Open column chromatographic separation

In order to reduce the time-consuming open-column chromatographic processes, conventional methods of hydrocarbon-group-type separation have been replaced by MPLC and HPLC. Flash column chromatography is a technique less commonly applied than open-column version, but several applications have been described [2,24—27]. The common technique version is to use a silica-gel-filled column for example, 230 to 400 mesh 20 X 1 cm column size with a back pressure of 1.5 X 10 Pa of an ambient gas such as nitrogen. Solvents are similar to the ones apphed in the case of open-column chromatography fractionations. 

The reagents (15 mmol of each) were first dissolved in CH2C12, mixed with alumina, and heated in an open vessel to 60 °C. The reaction starts only after the solvent evaporates, and a 4 h reaction time is sufficient. Column chromatographic separation gave 380 mg (12.7% yield) of the crude product 1 along with 2 (<1% yield). 

Wallace, D, Henry, D. Pongar, K. Zimmerman, D. (1987). Evaluation of Some Open Column Chromatographic Methods for Separation of Bitumen Components. Fuel, Vol.66, No.l, pp. 44-50... 

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. 

The timely adoption of the cross-linked dextran gels (i.e., Sephadex) in late-fifties as a packing material for column chromatography opened an altogether new horizon of chromatographic separation whereby substances, in general, undergo separation more or less as per their molecular size. 

Equation (13) gives the minimum analysis time that can be obtained from an open tubular column, when separating a mixture of defined difficulty, under given chromatographic conditions. It is seen that, in a similar manner to the packed column, the analysis time is inversely proportional to the fourth power of the function (a-1) and inversely proportional to the inlet pressure. The contribution of the function of (k1), to the analysis time is not clear and can be best seen by calculation. It is also seen (perhaps a little surprisingly) that the analysis time is completely independent of the diffusivity of the solute in the mobile phase but is directly proportional to the viscosity of the mobile phase. 

Two principal GC-MS interfaces are available for open-tubular GC columns. The so-called direct interface provides the highest possible detector sensitivity, whereas the open-split interface offers the least possible interference with chromatographic separation. With the direct interface, the column exit is routed from the GC oven through a heated transfer line directly into the ionization chamber. As long as the vacuum-pumping system can remove the carrier gas and maintain a sufficiently low pressure, the MS detector will function. Also, little chance exists for adsorptive loses of solute because the analytes contact only the GC column. 

The need to measure concentrations in very small volumes is not restricted to biological systems. For example, open tubular columns for liquid chromatographic separations offer the advantage of increased resolution, but because their internal diameters may be as small as 15 pm, the amount of material in the eluted peaks is very small. Thus, the use of these columns requires detectors that can be used with low concentrations in small volumes. Jorgenson and co-workers showed that this could be accomplished by the insertion of a 10-pm-diameter, cylindrical electrode made from a carbon fiber into the end of the column [4]. The close fit between the column wall and the fiber ensured that a large fraction of the eluting molecules were electrolyzed. When the electrochemical data were collected in a voltammetric mode, the resolved compounds could be classi-... 

The use of UTEVA-Resin, an extraction chromatographic resin to be described in more detail below, has also been described for robotic separations of actinides in a glove box64-66 These authors designed their process to allow columns to run dry between steps to simulate what could happen in an unattended open-column process. In addition, corrosive solvents were avoided. They reported >90% recoveries and fractions that were suitable for thermal ion mass spectrometry (TIMS) source preparation without further purification or treatment. 

Gas chromatography and gas chromatography/mass spectrometry were employed to identify and quantitate individual molecular components. Both 25 and 50 meter glass support coated open tubular (SCOT) and fused silica wall coated open tubular (WCOT) capillary columns (SE.30, BP.l and BP.5 phases) were used with H2 as a carrier gas and F.I.D. detection. Acidic components were derivitized (BF3/methanol) to their methyl esters and hydroxyl groups to their silyl ethers (N,0-bis-(trimethylsilyl)trifluoroacetamide) in order to improve chromatographic separation. Carbon Preference Indices (CPI) were calculated using the equation -... 

Ethane-Deuteroethanes. Chromatographic separation of ethane and perdeuteroethane was first reported by Van Hook and Kelly (32) using packed columns loaded with methylcyclopentane at subambient temperatures. These authors also reported the partial resolution of protio-ethane from mono and di-deuteroethanes. The chromatographic properties of the perdeutero-ordinary system were further investigated on a variety of liquid substrates using packed column GLC techniques by Van Hook and Phillips (34) and on an open tubular etched glass column with a wetted wall (subsequently called wet glass in this paper) by Bruner, Cartoni, and Liberti (8). 

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