Open column alumina

Indeed, great emphasis was placed on the presentation of compounds in crystalline form for many years, early chromatographic procedures for the separation of natural substances were criticized because the products were not crystalline. None the less, the invention by Tswett (3) of chromatographic separation by continuous adsorption/desorption on open columns as applied to plant extracts was taken up by a number of natural product researchers in the 1930s, notably by Karrer (4) and by Swab and lockers (5). An early example (6) of hyphenation was the use of fluorescence spectroscopy to identify benzo[a]pyrene separated from shale oil by adsorption chromatography on alumina. 

Because plants present chlorophylls and carotenoids simultaneously, it may be useful to separate both groups from each other in a laboratory or preparative scale in order to avoid contamination in further purification steps, mainly when they are prepared in large amounts. Clean-up procedures using an open column packed with absorbents such as alumina, magnesia, polyethylene powder, powdered sucrose, DEAE-Sepharose, starch, cellulose, or MgO HyfloSupercel are good approaches. MgO HyfloSupercel in a proportion of 1 1 or 1 2 is the usual adsorbent. Sucrose and cellulose are interesting as they do not alter the chlorophylls, but they are tedious to work with. 

Applications Open-column chromatography was used for polymer/additive analysis mainly in the 1950-1970 period (cf. Vimalasiri et al. [160]). Examples are the application of CC to styrene-butadiene copoly-mer/(additives, low-MW compounds) [530] and rubbers accelerators, antioxidants) [531]. Column chromatography of nine plasticisers in PVC with various elution solvents has been reported [44], as well as the separation of CHCI3 solvent extracts of PE/(BHT, Santonox R) on an alumina column [532]. Similarly, Santonox R and Ionol CP were easily separated using benzene and Topanol CA and dilaurylthiodipropionate using cyclohexane ethyl acetate (9 1 v/v) [533]. CC on neutral alumina has been used for the separation of antioxidants, accelerators and plasticisers in rubber extracts [534]. Column chromatography of polymer additives has been reviewed [160,375,376]. 

The more recent applications of open-column chromatography in fat-soluble vitamin assays utilize liquid-solid (adsorption) chromatography using gravity-flow glass columns dry-packed with magnesia, alumina, or silica gel. Such columns enable separations directly comparable with those obtained by thin-layer chromatography to be carried out rapidly on a preparative scale. 

The removal of sterols, vitamin E vitamers, carotenoids, and other interfering material from the unsaponifiable fraction of food samples has been achieved using one or more of the following techniques coprecipitation of sterols with digitonin (91), precipitation of sterols from a methano-lic solution (195,209), adsorption chromatography on open columns of alumina (70,91,96), thin-layer chromatography on silica plates (209), and solid-phase extraction on silica (68,100) and reversed-phase (210) cartridges. 

Liquid/Solid Chromatography (LSC) is adsorption chromatography. Adsorbents such as alumina and silica gel are packed in a column and the sample components are displaced by a mobile phase. Thin layer chromatography and most open column chromatography are considered liquid/solid chromatography. 

In open-column liquid chromatography, the test sample is added to the top of a column packed with adsorbent material (e.g. alumina, silica gel, polymer gel or fine-particle substrate coated with an organic compound). Differential movement... 

The liquid products were analysed by capillary gas chromatography (GC) and peak identifications were made with the aid of GC-MS used in conjunction with concentration of the aromatic species by open-column adsorption chromatography on alumina. To give a clear indication of the boiling point distribution of the products, the peaks in the chromatograms have been grouped using successive n-alkanes. This procedure could not be used as precisely for the n-hexadecane/quinoline mixtures because of overlap of the quinoline and product peaks close to Cu,... 

Open-column chromatography with silica gel and alumina is not applicable to the fractionation of tanins because of their strong binding to these adsorbents, which induces extensive loss of tannins. Such losses do not occur with countercurrent chromatography, as it does not use a solid stationary phase. Such molecules are very polar, so butanol-based solvent systems can be used. Centrifugal partition chromatography is more adequate in this case, as compared to hydrodynamic CCC, because of the good retention of the stationary phase of a such solvent system. 

HPLC. Many HPLC methods have been described in the literature (Hornero-Mendez and Minguez-Mosquera, 1998 Schoefs, 2002, 2003, 2004 Thompson et al., 2000). When the carotenoid composition is complex, as in passiflora fruit, which contains more than 10 carotenoids, it might be necessary to first separate the different groups of carotenoids. This can be done using an open column packed with alumina. Fraction 1, which contains carotenes and epoxi-carotenoids, is eluted with petroleum ether fraction 2, which is composed of monohydroxy- and keto-carote-noids, is eluted with 70-90% diethyl ether in petroleum ether and fraction 3, made up of polyhydroxy-carotenoids, is eluted with 0—30% ethanol in ether. The pigments contained in individual fractions can be further separated using particular TLC or HPLC methods (Mercadante et al., 1998). 

