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How does the sedimentation-equilibrium method determine molecular weight?
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centrifuge
Figure 1: Tubular centrifuge
The sedimentation-equilibrium method is a technique used in an ultracentrifuge to determine the molecular weight of substances in solution.1
In this method, the material is centrifuged until it reaches a state of equilibrium within the centrifuge cell. At this point, the rate at which the material settles due to the centrifugal field is exactly balanced by the rate of back diffusion. Once this balance is achieved, the concentration of the substance is measured at various radial distances from the axis of rotation. By analyzing these concentration gradients, the molecular weight of the substance can be calculated.1