Novel Stationary Phase Materials in Separation Science Research

Research activities in separation science continue to focus on investigations of the fundamental physical and chemical processes that influence analyte retention in liquid chromatography (LC), as well as gas chromatography (GC), supercritical fluid chromatography (SFC), capillary electrophoresis (CE), and capillary electrochromatography (CEC). Results from these fundamental studies are used to design novel stationary phase materials tailored to solve specific separation and analysis problems, and to assist in current method development and optimization. 

The Organic Chemical Metrology Group maintains on ongoing effort to study liquid and gas chromatographic stationary phases. Analytical chemists are faced with measuring constituents within increasingly complex samples, thereby necessitating the design of novel stationary phases to help meet those challenges. Chromatographic, spectroscopic, and simulation-based studies of the more traditional alkyl-modified surfaces routinely used in LC separations has been conducted over the past two decades. This has resulting in a wealth of knowledge that elucidates the predominate factors that control molecular order and disorder within these materials, which, in many instances, directly relates to their separation capability. Building upon this foundation, we are rationally designing a new generation of sorbent materials that contain "tunable" functionalities (e.g., specific-sized cavities, molecularly rigid ligands, ionic moieties to promote mixed-mode capabilities) that can be applied towards a range of emerging analytes with ever-increasing functionality. The resultant materials from these research investigations are thus intended for direct use in the measurement of structurally similar emerging contaminants, nanoparticles and biomolecules that are present in complex matrices, such as chemotherapeutics, biological samples and environmental media.

Recently we have explored novel approaches for the synthesis of a range of LC stationary phases. Based on our previous efforts to design shape-selective stationary phases for improved separations of isomers (e.g., polymeric C₁₈ and C₃₀ sorbents), stationary phases have been developed based on polymer immobilization. The resulting columns were evaluated for the LC separation of carotenoid isomers, important in the analysis of food and dietary supplement samples. Related "mixed mode" stationary phases have been prepared by incorporation of chiral selectors into the immobilized polymer phases. The resulting columns exhibited both enhanced shape selectivity, and enantioselectivity toward chiral species and thus will have importance in a range of clinical applications. Hydrocarbon phases with deliberately introduced cavities and that vary in chain length have been synthesized with the intention of separating larger molecules such as functionalized nanoparticles. Efforts have also been directed towards the synthesis of a range of extended length perfluorinated stationary phases. Perfluorinated alkane materials with sufficient chain length (C₁₅ and C₁₇) have exhibited enhanced shape recognition properties under more aqueous conditions and at significantly elevated temperatures, based on increased order of the fluorinated ligands.  

Major Accomplishments:  

• Publication of results in high-impact peer-reviewed publications (Analytical Chemistry, Analytical and Bioanalytical Chemistry)
• Patent for a novel fluorinated carboxylic acid stationary phase is presently under the US Patent and Trademarks Office review