Heterogeneity of the gradients performed by the freeze-thaw method.

Gradients produced by the freeze-thaw method were analyzed at various rates of freezing. The shape of the gradient depended on the rate of freezing. At high rates the pattern did not change but at low rates the steepness of the gradient increased with time. Solutes concentrated at the bottom in a fashion which depended on the density of the solvent and on the rate of freezing. It should also be noted that the gradient was not uniform over the entire surface as the concentration of solute increased near the wall of the test tube.