Silica layers, thin

When using the thin silica spacer layer, however, it was found that the results from the above-mentioned methods did not agree with the direct measurements from the Taly-surf profilemeter, as shown in Fig. 4(a). This was tentatively ascribed to the effect of penetration of the reflecting beam into the substrate. With a very thin silica layer, the depth of penetration and thus the phase change would depend upon the thickness of the silica spacer layer and also upon that of any oil film present. 

In order to verify the minimum number of carotenoids in an extract or fraction, a very easy and fast test can be carried out with only one small piece of silica gel thin layer plate, consecutively developed with 10% diethyl ether or 4% acetone in petroleum ether for carotene separation, followed by 70% diethyl ether or 15% acetone in petroleum ether for visualization of monohydroxy xanthophyll separation, and finally with 30% acetone in petroleum ether for separation of di- and trihydroxy-carotenoids. ... 

A considerable number of systems have been used to separate chlorophylls on thin layers [30,31]. The most readily applicable layers are prepared from cellulose, silica, or sucrose and use hydrocarbon carriers with a polar modifier, usually acetone, in the developing solvent. However, silica layers cause a level of decomposition that is unacceptable for preparative work. Sucrose layers offer no particular advantages in separation and are neither commercially available nor recommended. 

The latest innovation is the introduction of ultra-thin silica layers. These layers are only 10 xm thick (compared to 200-250 pm in conventional plates) and are not based on granular adsorbents but consist of monolithic silica. Ultra-thin layer chromatography (UTLC) plates offer a unique combination of short migration distances, fast development times and extremely low solvent consumption. The absence of silica particles allows UTLC silica gel layers to be manufactured without any sort of binders, that are normally needed to stabilise silica particles at the glass support surface. UTLC plates will significantly reduce analysis time, solvent consumption and increase sensitivity in both qualitative and quantitative applications (Table 4.35). Miniaturised planar chromatography will rival other microanalytical techniques. 

Ni et al. [143] investigated the profile of the major metabolites of primaquine produced by in vitro liver microsomal metabolism, with silica gel thin-layer and high performance liquid chromatography analysis. Results indicated that the liver microsomal metabolism could simultaneously produce both 5-hydroxyprimaquine (quinoline ring oxidation product) and carboxyprimaquine (side-chain oxidative deamination product). However, the quantitative comparative study of microsomal metabolism showed that the production of 5-hydroxyprimaquine was far much higher than that of carboxyprimaquine. 

Ni et al. [144] also investigated the profiles of major metabolites of primaquine produced from liver microsomal and mitochondrial metabolism, in vitro by silica gel thin-layer and reversed-phase high performance liquid chromatography. The results... 

Infrared spectra were obtained with a Perkin-Elmer 1800 and a Nicolet Magna-IR 750 FTIR spectrophotometer, and the absorption frequencies are reported in wave numbers (cm4). NMR spectra were obtained with BZH-300 and CA-F-300 Bruker FTNMR 300 MHz spectrometers. Chloroform-d was used as solvent, and all chemical shifts are reported in parts per million downfield (positive) of the standard. H-NMR and 13C-NMR chemical shifts are reported relative to internal tetramethylsilane, while 19F-NMR chemical shifts are reported relative to internal fluorotrichloromethane, Rf values were obtained from silica gel thin-layer chromatography developed with a mixture of 1.5 mL methylene chloride and three drops of acetone. The number of hydrate water molecules was calculated from the integration of H-NMR spectra. 

Silica gel thin-layer plates may be used to separate lipids on either a preparative or an analytical scale. They are sometimes used to fractionate the lipids into classes prior to removal from the plate and further analysis by GLC. In this case the appropriate area of silica gel is scraped off and the lipid extracted into chloroform or diethyl ether containing 1-2% methanol for simple lipids or into chloroform-methanol-water (5 5 1) for polar lipids. 

Ni thin films were used as catalysts by Jin et al. and Yan etal. to produce amorphous SiNW at 1200°C. No external supplies of Si were needed, but hydrogen gas was used. It was unclear whether the nanowires were amorphous silicon nanowires covered with silica layers, or silica nanowires. 

Merck 60 F254 silica gel thin-layer chromatography (TLC) plates... 

Finally the synthesis of inorganic-polymer composite membranes should be mentioned. Several attempts have been made to combine the high permeability of inorganic membranes with the good selectivity of polymer membranes. Furneaux and Davidson (1987) coated a anodized alumina with polymer films. The permeability increased by a factor of 100, as compared to that in the polymer fiber, but the selectivities were low (H2/O2 = 4). Ansorge (1985) made a supported polymer film and coated this film with a thin silica layer. Surprisingly, the silica layer was found to be selective for the separation mixture He-CH4 with a separation factor of 5 towards CH4. The function of the polymer film is only to increase the permeability. No further data are given. 

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. 

Place silica gel thin layer chromatogram plates on the shelves and run the normal process cycle. The TLCs are analyzed on their content of pump oil and refrigerant oil. 

TLC behavior of these samples observed with various single solvents on highly activated silica gel thin-layer are summarized in Table 6. From the table it is seen that carbon tetrachloride can distinguish chromatographically the 3,4-vinyl sample from either the cis-1,4 or the tram-1,4 sample. For separating the cis-1,4 sample from the tram-1,4 and 3,4-vinyl sample, binaries of (carbon tetrachloride + p-xylene) and (cyclohexane + p-xylene) were found to be effective. When the composition of these binaries was adequately adjusted, the cis-1,4 sample remained on the starting... 

Materials. The water used for all purposes was double-distilled (once with glassware) and deionized (final conductance was less than 1 X 10"6 ohm1 cm."1). Stearic acid (obtained from Sigma Chemical Co.) was at least 99% pure as determined by silica gel thin-layer chromatography (4), and the synthetic L-a(/ ,y-dipalmitoyl) lecithin was about 90% pure (see Ref. 13 for analysis). The ATP-14C and its derivatives were obtained from Nuclear-Chicago or New England Nuclear Corp. and were found to be 95-98% pure as determined by cellulose thin-layer chromatography (16). 

Figure 25-10 shows a rapid separation of proteins on superficially porous particles, which consist of a 0.25-p.m-thick porous silica layer on a 5-pm-diamctcr nonporous silica core. A stationary phase such as Clg is bonded to the thin, porous outer layer. Mass transfer of solute into a 0.25-p.m-thick layer is 10 times faster than mass transfer into fully porous particles with a radius of 2.5 pm. enabling high efficiency at high flow rate. Superficially porous particles are especially suitable for separation of macromolecules such as proteins, which diffuse more slowly than small molecules. 

Small funnel and qualitative grade fdter paper Silica gel thin-layer plates (20 X 20 cm and 5 X 10 cm)... 

Each column fraction is analyzed for lipid material by spotting on a 5 X 10 cm silica gel thin-layer plate and exposing it to iodine vapor as follows. Prepare seven tapered capillary tubes and use these to place a spot of each solution on the TLC plate. Put at least 10 capillary applications from a single fraction on a spot. Your final plate should then have seven spots, one for each fraction. Set the plate in an iodine chamber and allow it to remain for about 15 minutes or until some spots are yellow or red-brown. The presence of lipid in a fraction is indicated by the red-brown color. Retain all the column fractions that appear to have lipid. Each of these fractions will be analyzed in part B by thin-layer chromatography. 

---