Separation of pharmaceutical bases from neutral and acidic components by capillary electrochromatography

Abstract

Capillary electrochromatography (CEC) has proved to be applicable to the separation of neutral and acidic (chromatographed in their ion-suppressed mode) compounds but a major factor holding back its further development has been its perceived inability to analyse basic compounds. In this paper we demonstrate that the addition of a competing base, such as triethylamine (TEA) or triethanolamine (TEOA), to a low pH buffer can achieve excellent CEC analysis of a range of strong pharmaceutical bases. Acceptable peak symmetry and efficiencies of up to 510000 plates m^–1 were obtained for bases such as procainamide, nortriptyline and diphenhydramine on CEC Hypersil C₁₈, C₈ and phenyl reversed-phase packing materials. The effect of TEA or TEOA concentration and mobile phase pH on the separation behaviour of the bases is discussed. In addition, the paper reports the first example of the simultaneous CEC analysis of acids, bases and neutral compounds by using a mobile phase containing TEOA phosphate at pH 2.5.