Solid-Phase Extraction of Ibuprofen from Pharmaceuticals via Ligand Exchange Using Zirconium Dioxide

Background & Objective: The presence of Lewis acid sites on the metal oxides is responsible for a problematic elution of Lewis bases from these stationary phases due to the ligand exchange. The interactions are quite strong and the kinetics is relatively slow which is chromatographically undesirable. On the other hand, the interactions based on ligand-exchange could be employed in the solid-phase extraction. We newly tested these presumptions in the extraction process of ibuprofen (Lewis base) from hydrophobic suppositories as well as a hydrophilic oral suspension. Method & Results: The pharmaceutical formulation was dissolved in hexane (suppositories) or 50 % methanol (oral suspension) and 0.5 mL of the appropriate solution was loaded on a cartridge containing bare zirconia. After washing with methanol and water, ibuprofen was eluted by 1% ammonia in methanol. It was shown that only zirconia (in contrast to titania) was capable to extract ibuprofen from pharmaceuticals thanks to the stronger ligand exchange properties. A novel method for ibuprofen extraction using zirconia was proposed. The recoveries of ibuprofen were 95 % and 94 % from suppositories and an oral suspension, respectively. Conclusion: This paper describes the first successful utilization of ligand exchange process on zirconia in the extraction of ibuprofen from two different pharmaceuticals. It was shown the pivotal role of interactions between the carboxylic moiety and the Lewis acid sites on the zirconia surface. The procedure can be applied in case that the vehicle is not compatible with the chromatographic conditions used for the subsequent analysis of the active compound.