one. Centrifuge classification:
There are three international classification methods for centrifuges: by purpose, by speed, and by structure.
Classified by use : divided into preparative centrifuges and preparative analytical centrifuges.
Preparative centrifuge: A centrifuge that only separates and concentrates and purifies the sample.
Preparation and Analysis Centrifuge: It can not only separate and concentrate the sample, but also can observe, take photos, measure, digital output and print the centrifuge of the sample through the optical system.
Classified by speed: divided into low speed centrifuge, high speed centrifuge, ultracentrifuge.
Low speed centrifuge: The speed is within 10000 rpm or the relative centrifugal force is within 15000 × g .
High-speed centrifuge: The speed is within 10000 ∽ 30000 rpm or the relative centrifugal force is within 15000 ∽ 70000 × g .
Ultracentrifuge: The rotation speed is above 30,000 rpm or the relative centrifugal force is above 70,000 × g .
Classified by structure :
Generally, high-speed and low-speed centrifuges are classified according to structure and function, and there are many varieties, and there is no uniform standard for each manufacturer. Can be divided into desktop centrifuge, multi-tube micro-tabletop centrifuge, cell smear centrifuge, blood washing desktop centrifuge, high-speed refrigerated centrifuge, large-capacity low-speed refrigerated centrifuge, low-speed refrigerated centrifuge, desktop high-speed refrigerated centrifuge, desktop Low-speed automatic balancing centrifuges, etc. In addition, there is a triple-type (five-type) high-speed refrigerated centrifuge in foreign countries, which is specially used for continuous centrifugation.
two. Rotor classification application and characteristics
The rotor is the core component of the centrifuge for separating the sample. The rotor specifications and the variety are important indicators for measuring the mastery of the centrifuge production technology. The rotor can be generally divided into the following five categories:
Fixed angle rotor ( Eixed-Angle-Rotor ):
It is mainly used to separate particle samples with significant differences in sedimentation speed. The distance the particles move in the fan-shaped solution is very short, and the particles hitting the outer wall slide along the wall of the tube to the bottom of the tube to form a precipitate, so that the rotor can collect the precipitate quickly. During the separation process, due to the action of the tube wall, strong convection will be caused in the centrifuge tube, which will have an adverse effect on particles having the same sedimentation rate.
A swing rotor (Siwing-Bucket-Rotor):
Mainly used for sample density gradient centrifugation. The moving distance of the particles is long, and the position of the components in the solution relative to the wall of the tube does not change during the centrifugation and after centrifugation, so the centrifugal effect is good, but the particles are scattered radially from the rotation in the centrifugal field. Instead of sinking in parallel with each other. The particles hit the outer wall and slide along the tube wall to the bottom of the tube, thus also causing convection. Will produce (but less than the fixed-angle rotor) at low speed to start or stop the influence of vibration separation, a swing rotor has two kinds of open and closed, general preparation capacity, speed is less than 10000 RPM, a centrifugal field within at 16000xg, Made in an open type, mainly used for the initial separation of samples. The preparation capacity is smaller than the former, the rotation speed is greater than 10000 RPM , and the centrifugal force field is above 16000×g . In order to reduce the influence of wind force, it is generally closed, mainly used for separation and density gradient centrifugation of mitochondria, chloroplast, and nucleus.
Continuous centrifugal rotor (Continuous-Flow-Rotor):
It is mainly used to separate small particles in the suspension medium at high speed. For example, the cells are separated in the medium. During the operation, the suspended sample flows into the centrifuge tank from the center of the rotor at a certain speed. Due to the different weight of the components in the solution, Under the action of centrifugal force field, heavy particles have large inertial centrifugal force and fast sedimentation. When the flow rate increases (decreases) to a certain value, heavy particles will remain at the bottom of the outer edge of the centrifugal cell, and the medium will flow out from the outlet and take away. For light particles, the components are collected by flushing the components out of the centrifuge or leaving them in the rotor. This rotor separates whole cells or large subcellular particles by centrifugal elutriation, in sterile and cryogenic conditions. The separated components are capable of maintaining activity and high recovery. If the flow direction is opposite to the direction of the centrifugal force, the particle running speed is reduced, which is equivalent to an increase in the running distance, thereby improving the resolving power.
Zone rotor ( ZOnal-Rotor ):
It is mainly used for high-density density gradient centrifugation. When the amount of samples required for the experiment is large, and the flattened rotor is limited by the amount, it is better to use zone centrifugation. It consists mainly of a rotor body with four blades and a sealing system. The rotor body and four blades divide the centrifugal pool into four fan-shaped chambers, preventing the solution from rotating in the centrifugal pool. The blades have radial conduits and the solution passes through the conduit. The center flows to the outer wall of the rotor. Care should be taken when loading and sampling. The loading is usually carried out at 2500 ∽ 3000 rpm . First, the lighter part of the gradient liquid is pumped into the rotor through the sealed pipe. Due to the inertia force, the gradient liquid A uniform layer is formed in the vertical direction of the outer wall of the rotor, and the higher density gradient liquid is pumped in turn. As the density increases and the gradient liquid is continuously pumped, the lower density gradient liquid is pushed toward the center until the rotor Completely filled, then the sample to be separated (the density of which is lower than the light density of the zui in the gradient) is added through the central infusion tube of the sealing assembly, and then a lower density solution is injected to replace the sample near the center. Bahrain, the seal assembly is removed, covered with the rotor cover, centrifuged after a certain predetermined time, the rotation speed reduced to 2500 ∽ 3000rpm, and a seal assembly mounted on the infusion tube By pumping the liquid into a denser liquid rotor successively extruded from light to heavy.
A zonal rotor with avoiding wall effects (Walleffects) centrifuge tube caused by interference and to improve the resolution.
Vertical rotor ( Vertical-Tube-Rotor ):
It is mainly used for density gradient centrifugation of samples in a short time. The flattened rotor has a long displacement distance and high resolution. The separated components have a wide band and are easy to recover, but the time required for the vertical rotor separation is equal to the diameter of the centrifuge tube. Before the rotor rotates, the density of the density gradient solution in the tube changes along the direction of gravity. After the rotation, the density of the solution gradually changes to the direction of the centrifugal force (horizontal direction). After the end of the centrifugation, the density change direction of the solution changes along the vertical direction due to gravity. The change forms a density gradient in the vertical direction. Since the centrifuge tube is placed vertically, the distance of the solution particles is shifted by the diameter of the centrifuge tube. The centrifugation time is short, and the zone of the sample component is wide after centrifugation. However, because the centrifugation time is short, the particles are not sufficiently separated, some components will be lost, and the contact surface of the zone and the gradient medium is large, and it is easy to spread. After the shutdown, the density is redirected and easy to mix, so the effect of centrifugation is achieved, and the vertical rotor is not flattened.
The speed of the centrifuge rotor is related to the material and strength of the rotor. Generally, a super-hard aluminum alloy ( LC4 ) with good strength and light weight is used , and the ultra-centrifuge uses titanium alloy ( TiC4 ). Generally speaking, the rotor of the same centrifuge is light in weight and small in capacity, and the rotation speed is low. Maintenance and life management of the rotor are described in later chapters.
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