| SBA-15 mesoporous silica is characterized by hexagonally ordered non-intersecting parallel pores. In stark contrast, silica gel, commonly utilized in high performance liquid chromatography as a stationary phase, consists of many interconnected channels created by the spaces between primary particles. There has been much research regarding the importance of the geometry and characteristics of porous silica in chromatography, however, since the advent of ordered materials in the early 1990's, most of the investigations into use of ordered material have failed to extensively study the effects of the highly ordered porous structure on retention mechanisms. In this study, we attempt to evaluate the effect of the characteristic parallel non-intersecting pores of SBA-15 on the thermodynamics and kinetics aspects of retention.;To achieve our goal, it was necessary to transform the native rope-like morphology of SBA-15 into the more commonly used and efficient sphere. The effects of temperature and synthesis time were evaluated. Following modification, characterization by low temperature nitrogen adsorption, thermogravimetric analysis and optical microscopy were utilized to evaluate pore structure, bonded layer characteristics and morphology.;Suitable spherical SBA-15 packed into stainless steel columns were fully characterized for void volume and interparticle volume. Based on the results produced by kinetic studies, the evidence of column obstruction showed a reduced value for the diffusion of benzene as compared to commercial silicas, while surface specific retention studies resulted in the evaluation of reduced accessible surfaces. The obstruction of the pore volume, thus limiting the surface area, is most likely attributed to a combined effect of long narrow pores, which in the spherical particles, tend to bend or twist, and to which an uneven modified layer creates instances of pore blockage of the mobile phase. |
