Process and apparatus for forming a continuous solution gradient

The invention concerns a process and apparatus for forming a continuous concentration gradient in a solution, e.g. of sucrose, in a tube for use in the separation of macromolecules. The process comprises:- (a) introducing into a tube solutions of differing concentrations in a manner to layer said solutions therein; (b) inclining said tube to an angle with respect to the vertical; (c) rotating said tube while maintaining the contents thereof visually determinable thereby to form said continuous solution gradient; and (d) discontinuing step (c) after formation of said continuous solution gradient. Preferably the tube is secured in position magnetically.