Relationship Study Between Reversed-Phase HPLC Retention Data and the PKa Values in a Series of 2-Amino-2-Oxazolines

In reversed-phase liquid chromatography, the retention behaviour of ionogenic compounds is strongly related to the pH mobile phase. An application is presented for three basic 5-substituted 2-amino-2-oxazolines. The pH dependence of their capacity factor values, expressed as log k'w, was investigated in a RP-HPLC procedure using a column packed with poly methacrylate. The plot of capacity factor vs pH was described by a sigmoidal curve, leading us to approach the ionization constants of the molecules. Finally, the pKa values have been discussed in regard to chromatographic parameters and to experimental conditions.