The influence of a carbon layer deposited on a zirconia surface on the retention of polar analytes in an organic rich mobile phase.

Hydrophilic interaction liquid chromatography (HILIC) represents a modern MS-friendly approach to the analysis of polar compounds. To date especially silica-based HILIC stationary phases are utilized. Recently the papers concerning retention of polar analytes on unmodified titania and zirconia as well as a polybutadiene modified zirconia stationary phase under HILIC conditions have been published. In this work the investigation of a highly hydrophobic carbon-coated zirconia column under HILIC conditions was reported. The influence of buffer concentration, buffer type, pH and temperature on the elution and chromatographic efficiency were studied. The processes participating on the retention of polar compounds showed a multimodal character. The retention was governed rather by surface adsorption than phase partition in high ACN mobile phases. The ligand exchange remained an important retention force although the access of the analytes to the active surface was significantly hindered by the carbon coating. Besides ligand exchange and hydrophilic interactions also the hydrophobic carbon layer was involved in the retention of carboxylic acids and especially xanthines in the organic rich mobile phase.