Density gradient system. I. Formation and fractionation of density gradients

The instrumentation of a precise yet flexible system for the formation and fractionation of linear density gradients is described. The use of a special peristaltic pump and gradient-forming chambers permits the rapid formation of both dilute and concentrated solutions into ca. 5 to 300 ml of gradient. This gradient can be delivered to a single centrifuge tube or equally apportioned to as many as 24 tubes.The special peristaltic pump, which is described in the paper that follows, delivers the concentrated solution into the gradient-forming chamber as well as conveying the gradient from the chamber to the special centrifuge tube. A capillary in the wall of the tube conveys the gradient to the bottom, where it is dispersed into 18 equidistant orifices. This dispersion permits the rapid formation and fractionation of the gradient without disruption. A presettable counter coupled to the peristaltic pump permits the gradients to be apportioned into equal volume fractions.Results obtained with both dilute and concentrated gradients are presented.