How does NaCl influence anion migration?

[glasses]

How does NaCl influence anion migration?


Options:

1. Na+ ions bind to the anions and make them dissolve in water and so travel with the mobile phase

2. Cl- ions compete to bind to the PEI and displace anions so they travel with the mobile phase

3. NaCl raises the pH making anions bind less strongly to the PEI and so travel with the mobile phase

4. NaCl lowers the pH making anions bind more strongly to the PEI

5. Na+ ions bind to anions and make them dissolve in water while Cl- ions compete to bind to the PEI and displace anions so they travel with the mobile phase

[Markus Laeubli, Metrohm]

I don't get it. What do you mean with PEI?

To your options:

1. In aqueous phase sodium and chloride are fully dissociated.
3. and 4. Sodium chloride will not change the pH of the solution (unless you get any reaction with sodium or chloride).
5. Sodium in aqueous solution will not bind to anions see 1.

[glasses]

PEI
Polyethyleneimine cellulose plates used in ion exchange chromatography.
I think the answer is option 2 but I'm not sure.