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Historically a cesium chloride (CsCl) solution was often used, but more commonly used density gradients are sucrose or Percoll.This application requires a solution with high density and yet relatively low viscosity, and CsCl suits it because of its high solubility in water, high density owing to the large mass of Cs, as well as low viscosity and high stability of CsCl solutions.
Differential centrifugation, on the other hand, does not utilize a density gradient, and the centrifugation is taken in increasing speeds. The different centrifugation speeds often create separation into not more than two fractions, so the supernatant can be separated further in additional centrifugation steps.
During a relatively short or slow centrifugation, the particles are separated by size, with larger particles sedimenting farther than smaller ones. Over a long or fast centrifugation, particles travel to locations in the gradient where the density of the medium is the same as that of the particle density; (ρp – ρm) → 0.
Sedimentation equilibrium in a suspension of different particles, such as molecules, exists when the rate of transport of each material in any one direction due to sedimentation equals the rate of transport in the opposite direction due to diffusion. Sedimentation is due to an external force, such as gravity or centrifugal force in a centrifuge.
Sedimentation equilibrium experiments reports the molar mass of analytes and their chemical equilibrium constants. [3] The rotor speed is adjusted such that a steady-state concentration profile c(r) of the sample in the cell is formed, where sedimentation and diffusion cancel out each other.
Isopycnic centrifugation refers to a method wherein a density gradient is either pre-formed or forms during high speed centrifugation. After this gradient is formed particles move within the gradient to the position having a density matching their own (this is in fact an incorrect description of the exact physical process but does describe the ...
Density gradient is a spatial variation in density over a region. The term is used in the natural sciences to describe varying density of matter , but can apply to any quantity whose density can be measured .
Diagram of a gas centrifuge with countercurrent flow, used for separating isotopes of uranium. A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centrifugal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radius of a rotating container.