The isoelectric point (pI) of a molecule, such as an amino acid or protein, is the pH at which the molecule carries no net electrical charge . At this pH, the molecule exhibits no net movement in an electric field, a principle that underlies isoelectric focusing electrophoresis . For a simple amino acid like glycine, which contains two ionizable groups (-COOH with pK a 1 , and -NH3 + with pK a 2 , Figure ), the predominant species at the pI is the amphoteric zwitterion (HA). This zwitterion is in equilibrium with small amounts of its conjugate acid (H2A + ) and conjugate base (A⁻). At the pI, the H2A + and A -concentrations are equal, resulting in a zero net charge across all glycine species . Most pI estimates based on pKₐ values are derived by averaging the corresponding pKₐ values (e.g., for glycine, pI = (pK a 1 + pK a 2 )/2), assuming the zwitterion is positioned between the two ionization equilibria . However, previous derivations often overlook essential details regarding the underlying assumptions . The method presented here offers a more precise derivation of pI values using acid-base equilibria with additional considerations. This approach can be extended to more complex amino acids containing acidic or basic side chains and to determine the pH of solutions containing amphoteric species.