What is the pI of the beads, in otherwords at which pH are the beads neutrally charged neutrally charged?
An aliphatic COOH would be expected to have a pK of about 4 but groups on particle surfaces will have a broad range of pK due to degree of hydration. That is why potentiometric titration of CML gives a broad transition rather than a sharp inflection as in the titration of acetic acid with strong base. We have never done potentiometric titration of our magnetic but I bet it will be a broad distribution.
