Inorganic-silica monoliths

The preferentially employed approach for the fabrication of inorganic (silica) monolithic materials is acid-catalyzed sol-gel process, which comprises hydrolysis of alkoxysilanes as well as silanol condensation under release of alcohol or water [84-86], whereas the most commonly used alkoxy-silane precursors are TMOS and tetraethoxysilane (TEOS). Beside these classical silanes, mixtures of polyethoxysiloxane, methyltriethoxysilane, aminopropyltriehtoxysilane, A-octyltriethoxysilane with TMOS and TEOS have been employed for monolith fabrication in various ratios [87]. Comparable to free radical polymerization of vinyl compounds (see Section 1.2.1.5), polycondensation reactions of silanes are exothermic, and the growing polymer species becomes insoluble and precipitates... 

Although inorganic, monolithic columns attracted considerable attention in the last 10 years, the preparation of silica-based monoliths does not yet offer the broad chemical variety of precursors and porogens for specific adjustment of separation compared with their organic counterpart. The preparation of silica monoliths uses the classical sol-gel process of hydrolysis and polycondensation of organosilicium compounds. 

Porous inorganic materials, in general, and porous silica in particular, are very popular supports widely used in chromatography. Therefore, development of silica monoliths followed closely to that of the organic polymers. Detailed accounts of these materials have also been published several times. Separations using these monolithic separation media have also been treated theoretically. ... 

Phase separation (mixed organic and inorganic phases) Silica monoliths Hierarchical (micro, meso, macro)... 

In recent years, the interest in using porous silica and polymer-based monolithic stationary-phase media for ion chromatographic separations of inorganic and organic ions has increased.As compared to particle bed columns, monolithic columns represent a single piece of porous cross-linked polymer or porous silica. Monoliths are made in different formats as porous rods, generated in thin capillaries or made as thin membrane or disks. 

Pauli and co-workers [5, 6] used a very short (10 mm x 4 mm) coated silica monolith for the separation of inorganic anions. The back pressure was sufficiently low that a peristaltic pump could be used to pass eluent through the system. 

Caffeine, theophylline Beverages CEC organic-inorganic hybrid silica monolith C18-sulfonic groups using a mobile phase containing 25 mM phosphate-borate (pH 8)-acetonitrile (40 60, v/v) UV at 254 run [105]... 

Hou C-Y, Ma J-F, Tao D-Y, Shan Y-C, Liang Z, Zhang L-H, et al. Organic—inorganic hybrid silica monolith based immobilized titanium ion affinity chromatography column for analysis of mitochondrial phosphoproteome. J Proteome Res 2010 9 4093-101. 

Scheme 10.14 Scheme ofthe organic-inorganic hybrid silica monolithic matrix formation (a) and trypsin immobilization (b) [128], Source Copyright 2008 American Chemical Society. 

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