The use of organic modifiers in ion exchange chromatography on alumina. The separation of basic drugs

It is shown that the selectivity of ion-exchange chromatography on alumina can be substantially improved by adding organic solvents to the aqueous mobile phase. With increasing modifier content the retention of organic cations generally passes through a maximum. This is attributed to the competing effects of enhanced solvation of the buffer cation and reduced solute ionization. The mutual interaction of pH, buffer composition, solute pK and eluent composition produces a very flexible system that can be optimized for the separation of a particular sample. As an example of practical significance, the separation of six basic drugs at pH 6 in a mixture of acetonitrile and water is presented.