density gradientmedical dictionary

<chemistry> A column of liquid in which the density varies continually with position, usually as a consequence of variation of concentration of a solute.

Such gradients may be established by progressive mixing of solutions of different density as for example: sucrose gradients) or by centrifuge induced redistribution of solute (as for caesium chloride gradients).

Density gradients are widely used for centrifugal and gravity induced separations of cells, organelles and macromolecules. The separations may exploit density differences between particles or primarily differences in size, in which latter case the function of the gradient is chiefly to stabilise the liquid column against mixing.

(12 Jan 1998)