Kinetic performance of reversed-phase C18 high-performance liquid chromatography columns compared by means of the Kinetic Plot Method in pharmaceutically relevant applications

Four fully porous C18 columns (Hypersil Gold, ACE3, Xbridge and Gemini NX), widely employed in the pharmaceutical industry, were compared in terms of efficiency and analysis speed with the Kinetic Plot Method. Weakly basic, medium-sized, N-containing pharmaceutical compounds from GlaxoSmithKline Research and Development were used as test molecules. Isocratic elution was carried out at pH 4.5 and pH 8.0 with acetonitrile as organic modifier. The columns under evaluation included highly pure silica supports (Hypersil Gold, ACE3) and hybrid polymer-silica supports (XBridge, Gemini NX). Both types of columns claim for nearly absent secondary interactions with ionized silanol groups and are therefore applicable in a wide pH range. This is an important feature for method development purposes in pharmaceutical industries. The Kinetic Plot Method was used to compare the support characteristics and assess the kinetic performance of the columns in different experimental conditions. Although the evaluated columns have roughly identical particle diameters (from 3.0 to 3.5 μm) according to their manufacturers, large differences in kinetic performance were observed at pH 4.5 that can be accounted for by different flow resistances, porosities and average particle diameters, experimentally determined from scanning electron microscopy and laser light scattering experiments on loose stationary phase material. The ACE3 column was the best performing support among the evaluated columns, due to its excellent efficiency and average flow resistance. The better performance of the ACE3 column was due to its better packing quality, as could be derived from its impedance plot. Kinetic plots of resolution of a critical pair versus analysis time and column length were established at pH 8.0. These plots can be used as a method development tool to tailor the separation conditions to the required resolution of a given critical pair, combining efficiency and selectivity features of the column.