear the sound to see if the centrifugal condition is normal, and you can also pay attention to the vibration of the centrifuge.
(5) After using a sample of high salt solution such as ammonium sulfate, be sure to wash the centrifuge and clean the centrifuge.
(6) Ultra-high speed centrifuges are extremely complex and complex, requiring additional specialized training.
3. Problems and review
(1) Why is the centrifuge above high speed frozen or vacuumed?
(2) You have carefully balanced the two sample centrifuge tubes, but after starting the centrifuge, the imbalance still occurs. After the machine is stopped, it is taken out and weighed again. It is found that the two centrifuge tubes are still balanced. Why does this happen? balance?
(3) Centrifugal gyro is generally divided into two types: swaying bucket bucket and angular angular. What is the difference in usage?
(4) In the centrifugal conditions described in the general paper, someone recorded a rotational speed of 8,000 rpm, and someone recorded a centrifugal gravity such as 10,000 g. What is the difference between the two? Which is more appropriate?
4. Use the procedure, usually register before using the centrifuge, please develop registration habits.
(1) After setting the service temperature  usually 4 °C, first place the centrifugal turret into the centrifuge chamber, pay attention to the axis of the centrifuge, and close the door, the temperature of the centrifuge chamber begins to drop, and the pre-cooling time should be sufficient.
(2) Put the sample into a suitable centrifuge tube, balance the weight with both balances, cover the centrifuge tube and tighten.
â—† Note that the centrifuge tube is only 70% full. Although it is covered, it may leak out due to too strong centrifugal force.
â—† Most of the centrifuge tubes are covered with a lid. Note that the lid of the tube should be balanced.
â—† Centrifuge tubes are usually placed on crushed ice. When removing the balance, wipe off the ice-crushing liquid.
â—† The centrifuge tube that is placed in the order should be equilibrated with another centrifuge tube filled with clean water.
(3) Place the well-balanced centrifuge tube symmetrically into the centrifuge, cover the lid of the centrifuge, and pay attention to the tightening.
â—† If the lid of the centrifuge is not tightened, it will fall out during centrifugation, causing great damage!
(4) Close the centrifuge door and adjust the required speed and time on the instrument panel, for example 8,000 rpm î–„ 30 min.
â—† Note that the speed used must not exceed the limit of the centrifuge. The maximum speed is usually written on the centrifuge. For example, the maximum speed of the TGL-20M is 20,000 rpm. However, if the centrifuge is too old, it must be lowered.
â—† The speed and time settings should not be too high. For example, if you can use 7,000 rpm, do not use 8,000 rpm.
(5) After confirming that all the steps are correct, press the Start button to start, and the centrifuge will gradually accelerate. At this time, it should be closely monitored.
â—† Some old-fashioned time buttons, when set below 5min, must be turned 10mins and then turned back to 5min.
â—† When pressing the Start button, the hold time should not be too short. Please keep pressing for about one second before releasing.
â—† It is the most dangerous when starting to accelerate. If you find that the sound is wrong or if there is a big shock, please press Stop immediately.
(6) Wait until the centrifuge reaches the desired speed and make sure everything is normal before leaving.
(7) When the centrifugation is completed, the hatch can be opened after the centrifuge is completely still; please take out the centrifuge tube as soon as possible, first observe whether the centrifuge tube is completely, and the position of the sediment, pour out the supernatant as soon as possible, be careful not to precipitate Get turbid.
â—† Regardless of the supernatant or precipitation, please use a clean beaker to collect the supernatant to avoid mistakes.
â—† Be careful when dumping the supernatant so as not to pour out the sediment together; if you accidentally mix it together, you must come back again.
â—† If there is a leak in the centrifuge tube, find out the cause and clean the centrifuge or centrifuge chamber immediately.
(8) In the neutral between the two centrifugations, it is not necessary to take out the centrifuge, but cover the door and do not allow hot air to flow into the centrifuge compartment.
(9) After all the use, remove the centrifuge to clean it, rinse it with tap water, and put it upside down to dry. The centrifuge door should be opened. After the ice is melted, wipe it and clean it. If any liquid leaks out, wash it with water. Also check back the balance of the balance tube and the tabletop, it is easy to get dirty, and it must be carefully cleaned before leaving.
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