USE OF DENSITY GRADIENTS IN A DISK CENTRIFUGE

Conditions were examined under which stable sedimentation occurs in a disk centrifuge. Temperature gradients, largely caused by evaporative cooling at the spin-fluid meniscus, appeared to be the primary cause for convective streaming and its deleterious effects in the determination of particle size distributions. The importance of density gradients in the stabilization of the spin fluid was established. The advantage of converting the spin fluid with a layer of nonvolatile oil was demonstrated. This gives rise to more stable baselines and allows multiple consecutive sample injections without change of spin fluid. The modification of the Stokes equation for a spin fluid with a concentration gradient and for consecutive sample injections is given.