Coated silicas

ALUMDIUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - HYDRATED] (Vol 2) Alumina-coated silica sols... 

Neon [7440-01-9] M 20,2, Passed through a copper coil packed with 60/80 mesh 13X molecular sieves which is cooled in liquid N2, or through a column of Ascarite (NaOH-coated silica adsorbent). 

Numerous applications of polymer-coated silicas to chromatography of biopolymers allow one to conclude that adsorbed or grafted hydrophilic nonionizing... 

It has been outlined by several authors that the single macromolecule may be irreversibly bound because of the large number of weakly interacting segments. The first papers on the construction of polymer-coated silica adsorbents involved the physical adsorption of water-soluble polymers. Polyethylene oxides [28, 29] and poly-/V-vinylpyrrolidone [30] are examples of the stationary phases of this type. 

Fig. 10. HPLC of proteins (commercial samples) on the /V-butyl polyacrylamide coated silica gel column. Sample 20 pi of 5-15 mg/ml protein solution in buffer A. Buffer A 10% methanol, 0.2 mol/1 ammonium acetate, pH 4.5. Buffer B methanol. Gradient 50-min linear, 0-100% B. Flow rate 0.8 ml/min. Peaks (/) — lysozym, (2,3) — insulin, (4,5) — myoglobin [57]...

Polyphosphazene Coated silica Magnesium oxide Antioxidants Peroxide... 

Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

Forgacs, E. and Cserhati, T., Use of principal component analysis for studying the separation of pesticides on polyethylene-coated silica columns, J.Chro-matogr. A, 797, 33-39, 1998. 

Yamauchi, S., Nimura, N., and Kinoshita, T., Protamine-coated silica gel as packing material for high performance liquid chromatography of carbohydrates, Analyst, 118, 161, 1993. 

Miyake, K. Kitaura, F. Mizuno, N., Phosphatidylcholine-coated silica as a useful stationary phase for high-performance liquid chromatographic determination of partition coefficients between octanol and water, J. Chromatogr. 389, 47-56 (1987). 

The silica microspheres provide some diversity but not enough for many complex discrimination tasks. To introduce more sensor variety, hollow polymeric microspheres have been fabricated8. The preparation of these hollow microspheres involves coating silica microspheres by living radical polymerization, using the surface as the initiation site. Once the polymer layer forms on the silica microbead surface, the silica core is removed by chemical etching. These hollow spheres can be derivatized with the dye of interest. The main advantage of these polymer microspheres is the variety of monomers that can be employed in their fabrication to produce sensors with many different surface functionalities and polymer compositions. 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

Radical polymerization of styrene was carried out in the presence of bare silica particles, and of the HPC-coated silica particles in water by using potassium persulfate as an initiator. Table 2 gives the typical ingredients used for these polymerizations. The HPC-coated silica particles were prepared under the same conditions as in the adsorption experiments. The polymerization temperature was kept at 1+5 °C to protect the adsorption layer of HPC, and polymerized for 2l+ hrs in the same manner as that... 

Samples Bare silica particles(wt %) HPC-coated silica particles(wt %) Styrene (mol/l) K2S2O8 (mol/l)... 

It was apparent that the dense adsorption layer of HPC which was formed on the silica particles at the LCST plays a part in the preparation of new composite polymer latices, i.e. polystyrene latices with silica particles in the core. Figures 10 and 11 show the electron micrographs of the final silica-polystyrene composite which resulted from seeded emulsion polymerization using as seed bare silica particles, and HPC-coated silica particles,respectively. As may be seen from Fig.10, when the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of silica particles, and indeed new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were generated. This indicated that the dense adsorption layer of HPC formed at the LCST plays a role as a binder between the silica surface and the styrene molecules. 

Figure 11. Electron micrograph of composite silica-polystyrene latex system, SPL(HPC), prepared by using HPC-coated silica particles as the seed.

The chiral recognition ability of the insoluble (+)-l was estimated by HPLC using a column packed with small particles of l.25 However, this column showed a poor efficiency because of a low theoretical plate number. This defect was overcome by coating soluble poly(TrMA) with a DP of 50 on macroporous silica gel.26 The 1-coated silica gel had higher resistance against compression and longer lifetime than the CSP of insoluble 1. Moreover, the two 1-based CSPs show quite different chiral recognition for several race-mates, which may be attributed to the different orientation of 1 in bulk and on the surface of the silica gel.27... 

The 1-coated silica gel has resolved more than 200 racemic compounds so far some of them are shown in Figure 3.6. The CSP is especially useful for the resolution of stereochemically interesting compounds without... 

In a laboratory study by Schlekat et al. [15], it was demonstrated that coating silica particles with an exopolymer prepared from an estuarine bacterium enhanced the sorption of cadmium on to the particles. The composition of the exopolymer was glucose, galactose and glucuronic acid in the ratio 5 2 1. These investigations also compared the effects of salinity, pH and different concentrations of cadmium. Increasing salinity resulted in less cadmium associated with the particles, presumably due to competition with the chloride ion. The pH had a dramatic effect, resulting in only ca. 10% absorbed at pH 5 to more than 95% at pH 9. 

On the other side, reversed-phase chromatography on non-polar supports (Ci, C2, C8, Cis, polyethylene-coated silica or alumina) is apparently unsuitable for the separation of different oligomers, because... 

C.W. Huck, M.R. Buchmeiser and G.K. Bonn, Fast analysis of flavonoids in plant extracts by liquid chromatography-ultraviolet absorbance detection on poly(carboxylic acid)coated silica and electrospray ionization tandem mass spectrometric detection. J. Chromatogr.A 943 (2002) 33-38. 

---