Characterization of mesoporous silica and its pseudomorphically transformed derivative by gas and liquid adsorption
Abstract Pseudomorphism is a term introduced by mineralogist to describe phase transformation that does not change the shape of a material. Pseudomorphic process, assisted by surfactants, for mesoporous pre-shaped silica particles allows to narrow the mesopore size distribution, to increase the surface area and the pore volume without changing the initial shape of silica particles. The textural, chemical and mechanical comparisons between commercial silica LiChrospher 60 (Merck) and its pseudomorphic transformation at constant particle size and morphology opens a unique opportunity to understand the effects of such mesoporosity transformation and judge the performance of both types of mater…
Interactions of lysozyme with hydrophilic and hydrophobic polymethacrylate stationary phases in reversed phase chromatography (RPC)
Two silicas, one with a mean pore diameter of 30 nm and the other non-porous, were coated with polymethacrylates of increasing hydrophobicity in the sequence: poly-2-hydroxyethylmethacrylate (P2HEMA)1 polyethylmethacrylate (PEMA) and poly-n-octylmethacrylate (POMA). Association constants, Kass, between lysozyme and the coated silicas were determined by means of frontal analysis, and the apparent heats of adsorption, delta Happ, by means of microcalorimetry. Using Kass and delta Happ the changes in the apparent free energy, delta Gapp, and in the apparent entropy, delta Sapp, were calculated at a concentration of lysozyme < 10 mumol/l. The association between the lysozyme and the coated sili…
Sulphonic acid strong cation-exchange restricted access columns in sample cleanup for profiling of endogeneous peptides in multidimensional liquid chromatography
Abstract In this work, the pore structural parameters and size exclusion properties of LiChrospher strong cation-exchange and reverse phase restricted access materials (RAM) are analysed. The molecular weight size exclusion limit for polystyrenes was found to be about 17.7 kDa, while for standard proteins, the molecular weight size exclusion limit was higher, at approximately 25 kDa. The average pore diameter on a volume basis calculated from the pore network model changes from 8.5 nm (native LiChrospher) to 8.6 nm (diol derivative) to 8.2 nm (sulphonic acid derivative) to 6.9 nm ( n -octadecyl derivative). Additional characterisations were performed on restricted access materials with nitr…
Liquid intrusion and alternative methods for the characterization of macroporous materials (IUPAC Technical Report)
This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 μm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion–extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed…