Silica porous glass

Common industrial inorganic supports are [14] silica, porous glass, alumina, zeolites, ceramics, Aerosil, and glass balls. Prior to its use the porous silica glass, for instance, must be modified as shown in Eq. 12 with amino alkoxy silanes [141. 

A conventional pulse catalytic microreactor was used with 15-65 mg of the catalyst for the cumene runs and 65 mg for the 2,3-dimethylbutane runs. The catalyst was held between 2 small plugs of borosilicate glass wool in a 5-mm ID diameter borosilicate reactor. In some experiments, the catalyst was diluted with 96% silica porous glass powder. The helium gas was purified by passage through alumina kept at liquid nitrogen temperature. The reaction temperature was measured by a thermocouple located adjacent to the reactor. The catalyst was pretreated at the desired temperature for 16 hours in a stream of helium. The products were analyzed with a dioctyl phthalate gas chromatography column at llO C. 

SiOj-based (silicates) Clays LDHs Zeolites MCM-41, MCM-48, FSM, PMOs Silica gel, precipitated silica, fumed silica Porous glasses (VPG, CPG), sintered glasses... 

It is important that the support material be stable under operational conditions with respect to mechanical forces, solvent temperature, pH, etc. A wide variety of different supports have been used for enzyme immobilization including natural polymers (cellulose, agarose diitosan), synthetic polymers (acrylic resins, styrene-divinylbenzene, polypropylene), and inorganic materials (silica, porous glass, Celite). Each offers advantages and disadvantages, and the optimal support for a given enzyme and reaction must be chosen individually. 

Fig. XVII-29. Nitrogen isotherms the volume adsorbed is plotted on an arbitrary scale. The upper scale shows pore radii corresponding to various relative pressures. Samples A, Oulton catalyst B, bone char number 452 C, activated charcoal F, Alumina catalyst F12 G, porous glass S, silica aerogel. (From Ref. 196).

PMMA, on the unmodified porous glass and silica gel, and the universal calibration curves for polystyrenes and poly(methyl methacrylates) did not coincide (10,12,19). 

The materials originally used as stationary phases for GPC were the xerogels of the polyacrylamide (Bio-Gel) and cross-linked dextran (Sephadex) type. However, these semi-rigid gels are unable to withstand the high pressures used in HPLC, and modern stationary phases consist of microparticles of styrene-divinylbenzene copolymers (Ultrastyragel, manufactured by Waters Associates), silica, or porous glass. 

Chromatographic Packings Prepared by Physical Adsorption of Polymers on Silica or Porous Glass... 

Silica or porous glass is usually used as the solid phase in oligonucleotide synthesis. The support is functionalized through an amino group attached to the silica surface. There is a secondary linkage through a succinate ester to the terminal 3 -OH group. 

Figure 11(A) shows a principle sketch of a SEC set-up. The eluent (solvent) is pumped at a constant flow rate through the system. A small amount of polymer solution (typically 200 pL) is injected manually or with an autosampler. The main part comprises a set of columns (typically 3-4 columns+pre-column) typically packed with microporous styrene-divinylbenzene, porous glass, or silica. In the routine analytical laboratory it is especially useful to have a pre-column in order to collect impurities that might be present in the samples. If many different samples are to be analyzed, it is necessary to check the reliability of the columns frequently to avoid artefacts due to residues from previous samples still held on the column. In order to avoid problems, samples should be purified before they...

Methyl radicals formed on a silica gel surface are apparently less mobile and less stable than on porous glass (56, 57). The spectral intensity is noticeably reduced if the samples are heated to —130° for 5 min. The line shape is not symmetric, and the linewidth is a function of the nuclear spin quantum number. Hence, the amplitude of the derivative spectrum does not follow the binomial distribution 1 3 3 1 which would be expected for a rapidly tumbling molecule. A quantitative comparison of the spectrum with that predicted by relaxation theory has indicated a tumbling frequency of 2 X 107 and 1.3 X 107 sec-1 for CHr and CD3-, respectively (57). 

The supports employed for covalent attachment of enzymes can be classified into two groups a) natural (agarose, dextran, cellulose, porous glass, silica, the optical fiber itself or alumina) and b) synthetic (acrylamide-... 

Zsolnay and Kiel [26] have used flow calorimetry to determine total hydrocarbons in seawater. In this method the seawater (1 litre) was extracted with trichlorotrifluoroethane (10 ml) and the extract was concentrated, first in a vacuum desiccator, then with a stream of nitrogen to 10 pi A 50 pi portion of this solution was injected into a stainless steel column (5 cm x 1.8 mm) packed with silica gel (0.063-0.2 mm) deactivated with 10% of water. Elution was effected, under pressure of helium, with trichlorotrifluoroethane at 5.2 ml per hour and the eluate passed through the calorimeter. In this the solution flowed over a reference thermistor and thence over a detector thermistor. The latter was embedded in porous glass beads on which the solutes were adsorbed with evolution of heat. The difference in temperature between the two thermistors was recorded. The area of the desorption peak was proportional to the amount of solute present. 

Porous glasses and silica gels with controlled pore sizes which are rigid... 

Sensors based on the above reaction scheme have been developed for Al3+, Zn2+, Cu2+, Ca2+, Pb2+, Hg2"1", K+, Li+, etc. A polycation, protamine sensor has also been developed using 2/7/-dichlorofluorescein octadecyl ester (DCFOE) doped in polymer membranes. However, most of these sensors are pH dependent due to the pH dependence of the cation complexation reactions. The cation ion indicators can be immobilized on any solid support, such as silica, cellulose, ion-exchange resin, porous glass, sol-gel, or entrapped in polymer membranes. 

Figure 9.1 Examples of texture of the materials formed on a short range from amorphous Si02 (a) silica gel (b) hydrothermally treated silica gel (c) porous glass (d) mesoporous mesophases type of MCM-41 and (e) opal.

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