Ionic strength dependence of the stability of polyelectrolyte complexes. Its importance for the isolation of multiply charged polymers

Complexes of polyanions and polycations that precipitate at low ionic strength, [I], from aqueous solutions become soluble when [I] is increased. The critical ionic strength for resolubilization [I]crit has been determined for various combinations of polyanions and polycations. [I]crit depends on the chemical nature of the polyelectrolytes. Provided the difference in [I]crit is sufficiently large, different polyelectrolytes of the same charge state can be separated via selective precipitation with the aid of an appropriate polyelectrolyte of opposite charge state. The method has been exemplified by separating albumin from polyphosphate via precipitation as polyelectrolyte complex with poly(N‐ethyl‐4‐vinylpyridinium bromide). The process was performed at pH 8, where albumin acts as polyanion.