Effect of buffer solution pH on the elution and separation of beta-blockers by micellar electrokinetic capillary chromatography.

Study was made of the effect of the pH of phosphate buffer (0.08 M) containing 15 mM cetyltrimethylammonium bromide as surfactant on the elution order of eleven widely used beta-adrenergic blocking agents. In the pH range 6.0-7.8 the elution order of six of the beta-blockers remained the same, while the order of five of them changed. Sotalol eluted as the sixth compound at pH 6.8 and migrated more quickly with increasing pH. Below pH 7.0 labetalol eluted before propranolol and above pH 7.0 afterwards. Likewise, the order of elution of atenolol and timolol was reversed at pH 7.0. The pH also affected the resolution; the best resolution values were achieved between pH 6.6 and 7.0 and between pH 7.4 and 7.8. The relationship between the structure of the beta-blockers described by molecular and molecular connectivity indices and the elution order and separation of the beta-blockers in micellar electrokinetic capillary chromatography at varying pH of the buffer solution is discussed.