Elution, chromatography

Elution development is by far the most common method of processing a chromatographic separation and is used in all types of chromatography. Elution development is best described as a series of absorption-extraction processes which are continuous from the time the sample is injected into the distribution system until the time the solutes exit from it. The elution process is depicted in Figure 1. 

It should be recalled that the distribution coefficients are referenced to the solvent mixture and not the stationary phase and are thus the inverse of the distribution coefficient employed in the chromatography elution equation. 

Figure 6A-C. High-performance anion-exchange chromatography elution profile of isolated modified hairy regions without addition of enzymes (A), with Biopectinase OS (B) and with rhamnogalacturonase-containing culture filtrate from an A. awamori multicopy transformant (C). /xC ftCoulomb- Data taken from Ref. 6.

Retention is usually measured in units of time for convenience. Voliime units are more exact. Table 1.1, after suitable corrections have been applied (26). Under average chromatographic conditions liquids can be considered incompressible, but not so for gases, and in gas chromatography elution volumes are corrected to a mean column pressure by multiplying them by the gas compressibility factor, j, equation (1.2)... 

General Procedure for the Formation of Benzene Derivatives (see Eq. 2.48) At 0°C, dimethyl acetylenedicarboxylate (284 mg, 2 mmol) and CuCl (198 mg, 2 mmol) were added to a solution of zirconacyclopentadiene (1 mmol) in THF, prepared in situ according to the known procedure [12]. The reaction mixture was then allowed to warm to room temperature and was stirred for 1 h. After hydrolysis with 3 n HC1, the mixture was extracted with diethyl ether. The combined extracts were washed sequentially with water, aq. NaHC03 solution, brine, and water, and then dried over MgS04. Concentration in vacuo followed by flash-chromatography eluting with a mixture of hexane and diethyl ether (10 %) afforded benzene derivatives. 

The crude material was purified using flash silica gel chromatography eluting with pentane/ether (3 1). This provided 0.31 g (85%) phenethanol. 

The crude product is dissolved in diethyl ether / petroleum ether (1 5) (5 mL) and poured onto a column (45-mm diameter) filled with 200 g of silica gel (Merck 230-400 mesh for flash chromatography). Elution (Note 23) under pressure (Note 14) with diethyl ether / petroleum ether (1 5) gives 2-oxo-5-methoxyspiro[5.4]decane as a colorless liquid (4.43 g 75%) (Note 24). 

The crude residue (15.2 g) was purified by silica gel column chromatography. Elution with hexane/ethyl acetate (10 1, 880 mL) gave 3-benzyloxy-2-methylpropene (13.9 g, 85.7 mmol, 92 %) as a colorless oil. 

L1p1d extraction with chloroform/methanol c1ean-up with column chromatography elution with acetonitrile, hexane and methylene chiori de. 

C, the solvent is evaporated, and the residue is treated with saturated aqueous NH4CI, extracted with ether, dried (MgS04) evaporated. The product is purified by Si02 column chromatography (elution with benzene/hexane, 9 1). 

Phenyl(alkyltelluro)acetylenes (general procedure) n-BuLi (1.35 M in hexane, 22.2 mL, 30 mmol) is added dropwise to phenylacetylene (3.10 g, 30.0 mmol) in THF (15 mL) at 0°C nnder N2. After stirring for 5 min at 0°C, elemental Te (3.90 g, 30.0 mmol) is added and the mixtnre reflnxed nntil the Te disappears ( 30 min). The heat source is removed and the alkyl halide (30 mmol) is added. The mixtnre is stirred for 40 min at room temperatnre, then dilnted with ether (60 mL), washed with brine and the layers separated. The organic phase is dried (MgS04), evaporated and the residne purified by Si02 flash chromatography (elution with hexane). 

Reductive detelluration of cyclic telluroethers (typical procedure) To a solution of 2,3-diliydro-2-[(phenylteUuro)methyl]benzofuran (0.338 g, 1 mmol) in toluene (6 ml.) is injected TBTH (0.67 ml, 2.5 mmol) at room temperamre, and the resulting solution is stirred under reflux for 1 h. The solution is evaporated under vacuum and the residual yellowish oil subjected to Si02 column chromatography (eluting with benzene/hexane, 3 1) to give pure 2,3-dihydro-2-methylbenzofuran as a colourless oil (0.128 g (95%) b.p. 93-94°C/23 torr). 

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