Reversed-phase liquid chromatography of lisinopril conformers

The effect of flow rate, temperature, pH, organic solvent and counter ion on peak shape and separation of the cis and trans conformers of lisinopril are investigated by HPLC. It was demonstrated that complete separation of the two isomers can be achieved at low temperature at either neutral or low pH together with appropriate type and concentration of organic solvent, whereas the elution of lisinopril as a single peak is favored by a decrease of flow rate, elevated temperature, choice of organic solvent (type and amount) and the use of an appropriate counter ion concentration.