Effect of organic solvent modifier and nature of solute on the performance of bonded silica reversed-phase columns for the analysis of strongly basic compounds by high-performance liquid chromatography

The performance of eight silica-based RP-HPLC columns was examined with nine relatively high-pit, bases of different structure using isoeluotropic mixtures of either methanol, acetonitrile or tetrahydrofuran (THF) in combination with phosphate buffer pH 7.0. Meaningful evaluation of the columns in unbuffered methanol-water and acetonitrile-water mixtures could only be obtained for low-pK(a) bases, probably due to variable ionisation effects. Buffered acetonitrile generally produced worst peak shapes for the nine higher-pK(a) bases; further improvement may be gained in some cases using THF rather than methanol. Although in general high-pK(a) solutes with reduced steric hindrance gave the most asymmetric peaks, the nature of the solute chosen to probe activity could give considerably different results of relative column performance when using a given mobile phase.