[Zalzul]

So my textbook asks this question:

"Consider a negatively charged protein adsorbed on an anion-exchange gel at pH 8:

How would a gradient of ionic strength (at constant pH) be useful for eluting the protein?"

Should I think about this in terms of the protein remaining adsorbed on the gel?  Or, rather, the anions being able to swap places with the protein?

Is it plausible to think that if one were to gradually increase the eluent's ionic strength, more of the protein would break from the gel and pass through the column?  Or would I instead want to gradually decrease the ionic strength in order to help the anions exchange places with the protein?

My thought supporting gradually increasing ionic strength: I know that increasing ionic strength lessens the tendency for opposite charges to come together.  So I thought that by doing that, the protein might lose its affinity for the anion-exchange gel. 

My thought supporting gradually decreasing ionic strength: I also know that ionic strength matters more for smaller ions, and proteins are relatively huge.  Since ionic strength matters little for the protein, it's best to think about this in terms of helping the anions in the eluent exchange places with the protein by lessening the shielding of their charges.

I'm just seeking clarification because my textbook does not elaborate much on this.

Additional question that has more to do with the wording of the question: If one varies the ion strength, how can pH remain constant in the first place? Since pH is really a measure of the activity of hydrogen, how can you prevent ionic strength from affecting that?

Thanks in advance for anyone's help.