In crystallization by dialysis, the macromolecular concentration remains constant, as in batch methods (Fig. 1.17 b) because the molecules are forced to stay in a fixed volume. The solution composition is changed by diffusion of low-molecular-weight components through a semipermeable membrane. The advantage of dialysis is that the precipitating solution can be easily changed. Dialysis is also uniquely suited to crystallizations at low ionic strength and in the presence of volatile reagents such as alcohols.
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