One usually tries to avoid purifying a protein at its isoelectric point because it may precipitate when in a concentrated state, although this is not always a problem.

Ni affinity chromatography is usually done at a pH between 7 and 8, with better binding at the high pH end offset by more non-specific binding.

Metal ion affinity chromatography happens irrespective of protein’s pI. Histidyl residues must not be protonated.

Thank you all for the replies.