Ion-exclusion chromatography of aliphatic carboxylic acids on an unmodified silica gel column

In order to demonstrate the effectiveness of a silica gel column in ion-exclusion chromatography, the elution behavior of aliphatic carboxylic acids was investigated on an unmodified silica gel column having cation-exchange characteristics. When water was used as an eluent, the elution order of the carboxylic acids was dependent on the pKa and the hydrophobicity, but the resolution between strong acids, e.g. HNO3, and carboxylic acids was not satisfactory. Therefore, the composition of eluents containing sulfuric acid and organic modifiers was investigated for the separation of HNO3 and C1–C10 aliphatic carboxylic acids. When 0.5 mM sulfuric acid containing 0.05% heptanol was used as an eluent, an excellent ion-exclusion chromatographic separation was achieved in 30 min using UV-detection at 220 nm.