Exploring new separation media for liquid phase separations
Santiago Capeles, Lisandra
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The main focus of this thesis is column technology for liquid phase separations; this is a vital area of research in liquid chromatography (LC). The development of new support materials and stationary phases is critical to obtain selective, efficient, and fast separations. Research efforts described herein involved the synthesis of separation materials; these include silica based and metal oxides monoliths. Silica based monoliths have also been modified with carbon based nanoparticles (i.e., carbon dots and nanodiamonds). These materials were characterized by means of various spectroscopic and imaging techniques (e.g. ATR, DRIFT and transmission FTIR, and SEM). Initial chromatographic evaluation was also performed using CEC, LC, CLC and metal oxide affinity chromatography. Mass spectrometry was utilized to evaluate a specific application of metal oxide materials. The chromatographic performance of sub-3 μm superficially porous materials and a 2.5 μm totally porous material was evaluated. The main goal of the study was to evaluate and compare the performance of the HPLC columns based on the following criteria: efficiency, analysis time, methylene selectivity, mass loadability, and silanol activity. The columns studied were the Phenomenex C18 Luna ® 2.5 μm column, the Advanced Materials Technology C18 Halo(TM) 2.7 μm, and the Phenomenex C18 Kinetex(TM) 2.6 μm. The Luna ® 2.5 μm particles are totally porous while the Halo and the Kinetex(TM) particles are superficially porous. High column efficiencies were obtained with the superficially porous 2.7 μm Halo and 2.6 μm Kinetex(TM) as well as with the totally porous packing materials included in this study. However, faster separations can take place with the superficially porous materials maintaining modest pressures. The selectivity of carbon-based nanoparticles (CNPs) has attracted some interest in separation science. We have explored the immobilization of CNPs on silica based monolithic columns as potential stationary phases; these include nanodiamonds (NDs) and carbon dots (C-dots). The surface properties of the C-dots may provide interesting adsorptive characteristics as chromatographic materials. A silica monolithic column was prepared and carbon dots were immobilized as stationary phases for LC. The material was characterized and it was evaluated under LC conditions. The exploration of new modifications on the allyl silica hybrid monolith by grafting a surface confined ionic liquid and the immobilization of nanodiamonds was also explored. The monolith synthesis, characterization, and surface modifications are discussed and the initial chromatographic evaluations are presented. Lastly, the enrichment of phosphorylated peptides using Group (IV) metal oxide monolithic materials was investigated. We evaluated and compared the isolation and enrichment of phosphorylated peptides using metal oxides, such as zirconia and hafnia, using the model protein β-casein. Heat treatment of the metal oxides hafnia and zirconia materials seemed to influence the selectivity towards singly and multi phosphorylated peptides. Hafnia, when treated to 1100°C, showed enrichment/isolation characteristics that are more selective than commercially available materials towards monophosphorylated peptides. On the other hand, zirconia treated at 500°C showed, to a large extent, preferential enrichment for tetraphosphorylated peptides. The materials reduced complexity and facilitated the detection of phosphopeptides in mass spectrometric analysis of tryptic digests.