HPLC Separation of Selected Cardiovascular Agents on Underivatized Silica Using an Aqueous Organic Mobile Phase

High performance chromatographic separations of selected cardiovascular agents (propranolol, atenolol, metoprolol, verapamil, diltiazem, nifedipine, clonidine and prazosin) on underivatized silica using aqueous phosphate buffer - acetonitrile mobile phases were studied. Mobile phases differing in organic modifier concentration, ionic strength and buffer pH were prepared and tested for chromatographic separation of selected mixtures of the analytes grouped according to pharmacological activity. The best separations of all analytes were obtained using a mobile phase of 60:40 v/v aqueous pH 3 phosphate buffer - acetonitrile at a 1.0 mL/min flow rate. Substitution of methanol for acetonitrile gave increased retention of the analytes with some reduction in column efficiency measured as plate counts. Although ion-pairing appears to be the primary interactive force between the silica column and the analytes, other forces such as hydrogen bonding and hydrophobic interactions are also involved in the separation.