Silica fractions from

Purification of luciferin (Rudie etal., 1976). The luciferin fractions from the DEAE-cellulose chromatography of luciferase were combined and concentrated in a freeze-dryer. The concentrated solution was saturated with ammonium sulfate, and extracted with methyl acetate. The methyl acetate layer was dried with anhydrous sodium sulfate, concentrated to a small volume, then applied on a column of silica gel (2 x 18 cm). The luciferin adsorbed on the column was eluted with methyl acetate. Peak fractions of luciferin were combined, flash evaporated, and the residue was extracted with methanol. The methanol extract was concentrated (1 ml), then chromatographed on a column of SephadexLH-20 (2 x 80 cm) usingmethanol asthe solvent. The luciferin fractions eluted were combined and flash evaporated. The residue was... 

Systems with different selectivity were nsed for the separation of 10-deacetyl-baccatin III (10 DAB 111) from yew extracts [69]. A silica column with stepwise gradient elution with aqneous methanolic mobile phases can be nsed for separation of the taxoid fraction from nonpolar materials, partial separation of the taxoid fraction into a polar one (containing 10-DAB 111), and for a medinm polarity taxoid fraction (containing paclitaxel and cephalomannine). Most polar material (tannins... 

Also, different selectivity systems of were nsed for the separation of the alkaloid fraction from Corydalis solida herb. The extract was fractionated by the nse of a sihca layer elnted with 10% propanol-2 in dichloromethane (see Fignre 11.15a). Fraction 1 elnted dynamically from the adsorbent was rechromatographed by the nse of silica layer and eluent of higher strength containing acetonitrille + propanol-2 + acetic acid + dichloromethane. It enables the separation of the six zones of alkaloids from fraction I (see densitogram in Figure 11.15b). 

FIGURE 11.20 Densitogram of alkaloid fraction from Fumaria officinalis herb extract chromatographed in system silica/PrOH -i- AcOH -i- CHjClj (4 1 5) (a) fraction introduced with applicator with evaporation of solvent (b) fraction introduced from the edge of the layer with the eluent distributor. 

FIGURE 11.21 Densitograms of PLC of Taxus baccata fraction from preparative column (silica/aqueous methanol) containing unknown taxoid (Tax 1) introduced to the layer with a set of capillaries with simultaneous evaporation of solvent from the starting band. System silica/CH2Cl2 + DX + Me2CO + MeOH (84 10 5 1). Plates double developed (a) 0.3 ml of fraction introduced (b) 0.5 ml of fraction introduced (c) 1 ml of fraction introduced to the layer. 

Another variation of the preceding method is to apply HPLC to fractionate the cleaned-up aliphatic-aromatic fraction from flash colurim separation of soluble organic matter as it is performed in the Chevron laboratory, for example, as described in Reference 2. A Waters HPLC system equipped with a preparative Whatman Partisil 10 silica column (9.4 X 500 mm), a HPLC pump, and two detectors for separation monitoring (a UV and refractive index detector) are used, giving three fractions of aliphatic hydrocarbons, mono-, di-, and triaromatics and polar compounds. The hrst two fractions are eluted with hexane, whereas polar compounds are eluted with... 

Applications Sollinger and Sawatzki [793] have reported the use of TLC-Raman for routine applications, e.g. TLC of hydroxybenzenes (including hydro-quinone and pyrogallol) on conventional, silica gel and specific Raman-TLC plates (coated with spherical silica gel). Databases were used for identification of substances. Typical detection limits were in the low p,g region per application, Micro-Raman spectrometry has been employed in analysing TLC fractions from polymer additives within a detection limit... 

Simple and comprehensive 2D HPLC was reported in a reversed-phase mode using monolithic silica columns for the 2nd-D separation (Tanaka et al., 2004). Every fraction from the lst-D column, 15cm long (4.6 mm i.d.), packed with fluoroalkylsilyl-bonded (FR) silica particles (5 pm), was subjected to the separation in the 2nd-D using one or two octadecylsilylated (Cig) monolithic silica columns (4.6 mm i.d., 3 cm). Monolithic silica columns in the 2nd-D were eluted at a flow rate of up to lOmL/min with separation time of 30 s that provides fractionation every 15-30s for the lst-D, which is operated near the optimum flow rate of 0.4-0.8 mL/min. The 2D-HPLC systems were assembled, as shown in Fig. 7.6, so that the sample loops of the 2nd-D injectors were back flushed to minimize band broadening. 