For samples with a high lipid content (e.g., milk), additional cleanup of the extracts may be necessary to eliminate other lipids such as triacylglycerols. In the past, open-column chromatography on magnesia, alumina, or silica gel has been used. More recently, solid-phase extraction (SPE) on disposable prepacked cartridges filled with silica or Cig reversed-phase packing material has been applied to vitamin A analysis. SPE is a refinement of the earlier open-column chromatographic systems. 

Adsorption chromatography is one of the more popular modern high-performance liquid chromatography (HPLC) techniques today. However, open-column chromatography and TLC are still widely used. - The adsorbents (stationary phases) used are silica, alumina, and carbon. Although some bonded phases have been considered to come under adsorption chromatography, these bonded phases will not be discussed. By far, silica and alumina are more widely used than carbon. The mobile phases employed are less polar than the stationary phases, and they usually consist of a signal or binary solvent system. However, ternary and quaternary solvent combinations have been used. 

Open-column chromatography on alumina or silica has been extensively used in surfactant analysis. It is inexpensive but tedious and is now being superseded by HPLC. 

Open-column chromatography usually employs either alumina or silica as sorbent and is gravity-driven. It does not require any specialised... 

GC assays of vitamin E have always suffered from the interference of cholesterol. A separation from a-tocopherol proved feasible on capillary columns and rarely on packed columns but at the expense of long analysis times. More commonly, cholesterol was exhaustively removed from saponified extracts using digitonin precipitation, open column chromatography on fiorisil, alumina or cel-ite-digitonin and TLC. Only capillary GC allowed to determine tocopherols (as their TMS ethers) in plasma using the simple solvent extraction approaches typical of LC assays. 

Naphthacene (benz[b]anthracene, 2,3-benzanthracene, rubene) [92-24-0] M 228.3, m >300 , 341 (open capillary), 349 , 357 . Crystd from EtOH or benzene. Dissolved in sodium-dried benzene and passed through a column of alumina. The benzene was evaporated under vacuum, and the chromatography was repeated using fresh benzene. Finally, the naphthacene was sublimed under vacuum. [Martin and Ubblehode J Chem Soc 4948 7967.] Also recrysts in orange needles from xylene and sublimes in vacuo at 186°. [UV Chem Ber 65 517 1932, 69 607 7956 IR Spectrochim Acta 4 373 7957.]... 

Figure 2.15 Separation of a mixture of saturated and unsaturated hydrocarbons on a 50 m x 0.32 mm fused silica porous-layer open tubular column coated with alumina modified wl potassium chloride. The separation was performed by temperature programming from 70 to 200°C at 3 C/mln. (Reproduced with permission fr

These have now been superseded by capillary columns, which offer greatly improved separation efficiency. Fused silica capillary tubes are used which have internal diameters ranging from 0.1 mm (small bore) to 0.53 mm (large bore) with typical lengths in excess of 20 m. The wall-coated open tubular (WCOT) columns have the internal surface of the tube coated with the liquid (stationary) phase and no particulate supporting medium is required. An alternative form of column is the porous-layer open tubular (PLOT) column, which has an internal coating of an adsorbent such as alumina (aluminium oxide) and various coatings. Microlitre sample volumes are used with these capillary columns and the injection port usually incorporates a stream splitter. 

The complex cis-Mo(CO)2(dppe)2 [l,2-ethanediylbis(diphenylphosphine)] is prepared by the literature method.8 In a dry box, a quantity (427 mg, 0.450 mmol) of this complex is mixed with NOPF6 (162 mg, 0.923 mmol). The NO[PF6] must be freshly prepared or from a freshly opened bottle. Dichloromethane (6 mL) is added and the mixture is rapidly stirred for 10 to 15 min until the solid has completely dissolved giving a green solution. This is eluted through a 5-cm column (diameter, 7 mm) of chromatographic alumina with dichloromethane. The bright yellow eluate is concentrated to a few milliliters by a water pump. Methanol (lOmL) is added and the mixture is cooled in an ice bath giving canary yellow crystals. These are filtered, washed with methanol, and dried in vacuo. Yield 260 mg (52%). 

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