Analysis of Basic Drugs: A Comparison of Two Different Strong Cation Exchange-Modified LC Packings

Evidence in the literature of systematic investigation of retention mechanisms on strong cation-exchange (SCX) modified silica LC packings is lacking. In this study, the retention behaviour of selected basic drugs using a propylbenzenesulfonic acid-modified packing (Nucleosil 100SA) were compared, under similar conditions, with previous findings from a propylsulfonic acid-modified packing (Waters Spherisorb S5SCX). Eluent ionic strength, apparent pH, and solvent composition were investigated. Good efficiency (70,000 plates m^?1) and peak symmetry (<1.5) were observed using the Nucleosil 100SA packing. The use of different alkyl ‘spacer’ moieties in each packing influenced retention, with hydrophobic partitioning of analytes more evident for the Nucleosil packing compared with Spherisorb, particularly when water-containing eluents were used. On Nucleosil 100SA, non ion-exchange interactions accounted for up to 61% of retention. Despite some correlation with analyte LogP on Nucleosil 100SA, and the environment surrounding basic nitrogen moieties, retention on both SCX packings was unrelated to analyte pK _a.