Silica particle

Natural colloid particles in aqueous systems, such as clay particles, silica, etc. may serve as carriers of ionic species that are being sorbed on the particulates (pseudocolloids). It seems evident that the formation and transport properties of plutonium pseudocolloids can not yet be described in quantitative terms or be well predicted. This is an important area for further studies, since the pseudocolloidal transport might be the dominating plutonium migration mechanism in many environmental waters. 

Adsorption chromatography using small particle silica or alumina has also been employed in the separation of biologically meaningful substances. Phospholipids, for example, have been separated on silica (38). One of the big problems for such substances is detection, since many of the compounds are not U.V. active. Generally, the refractive index detector is employed for isocratic operation, and the moving wire detector for gradient operation. Formation of U.V.-active derivatives is also possible (39). 

Another example of the use of small particle silica is in the analysis of theophylline in plasma, as shown in Figure 5 (40). The clean-up procedure is simply a single extraction of the plasma with an organic solvent. This analysis has also been achieved by reverse phase chromatography (41), and this points out the fact that in some separations (e.g. with components of moderate polarity) either the adsorption or reverse phase mode can be used. 

Several growth and formation mechanisms have been proposed for the formation of monodispersed Stober silica particles. Silica in general is an extremely well-studied system, and there are numerous publications with respect to the hydrolysis and condensation reaction. At present there are two major formation mechanisms that have been used to explain the formation of Stober silica particles. 

G Jones, HF DeLuca. High-pressure liquid chromatography separation of the metabolites of vitamins D2 and D3 on small-particle silica columns. J Lipid Res 16 448-453, 1975. 

R. Majors, High-performance liquid chromatography on small-particle silica gel,... 

R.M. Cassidy, D.S. LeGay and R.W. Frei, Study of packing techniques for small-particle silica gels in high-speed liquid chromatography, Anal. Chem., 46(1974)340. 

PTH-amino acids may be separated with a liquid-solid adsorption system consisting of small-particle silica gel (particle diameter, 5 pm) in a 50-cm column eluted with methylene chloride-dimethyl sulfoxide-rerr.-butanol in various ratios. The separation of a number of PTH-amino acids on Merkosorb SI-60 (5 pm) with methylene chloride-dimethyl sulfoxide-rerr.-butanol (125 0.1 1.0) is illustrated in Fig.4.3. Absorption is measured at 260 nm. Amounts of less than 1 nmole of each amino acid derivative can be... 

Engelhardt et al. [81] separated a number of DNS-animo acids by using small-particle silica gel and a mobile phase consisting of dichloromethane (saturated with water)-1% acetic acid-1% 2-chloroethanol. The separation of some DNS-amino acids under these conditions is shown in Fig.4.40. 

Fig.4.40. Separation of some DNS-amino acids on a small-particle silica-gel column (see text for details). Peaks 1 = inert 2 = unknown 3 isoleucine 4 = valine 5 = leucine 6 = tyrosine 7 = alanine 8 = tryptophan 9 = glycine 10 = histidine 11= lysine. (From ref. 81 with permission of the American Chemical Society, Washington.)...

The derivatives are extracted by adding 0.5 ml of hexane and shaking. An aliquot portion of the clear hexane layer is then spotted on to a TLC plate (silica gel) and eluted with solvents such as benzene-chloroform (1 1) or hexane-acetone (7 3). After separation, the plate is dried and sprayed until moist with 20% triethanolamine in isopropanol. The plate is dried and observed under UV light at long wavelength. The limit of detection is ca. 5 ng per spot. For HPLC, an aliquot portion of the hexane extract is injected into a system consisting of small-particle silica gel (7-18 fan) as stationary phase and hexane-chloroform (9 1) as the mobile phase. The limits of detection range from 1 to 5 ng per injection. 

Modern IEC. Improved stationary phases22 similar to those developed for the other types of LC have led to improved separations by IEC. The old resins described above were followed by pellicular resins that were much more efficient and incompressible but had lower capacities. As is the case in the other forms of LC, they have been largely replaced by small mi-croporous particles, silica and polymeric, that have the ionic groups directly on the particle or attached to a ligate or polymer on the particle surface. 

Figure 9.11. 5-MHz attenuation of US measurements at variable concentrations of samples A, B and C, corresponding to industrial particles, silica and sucrose, respectively. (Reproduced with permission of Elsevier, Ref [53].)...

Periodic nanoporous silicates have been prepared in a wide variety of conditions. Different sources of molecular, and non molecular silica have been used. This includes TEOS, TMOS, fumed, colloidal and precipitated silicas. Depending on the synthesis conditions, particularly on the nature of the silica source, crystallization may take place in seconds at subambient temperatures [82], or at room temperature [60,61,69,72,83]. However, in most cases the crystallization temperature was set in the 80 - 120 °C range. Liu et al. [84,85] found that the use of small amounts of colloidal particles (silica or titania) promotes the formation of ordered structures by providing nucleation seeds. The pH conditions varied from extremely acidic [60,61], to neutral [69,72] to very basic [48,49]. Ryoo and Kim [86]... 

In terms of availability, number, and nature of surface groups, surface area, pore size, pore volume, and form and size of the particles, silica has been undoubtedly the most preferred inorganic support. Suitable modification is possible via the surface silanol groups, which can react either directly with an appropriate metal complex or with an intermediate ligand group. Direct surface bonding has often been practiced, e. g., for the anchoring of metal carbonyl complexes [14] (eq. (11)), carbonyl clusters [26], polymerization catalysts [21, 62], or other special systems, e. g., 7r-allyl complexes [63] or metalloporphyrins [64]. 

Figure 16.17 shows the formation of conductive polymer/inor-ganic oxide nanocomposite particles. Silica, having a particle size of 20 nm, was dispersed in water, oxidant was added, followed by addition of monomer (pyrrole or aniline), and polymerization was conducted under constant stirring for 16 h at room temperature. Raspberry clusters of nanocomposite were ob-tained. ... 

In order to understand the theory of sorption in SPE, a simple understanding of (he solid phase is required. Typically the SPE sorbent consists of a 40- to 6()-pm silica particle (silica gel) onto which a liquid phase is chemically bonded. The silica gel cannot be used directly with aqueous solvent mixtures because the water deactivates the silica to such an extent that it has only weak interactions with most substances during the isolation process. So weak, in 25... 

Manufacturing of Large-Particle Silica Sols. A method for manufacturing silica sols consisting of large-diameter particles of 50-200... 

Microscopic - sized to Medium - sized Particle SILICA SOL... 

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