[wils0645]

If I concentrate a bicarbonate buffer system by removing free water from a solution (using hydrophobic hollow fiber membranes), does that change the pH?
I use the Henderson-Hasselbalch equation:
pH = pK + log ([NaHCO3]/[CO2]).  If only free water removed, the two concentrations (NaHCO3 and CO2) increase equally resulting in no change in pH.  That is my guess.  What do you think?  The buffer system I am using is 25mM NaHCO3, 135mM NaCl.

[Borek]

Ionic strength changes, activities change, pH changes.

[wils0645]

How much of an effect would it be?

[Borek]

http://www.chembuddy.com/?left=pH-calculation&right=ionic-strength-activity-coefficients