Characterization of Silica-Based Monoliths with Bimodal Pore Size Distribution

Abstract

Band dispersion was studied and the retention thermodynamics addressed for insulin and angiotensin II on C18 silica monoliths with a bimodal pore size distribution, covering linear mobile-phase velocities up to 1 cm/s and different temperatures. These data suggest that the influence of average column pressure on retention (between 0 and 10 MPa) is not negligible. Plate height curves were interpreted with the van Deemter equation by assuming an independent contribution from mechanical and non-mechanical dispersion mechanisms. This analysis revealed diffusion-limited mass transfer in the mesoporous silica skeleton which, in turn, allowed us to calculate an equivalent dispersion particle diameter (d(disp) = 3 microm) using the C-term parameter of the van Deemter equation. The resulting superposition of reduced plate height curves for monolithic and particulate beds confirmed that this view presents an adequate analogy. The macroporous interskeleton network responsible for the hydraulic permeability of a monolith was translated to the interparticle pore space of particulate beds, and an equivalent permeability particle diameter (d(perm) = 15 microm) was obtained by scaling based on the Kozeny-Carman equation.

Liquid intrusion and alternative methods for the characterization of macroporous materials (IUPAC Technical Report)

“…As an example, using the standard Kozeny-Carman analysis with K = 5, an equivalent spherical particle size of 15 μm is found for a chromatographic silica monolith with 1.9 μm pore size [32].…”

Preparation of methacrylate monoliths

“…From the middle of the 1990s, interest in monoliths increased dramatically. Today these materials are produced from synthetic polymers such as polymethacrylate, polyacrylamide, and polystyrene [11 -13] and natural polymers including agarose and cellulose [14], as well as from inorganic materials such as silica [15]. Commercially manufactured media are currently offered by Sepragen (USA), Merck (Germany), BIA Separations (Slovenia), Dionex (USA), and LC Packings (The Netherlands).…”

Less common applications of monoliths

“…The mesopores provide the silica monoliths with a much larger surface area of about 300 m 2 /g. Thus in contrast to common porous polymer monoliths used in liquid chromatographic mode exhibiting only about 10 m 2 /g, the silica-based monoliths afford much higher number of interactive sites and has proven to be excellent stationary phases for the separation of small molecules [16,[66][67][68][69][70]. While liquid chromatographic separations were studied in great detail, very little was known until recently about their performance in gas chromatography.…”