An illustrative example is the work of Clark et al, on the conformation of poly(vinyl pyrrolidone) (PVP) adsorbed on silica 0). These authors determined bound fractions from magnetic resonance experiments. In one instance they added acetone to an aqueous solution of PVP in order to achieve theta conditions for this polymer. They expected to observe an increase in the bound fraction on the basis of solvency effects as predicted by all modern polymer adsorption theory (2-6), but found exactly the opposite effect. Their explanation was plausible, namely that acetone, with ability to adsorb strongly on silica due to its carbonyl group, would be able to partially displace the polymer by competing for the available surface sites. 

The complete oil fraction from FT synthesis was treated over bauxite, a natural silica-alumina, at a temperature around 400°C. This bauxite treatment step was a commercial process, called the Perco process, which was used as a sulfur removal step in oil refineries. The acid-catalyzed conversion of the syncrude over bauxite... 

Prepare the lipid for chromatography by dissolving 50 to 75 mg of crude lipid in a minimum of hexane (5 to 10 mL). Open the stopcock and allow excess solvent to drain from the column until the level of solvent just reaches the top of the silica gel column. Very carefully add the solution of crude lipid to the top of the column. This should be done by using a Pasteur pipet and allowing drops of the solution to run down the inside of the glass column to the top of the silica gel bed. It is important not to disturb the top of the silica gel column. After addition of the lipid solution, begin to collect a fraction from the bottom of the column into a 25-mL Erlen meyer flask. Set the flow rate to about 2 drops per second. When the level of solution in the column reaches the top of the silica gel, turn off the stop-... 

A source of error in chemical analyses of montmorillonites (and in other clays) that is not commonly checked is the presence of amorphous material, particularly Si and Al. Table XXXII lists structural formulas given by Osthaus (1955) for montmorillonites which were purified by size fraction and by extraction with 0.5 N NaOH to remove amorphous Si and Al. In six analyses dissolved silica ranged from 3.6 to 8.4% and alumina from 0.6 to 2.25%. Amorphous silicon dioxide should be expected in most montmorillonites derived from volcanic material. The source glass has more Si than is required for the 2 1 layer and the excess must be leached from the glass. Much of the Si is deposited in the sediments underlying the bentonite bed in the form of chert but it is to be expected that the extraction would not be complete and a portion of the colloidal Si would remain in the bentonite bed. 

In an autoclave a mixture of 10.0 g of crude l,2-epoxy-3-[di-(2,6-xylyl)-methoxyjpropane and 100 ml of 25% ammonia in 300 ml of methanol is heated at 80°C for 5 h with shaking. The solvent is removed by evaporation and the residue (about 12.0 g) is dissolved in 10 ml of ethanol and the solution passed through a column filled with silica gel, which affords separation of the main fraction from the by-product. The solvent is removed by evaporation and the residue is crystallised from petroleum ether (boiling range 60-80°C). 5.7 g of the desired l-amino-3-[di-(2,6-xylyl)-methoxy]propan-2-ol are obtained in the form of colourless crystals, melting point 105-106°C. 

The fractions were filtered with a 5 ym filter apparatus (Millipore, Bedford, MA) to remove any silica originating from the preparative scale column. The fractions were then rotary evaporated to near dryness in tared round bottom flasks. These were subsequently dried overnight in a vacuum oven at 60°C and weighed. The hexane and toluene fractions were diluted to 5 and 20 mL, respectively, with CC14> Both fractions were totally soluble in this solvent as well as in THF. 

Function of Pre-HPLC Column. The schematic in Figure 6 for a HPLC chromatogram representative of extracts of agricultural products illustrates use of silica gel adsorption chromatography for the pre-HPLC cleanup step. The schematic shows that (A) a large part of the co-extractives can be removed in the first fraction from the precolumn, (B) the polarity of the mobile phase can be adjusted so the pesticide elutes in pre-HPLC column fraction B where the eluate can be collected and concentrated for injection into the HPLC, while (C) more polar compounds that would otherwise appear during HPLC have been eliminated by permanent adsorption on the pre-HPLC Column. 

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