High performance silicas

C. E. Poole and M. T. Belay, The influence of layer thickness on the cliromatographic and optical properties of high performance silica gel tliin layer cliromatographic plates , J. Planar Chromatogr. 4 345-359 (1991). 

Recent advances in column stationary phases are remarkable. High performance silica-based reversed-phase 3 to 5 jxm packing materials have been developed for biological sample separations... 

Plates. High performance silica gel (10 x 20 cm) with fluorescent indicator and concentration zone (see Reagent Appendix). 

The USP 24/NF 19, section 201 (Ref.f p. 1856), contains a general TLC identification test that involves a non-high-performance silica gel layer with fluorescent indicator, chloroform-methanol-water (180 15 1) mobile phase, and detection under 254 nm UV light for verification of the identities of compendial drugs in dosage form test solutions prepared according to the individual monographs. Section 621 of the USP 24/NF 19 (Ref. pp. 1916-1917) presents brief information... 

Some contributions cover the development of specific materials and analytical methods to measure the characteristic properties of solid particles, such as particle sizes, surfaces areas, mechanical strengths, or solid-matrix interactions. Thus, papers from M. Heinematm and S. Hild deal with the characterization of silica-polymer interactions using Scanning Force Microscopy, while C. Panz uses the combination of special basic silica, fitting silanes, and adequate hydrophobization conditions to generate high-performance silica with new properties. 

Through the combination of special basic silicas, suitable silicone elastomers, and adequate hydrophobization conditions, it is possible to generate high-performance silicas with new properties at competitive prices. 

Layer Channeled preadsorbent high-performance silica gel. 

P. Moller, High Performance Silica for Preparative Chromatography Important Characteristics and Some New Applications, in Proceedings of Eurolech 98, Preparative el Process Scale Separations,... 

Cremers J (2008), Translucent high performance silica-aerogel insultation for membrane structures. Detail, English Edition, issue 4-2008, pp. 410-412 Cremers J (2009), Integration of photovoltaics in membrane structures. Detail Green, issue 1-2009, pp. 61-63... 

M. Nystron, W. Hermann, D. Sanchez, and P. Moller, Kromasil, a New High Performance Silica for Liquid Chromatography, EKA Nobel, S-44501, Suite, Sweden. 

Combining silanes with silica led to high-performing silica-filled rubber compounds. Organofunctional silanes with polysulfane groups such as bis-(3-(triethoxysilyl)propyl)tetrasulfane (TESPT) and bis-(3-(triethoxysilyl)propyl)disulfane (TESPD) (Fig. 12) are utilized to improve dispersability of silica in the rubber matrix. 

High-performance silica is used in high-performance thin-layer chromatography (HPTLC). HPTLC differs from normal TLC in that the size of the absorbent (usually silica) is only 5 pm, with a narrow distribution. This enables HPTLC to give better separations compared with TLC, which uses a standard silica, and, moreover, HPTLC requires a smaller sample size and has a lower detection limit compared with conventional TLC. HPTLC plates of varying sizes are commercially available and of late have found considerable applications in the field of lipids. Weins and Hauck (1995), in their survey of TLC, conclude that the use of HPTLC plates increased by 30% over the period 1993-95. An excellent application of HPTLC is illustrated in Fig. 1.1 for the separation of neutral and complex lipids. Yao and Rastetter (1985) have achieved separation of more than 20 lipid classes of tissue lipids on HPTLC plates using four developing solvents. 

Aloisi, J. D., Sherma, J. and Fried, B. (1990) Comparison of mobile phases for separation and quantification of lipids by one-dimensional TLC on preadsorbent high performance silica gel plates. Journal of Liquid Chromatography, 13, 3949-72. 

Figure 10.7 HPTLC separation of 1, acetophenazine 2, perphenazine 3, trifluoroperazine 4, promazine 5, thioridazine and 6, chlorpromazine on a high-performance silica gel plate using multiple development in the mobile phase benzene-acetone-ammonium hydroxide (80 20 0.2). [Reproduced with permission of The American Association for Clinical Chemistry from Fenimore et al. (1978).]...

Norfolk, E., Khan, S. H., Fried, B., and Sherma, J. (1994). Comparison of amino acid separations on high performance silica gel, cellulose, and C-18 reversed pha.se layers and application of HPTLC to the determination of amino acids in Biomphalaria glahrata snails. J. Liq. Chromatogr. 17 1317—1326. 

Unidimensional TLC of nucleic acid derivatives has also been done on silica gel. Issaq et al. (1977) separated mixtures of alkylated guanines, adenines, uracils, and cytosines on silica gel 6OF2S4, in various chloroform-alcohol solvent systems. The addition of 1 ml of ammonium hydroxide to the mobile phase prevented streaking and resulted in nondistorted developed spots. Figueira and Ri-beiro (1983) separated adenine, adenosine, inosine, hypoxanthine, 2-AMP, 5-AMP, ADP, ATP, cAMP, and dibutyryl cAMP also on silica gel 6OF254, and Sleckman et al. (1985) used conventional and high-performance silica gel to separate four representative nucleotides and their corresponding nucleosides. Detailed Experiment 2 of this chapter describes a unidimensional separation of nucleotides and nucleosides on silica gel. 

Brinkman and deVries (1979, 1980) also described TLC applications of drugs on high-performance silica gel plates. Numerous separations of pharmaceuticals on Whatman HPTLC plates and a useful list of references of drugs separated by HPTLC have been presented in the Whatman TLC Technical Series, Volume 2. 

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