AEX of XOMA 3AB Antibodies at pH 6.0. Both Ab-A and Ab-B antibodies bound to the anion-exchanger at pH 6.0, however, the Ab-A oxidized variants were not as well resolved as at pH 7.5 (Figure 2) and Ab-B, again, eluted as a single major peak indicating a lack of selectivity for oxidized forms. Ab-C flowed through as was the case at pH 7.5 and hence, was not subjected to further investigation. The binding of the neutral pH antibody, Ab-A (pI=7.4), at pH 6.0 was somewhat unexpected based on theoretical pI predictions and emphasizes the importance of empirical assessment of charge behavior.