isoelectric point

The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). However, pI is also used. For brevity, this article uses pI. The net charge on the molecule is affected by pH of its surrounding environment and can become more positively or negatively charged due to the gain or loss, respectively, of protons (H).

Surfaces naturally charge to form a double layer. In the common case when the surface charge-determining ions are H/HO, the net surface charge is affected by the pH of the liquid in which the solid is submerged.