| The size and density of the particles separated by the selection of the centrifugation method are quite different: normal speed, high-speed centrifugation; if two or more particles of different sizes and densities are separated from the sample solution: differential centrifugation; ultracentrifugation: differential centrifugation and density Gradient centrifugation, which in turn divides the rate zone by centrifugation and iso-density centrifugation. 1. Differential centrifugation uses different centrifugal speeds and times to separate particles of different sedimentation speeds in batches; Differential centrifugation: Principle: The method of gradually increasing the centrifugal speed or alternating the low speed and high speed to separate the particles with different sedimentation speeds at different separation speeds and different centrifugation times is called differential centrifugation. When centrifugation is carried out under a certain centrifugal time with a certain centrifugal force, the sediment of the largest and heaviest particles is obtained at the bottom of the centrifuge tube, and the separated supernatant is centrifuged at the rotation speed to obtain the second part. The "precipitation" of large and heavier particles and the "supernatant" containing small and light particles, so that multiple centrifugation can separate the different particles in the liquid. At this time, the precipitate obtained is impure and needs to be resuspended and re-centrifuged (2-3 times) to obtain relatively pure particles. Often used to separate cells and viruses from tissue homogenates. 2. Density gradient centrifugation is also called a method of speed-zone centrifugation and separation of substances with close sedimentation coefficients; Principle: When there is a difference in sedimentation coefficient between different particles, under certain centrifugal force, the particles will settle at a certain speed and form a zone on different regions of the density gradient. The media gradient should be preformed and the maximum density of the media should be less than the density of all sample particles. Commonly used are sucrose and glycerin; The preparation of the density gradient liquid is performed by using a gradient mixer to form a density gradient which is gradually increased from the nozzle to the bottom of the tube; Operation: Carefully place the sample on the surface of the density gradient solution before centrifugation and centrifuge to form a zone. After centrifugation, particles of different sizes, shapes, and certain sedimentation coefficients form a plurality of discontinuous zones with clear interfaces in the density gradient liquid; It can be used to separate nucleic acids, proteins, ribosomal subunits and other components. 3. Principle of equal density centrifugation: When there are differences in buoyancy density between different particles, in the centrifugal force field, in the density gradient medium, the particles may settle down or float upwards until they are exactly equal to their respective densities. Forming zones on the top to separate the materials of different buoyancy densities; The difference: the centrifugal medium, the density gradient range is different from the density gradient centrifugation, and the density of the particles to be separated is in the range of the density of the centrifugal medium. The medium is: barium chloride, barium sulfate, barium bromide, triiodobenzene derivatives and the like. Operation: Mix the medium solution with the sample solution and centrifuge for a sufficient time. The medium gradient does not need to be prepared in advance. During centrifugation, the medium medium and sample with uniform density are mixed and filled into a centrifuge tube, and a gradient is formed by centrifugation to redistribute the particles in the gradient. Often used to isolate nucleic acids, subcellular organelles and plasmids. |
Plant extract is a kind of product that takes plant as raw material, uses appropriate solvent or method. According to the use needs of the final product, through physical and chemical extraction and separation process, directional acquisition and concentration of one or more effective components in plants, without changing the structure of its effective components. The product concept of plant extracts is relatively broad. According to the different components of the extracted plants, they form glycosides, acids, polyphenols, polysaccharides, terpenoids, flavonoids, alkaloids, etc.
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