New materials for chromatographic applications
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The development of new chromatographic materials is a very active field within separation sciences providing improved efficiency for current separation methods and allowing the realization of new ones. The work presented in this dissertation focuses on the development of two new chromatographic materials: a stationary phase based on surface confined ionic liquids and hafnia support monolithic columns for chromatography. Silica particles were chemically modified with methoxysilane derivatives: 1-methyl-3-(trimethoxysilylpropyl)imidazolium bromide and 1-butyl-3-(trimethoxysilylpropyl)imidazolium bromide and used as the stationary phase for HPLC. The modified silica was characterized by thermogravimetric analysis (TGA) and NMR spectroscopy. The ionic liquid moiety was predominantly attached to the silica surface through two silanoxane bonds of the silane derivative. Columns packed with the modified silica material were tested under HPLC conditions. Evaluation of the stationary phase for HPLC was performed using aromatic carboxylic acids as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic interaction, and other electrostatic interactions. A monolithic column consists of a porous structure inside of a tube (or channel) that forms a continuous bed of chromatographic material. These type of columns present an alternative to packed columns due to their high permeability, absence of frits to confine the packing material, and ease of fabrication. The most common monoliths are based on silica support, polystyrene or polymethacrylate polymeric structures, or acrylamide gels. A new type of monolithic structures based on hafnium oxide (i.e., hafnia) was synthesized using a sol-gel process. The processing reactions and conditions were studied using different analytical methodologies (i.e., pH measurement, FTIR and NMR spectroscopy), in an effort to understand the critical parameters leading to the hafnia monolithic structure. This would allow control of the synthetic conditions to provide materials with desired physicochemical characteristics that can have an impact on chromatographic performance. To understand the sol-gel process in the solution phase, a 177 Hf NMR method was developed to conduct the study of the aqueous chemistry of Hf(IV); to the best of our knowledge, this is the first observation of the 177 Hf NMR signal. Characterization of the hafnia monolithic structure was also performed using TGA, fluorescence spectroscopy and XRD.