First, the working principle of the centrifuge
During the high-speed rotation of the centrifuge, the movement caused by the centrifugal force causes the solid matter suspended in the liquid to form a precipitate, that is, the object with a larger mass or volume in the suspended fluid moves in the direction of the largest radius of the rotor, and the mass or The smaller volume is deposited near the radius of the rotor. Above we mentioned the concept of centrifugal force. A centrifuge is a machine that generates centrifugal force. The centrifugal force is related to the rotor radius, rotation speed and sample quality: namely F = Rmω2 (F: centrifugal force: R: radius: m: sample quality: w: rotation speed). One of the parameters is also one of the distinguishing standards for the centrifuge grade. The centrifuge will give the maximum speed and centrifugal force of the centrifuge when it leaves the factory. We all know that the radius of the rotor and the quality of the sample are constant during operation, and only the speed can be changed by control. Therefore, we often use the speed to describe a centrifuge. Such as: high-speed centrifuge, ultra-high-speed centrifuge.
2. Classification of centrifuge:
1. According to the speed, it can be divided into: low speed centrifuge, high speed centrifuge and ultra high speed centrifuge;
2. According to the temperature requirements, it can be divided into: ordinary centrifuges and refrigerated centrifuges;
3. According to the different rotors, it can be divided into: horizontal rotor centrifuge and angle rotor centrifuge;
4. According to the size of the centrifuge, it can also be divided into: floor-standing centrifuge, desktop centrifuge, handheld centrifuge, etc .;
5. According to the grade of centrifuge, it can be divided into ordinary centrifuge and precision centrifuge.
Ordinary centrifuges have few functions and are not precise in terms of speed and capacity. For example, the maximum speed of an ordinary centrifuge is 5000 rpm, but the actual speed cannot reach 5000 rpm. Such a centrifuge is only suitable for ordinary centrifugal work, such as: separation of serum and concentrated urine. The precision centrifuge has many functions, accurate speed and capacity, and is suitable for some experiments that require high centrifuges, such as PCR experiments, blood component separation (used in blood stations), etc. Choose an ordinary centrifuge, according to the size of the workload, mainly from two aspects of speed and capacity.
3. The following details the issues that should be noted when purchasing a precision centrifuge:
(1) Speed:
Centrifuges are divided into low-speed centrifuges (<10000rpm / min), high-speed centrifuges (10000rpm / min to 30000rpm / min), ultra-high-speed centrifuges (> 30000rpm / min), each centrifuge is rated The maximum speed refers to the speed under no-load conditions, but the maximum speed varies according to the type of rotor and the size of the sample mass. For example, the rated speed of a centrifuge is 16000rpm / min, indicating that the rotor rotates 16,000 times per minute when no-load. After adding the sample, the speed will definitely be less than 16000rpm / min. Different rotors have different maximum speeds (an imported centrifuge can be equipped with multiple rotors). The horizontal rotor can reach 5000rpm / min, but the angle rotor can reach about 14000rpm / min. For specific differences, please consult the product sales staff and Relevant technical personnel of the production plant, so the choice of speed should be cautious. The maximum speed of the selected centrifuge is higher than the target speed. Such as: the target speed is 16000rpm / mIn, the maximum speed of the selected centrifuge must be higher than 16000rpm / min.
(2) Temperature:
Some samples (such as proteins, cells, etc.) will be destroyed in a high temperature environment. This requires the selection of a refrigerated centrifuge, which has a rated temperature range. The heat generated by the centrifuge at high speed and the refrigeration system of the centrifuge are balanced at a certain temperature (generally the samples of freezing and centrifugation need to be maintained at 3 ℃ ~ 8 ℃), the specific amount can also be related to the rotor, such as a centrifuge The rated temperature range is -10 ℃ ～ 60 ℃, when the horizontal rotor is installed, it can reach about 3 ℃, and if it is an angle rotor, it can only reach about 7 ℃. This point should also be consulted in detail with the product sales staff and the manufacturer. Technical staff.
(3) Capacity:
How many sample tubes need to be centrifuged each time, and how much capacity each sample tube needs, these factors determine the total capacity of a centrifuge. In simple terms, the total capacity of the centrifuge = the capacity of each centrifuge tube × the number of centrifuge tubes, the total The size of capacity and workload are matched.
(4) Rotor:
The rotors of the centrifuge are mainly divided into two types: horizontal rotors: the hanging blue is horizontal when running, at right angles to the rotating shaft, the sample concentrates the sediment at the bottom of the centrifuge tube: angular rotor: the centrifugal vessel forms a fixed angle with the rotating shaft, and the sample deposits Focus on the bottom of the centrifuge tube and the side wall near the bottom. If you want to concentrate the separated sample on the bottom of the centrifuge tube, choose a horizontal rotor. If you want to concentrate the sample on the bottom of the centrifuge tube and the side wall near the bottom, choose an angle rotor. There are some special tests or special samples that require special rotors such as: large-capacity hanging baskets (mostly used in blood stations), microplate rotors, slide rotors, PCR rotors, test tube rack rotors and capillary rotors. The rotor has a fixed specification, which is combined with the capacity of the centrifuge. For example, a 36 × 5ml angle rotor determines both the type of rotor and the capacity of the centrifuge, so the choice of rotor is very important.
(5) Control system:
High-end centrifuges all use microcomputer control systems. These control systems can not only ensure the safe operation of the centrifuge but also automatically complete the work tasks. Many centrifuges now have better user-friendly control systems. For example: rotor identification function, safety lock function, fault prompt function, acceleration and deceleration curve and so on.
In addition to the above points, we must pay attention to some details and necessary accessories. The main component of the centrifuge is a motor. The motor is divided into a carbon brush motor and a carbon brushless motor. The former has been eliminated. Most of the current centrifuges are carbon brushless motors, and some motors also have a brake function. Refrigerated centrifuges also have differences in refrigeration, and the current environmentally friendly technology is of course fluorine-free refrigeration. In addition to this, the noise problem must be considered, and the centrifuge with less noise should be selected as much as possible, so as to maintain a comfortable experimental environment. Care should also be taken in terms of accessories. Some experiments require special centrifuge tubes (for centrifugal toxic samples or samples requiring ultra-high-speed centrifugation). Such centrifuge tubes must be equipped with corresponding tube sleeves to be safer. There are also some special sample containers (irregular sample bottles, blood bags, etc.). These details and accessories must be carefully considered when selecting a centrifuge, otherwise normal work will not be possible. The price of three centrifuges. The domestic centrifuges and imported centrifuges are very different. The centrifuges with the same function are imported about three times that of domestic ones. The prices of centrifuges of the same grade in China are also different from each other, mainly distinguished in product performance and material selection. It is also related to the manufacturers' R & D capabilities. In terms of performance, centrifuges with freezing are much more expensive than ordinary ones. The more control programs and functions, the higher the price of the centrifuge. The big difference is the configuration. Sometimes the price of accessories will be higher than the price of the host. When purchasing, please pay attention to the rotor (number and type) selected in addition to the host, plus the necessary centrifuge tubes, tube sleeves, special centrifuge bottles or blood bags.
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