What pH range will zwitterions tolerate?

A zwitterion will only exist as such at a pH equal to or near its isoelectric point. Isoelectric point (pI) is also sometimes referred to as isoionic point. At this point, the amino acid is neutral and does not migrate in an electric field. This allows the zwitterion to be dominant. Every zwitterion has a different isoelectric point and will tolerate a different pH range.

The boundaries within which a zwitterion will exist as such are the pKa values of the amino acid. This can vary widely depending on the chemical structure of the amino acid side chains.