Separation of ionized solutes
Liquid chromatography - Separation theory and methods

The mechanisms for separating these solutes are essentially based on electrostatic interactions between charged species simulataneously present in each of the two phases. It should be remembered that many organic compounds are capable of yielding ions in solution if pH is properly controlled.

Depending on pH, amino acids can be present in solution in molecular form, or as anions or cations.

Consider, for example, the case of glycine HOOC–CH ₂–NH₂ whose pk_A are 2.3 and 9.8 respectively (the former corresponds to the acidity constant of the pair –COOH/–COO ^–, the latter to the constant of the pair –NH₃ ⁺/–NH₂). Figure