Determination of Partition Coefficient and Acid Dissociation Constant by High-Performance Liquid Chromatography on Porous Polymer Gel as a Stationary Phase

Abstract

The availability of porous polymer gel as a stationary phase in high-performance liquid chromatography (HPLC) for determination of the partition coefficient between octanol and water (Poct), and the acid dissociation constant (pKA) was examined for a wide variety of compounds.The log of capacity factor k' increased linearly with increase in log Poct, when the hydrogen bonding ability of compounds was taken into account. However, aromatic compounds that possess an amino group such as procaine, anilines and sulfonamides showed anomalous chromatographic behavior from the viewpoint of the hydrogen-bonding ability. Furthermore, quinolines and pyridines also were anomalous. With these chromatographic characteristics in mind, log Poct can be determined very accurately for various compounds by HPLC over a wide range of pH.Since this stationary phase is stable over a wide range of pH, HPLC could be run in the alkaline region, in contrast to the octadecyl silica (ODS) column, which is unstable above pH 7. From the capacity factor k' at various pH, pKA values of various acids, bases and amphoteric compounds were determined very accurately.In conclusion, the porous polymer gel can be used as a stationary phase in HPLC in a range between acidic and alkaline regions. This stationary phase is effective for determining Poct and pKA values simultaneously or separately.