COMPARISON OF HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHODS FOR THE ANALYSIS OF BASIC DRUGS

Problems that are often encountered in the high-performance liquid chromatographic analysis of basic compounds are severe peak asymmetry and low separation efficiency. In attempting to solve these problems, one can become confused by the variety of suggestions given by the specialists and by the numerous stationary phases available. In this work, the analysis of basic drugs was studied from two directions. In both approaches a set of 32 basic drugs was used, differing in basicity, polarity and number and type of nitrogen atoms. In the first approach the effect of mobile phase additives and buffers on the performance of a single column was determined. It was found that tertiary and quaternary amines can be applied successfully as silanol blockers. The latter proved to be aggressive towards silica-based stationary phases. Addition of triethylamine showed a remarkable improvement in peak shape in different columns. Other aspects, such as pK(a), retention and amount injected, were systematically studied. In the second approach, eight different columns, specially recommended for the chromatography of basic drugs, were evaluated. The chromatographic results showed great variability. As far as peak shape as a function of pH is concerned, an electrostatically shielded stationary phase was most promising for the analysis of basic compounds. This column can even be used without buffers, which can be an advantage in liquid chromatography-mass spectrometry coupling. Because some results were inconsistent with published results, a third approach was to study three columns in more detail.