The analysis of basic drugs by HPLC

Two methods for the high performance liquid chromatographic analysis of basic drugs have been studied. In each case the methods have concentrated on separating drugs of forensic interest, based on specially designed test solutions of analytes selected to represent most of the commonly encountered classes of drug compounds. In the first case, a HPLC method was developed on unmodified silica using an aqueous methanolic eluent of high pH. The buffer was prepared from two organic sulphonic acid amines, 3-(cyclohexylamino)-1- propanesulphonic acid (CAPS) and sodium 3-(cyclohexylamino)-2-hydroxy-1- propanesulphonate (CAPSO-Na). The method was shown to be highly reproducible within a single laboratory. The long term stability of the unmodified silica stationary phase was examined, using the newly developed method for the analysis of drugs as a monitor of column performance. Three columns from a single batch of silica were studied, and all showed pronounced changes in retention properties over the period of the study. Similar changes in retention properties were observed for silica stored dry and unused. These results led to the idea that an 'aging process' was changing the nature of the silica surface, probably by a process of hydrolysis of surface siloxanes. This aging process was also believed to be responsible for the appearance of distorted peak shapes for methylamphetamine, although no clearly defined mechanisms could be found to support this idea. In a second study, the application of gradient HPLC methods for the screening ·of a wide range of analytes was examined. In this case, an Inertsil ODS-2 column was used in conjunction with an acid buffered acetonitrile I water gradient. The usefulness of the 1-nitroalkanes as a retention index series was demonstrated and a good level of retention reproducibility was achieved for most analytes studied.