Coatings, silica

Capillary Columns Capillary, or open tubular columns are constructed from fused silica coated with a protective polymer. Columns may be up to 100 m in length with an internal diameter of approximately 150-300 )J,m (Figure 12.17). Larger bore columns of 530 )J,m, called megabore columns, also are available. 

Capillary Tubes Figure 12.42 shows a cross section of a typical capillary tube. Most capillary tubes are made from fused silica coated with a 20-35-)J,m layer of poly-imide to give it mechanical strength. The inner diameter is typically 25-75 )J,m, which is smaller than that for a capillary GC column, with an outer diameter of 200-375 )J,m. 

Clearly the best protection from oxidation by a silicide as a coating on a reactive substrate would be the disilicide, which has the highest silicon content, and could be expected to provide a relatively protective silica coating. 

Porous silicas coated with N-VP — AC copolymer may be used as an activated support for the immobilization of the biospecific ligands [50] or for the synthesis of hydrophobic adsorbents [54]. 

Jervis used porous silica coated with chemisorbed polyacrylhydrazide for immobilization of adenosine monophosphate (AMP) [117]. After periodate oxidation of its ribose residue the ligand was coupled to the carrier and used for isolation of lactate dehydrogenase from rabbit muscle. The specific capacity was 2 mg of protein/g adsorbent with a ligand content of 10 pmol/g, whereas recovery of enzymatic activity after elution was 85%. Hipwell et al. [118] found that for effective binding of lactate dehydrogenases on AMP-o-aminoalkyl-Sepharose the spacer arm length required at least 4 methylene links. Apparently, a macromolecule of polyacrylhydrazide acts itself like an extended spacer arm and thus allow AMP to bind the enzyme. 

Pal B, Torimoto T, Iwasaki K, Shibayama T, Takahashi H, Ohtani B (2004) Size and structure-dependent photocatalytic activity of jingle-beU-shaped silica-coated cadmium sulfide nanoparticles for methanol dehydrogenation. J Phys Chem B 108 18670-18674... 

Because a wide variety of TLC plates are available commercially, the most appropriate type of plate should be chosen considering several important factors such as the efficiency of the resolution of the lipid species of interest, cost of the plate, the size of the sample to be applied on the plate, and commercial availability of PTLC, depending on the amount of material to be separated. Silica plates are most commonly used for the analysis of hpids. If a large amount of sample material is needed to be separated, plates with a thicker layer of silica should be used. Commercial PTLC plates are available, and thicknesses of 200 to 2000 pm and 250 to 1000 pm are most commonly used in PTLC. Silica-coated glass plates can be of various sizes ... 

Coradin, T., Mercey, E., Lisnard, L. and Livage, J. (2001) Design of silica-coated microcapsules for bioencapsulation. Chemical Communications, 2496-2497. 

A.K. McEvoy, C.M. McDonagh and B.D. MacCraith, Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive ruthenium complexes immobilized in sol-gel-derived porous silica coatings, Analyst, 121(6) (1996) 785-788. 

Selvan ST, Tan TT, Ying JY (2005) Robust, non-cytotoxic, silica-coated CdSe quantum dots with efficient photoluminescence. Adv Mater 17 1620-1625... 

The ion-exchangers used in LC consist either of an organic polymer with ionic functional groups, or silica coated with an organic polymer with ionic functional groups. The types of functional groups used are the same as described in Chapter 18. Since IEC can be carried out with an aqueous mobile phase near physiological conditions, it is an important technique in the purification of sensitive biomolecules such as proteins. 

Whitsitt, E.A., et al., LPD silica coating of individual single walled carbon nanotubes. Journal of Materials Chemistry, 2005.15(44) p. 4678-4687. 

Whitsitt, E.A. and A.R. Barron, Silica Coated Single Walled Carbon Nanotubes. Nano Letters, 2003. 3(6) p. 775-778. 

TLC. Aliquots of samples and standards were run on silica-coated thin layer chromatography (TLC) plates in either n-butanol/acetic acid/water (4 1 1 by vol. (BUOH/HAC/H2O)) or n-propanol/concentrated ammo-nia/water (8 1 11, pre-equilibration). These eluents were previously described (Keller et ah, 1984) for the two-dimensional TLC-separation of elastin cross-links. 

Chromatographic resolution is also dependent on column efficiency (i). Column efficiency is directly dependent on the nature of the support matrix and how well that support is packed in its column. Available chromatographic supports are based on dextran, agarose, polystyrene, acrylic, cellulose, silica gel and a variety of other polymers. Althou cellulosic supports are manufactured in both microcrystalline and leaded forms, most supports are beaded. Newer supports may use hybrid bead construction where the base support is coated with a second materid (e.g., dextran or silica coated with agarose). 

Figure 16. Flowcell reactor constructed from silica coated aluminium plates sealed with a viton spacer [35],...

Jackson, T. and Clark, J.H. and Macquarrie, D.J. and Brophy, J. H. (2004). Base catalysts immobilised on silica coated reactor walls for use in continuous flow systems. Green Chem., 6, 193-195. 

Chen, R. and Li, Z. (1993). A study of silica coatings on the surface of carbon or graphite fiber and the interface in a carbon/magnesium composite. Composites Sci. Technol. 49, 357-362. 

Aliev, F.G. Correa Duarte, M.A. Mamedov, A. Ostrander, J.W. Giersig, M. Liz-Marjan, L.M. Kotov, N.A. (1999) Layer-by-layer assembly of core shell magnetite nanoparticles Effect of silica coating on interparticle interactions and magnetic properties. Adv. Mater. 11 1006-1010... 

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