SEC of polyelectrolytes polyanions

For low MW salts, K eC nd its ionic strength dependence are primarily determined by solute-substrate interactions, usually electrostatic, including the Donnan equilibrium between the mobile phase and the gel phase. Deviation from Kv ec = 1 can be attributed with confidence to such effects. For polyions, the ideal or unperturbed value of K jeC ( °eC difficult to identify furthermore, because of intrapolymer repulsion and concommitant chain expansion (30), itself is dependent on ionic strength. Consequently, derivations from ideal SEC due to charge interactions may go undetected, and possibly only the more dramatic cases are recognized in the literature. 

Most packings for aqueous SEC bear a negative surface charge, especially at neutral or high pH. Therefore, polyanions commonly elute early, but this effect can always be reduced by the presence of simple electrolyte. On the other hand, the adsorption - typically irreversible - of polycations on siliceous supports is not so easily dealt with. The SEC of polycations is therefore discussed in a separate section. 

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