Chromatographic Column Packings

As an adsorbing surface of silano) groups or through other polar, nonpolar, or ion-exchanging organic groups attached to the surface. 

As a sponge to hold a static liquid phase which is the active adsorbent. 

As a microporous packing of uniform pore size into which smaller molecules can diffuse rapidly, slightly larger ones more slowly or not at all, that is, size exclusion chromatography for determining molecular weight distribution of polymers. 

Each of these requires silicas of special structural characteristics, but in general the following applies. 

The powder particles should be spherical to permit uniform packing of uniform size to ensure uniform flow across a column cross-section of a size, usually in the range of 5-50 microns, to obtain maximum efflcien 7 within the limits of practical pressure drop through the column and with a uniform porosity and optimum structure for the particular type of use. 

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Chromatographic columns packed with conventional porous particles meet these requirements only to a limited extent. Slow diffusion of large molecules limits the speed of the separation due to the low rate of intraparticle mass transfer [7]. New approaches have been introduced to overcome this problem including ... 

In the case of chromatographic columns packed with spherical nonporous adsorbent particles the differential mass transfer balance can be described by... 

The technique of Gel Permeation Chromatography (GPC) was Introduced by Moore and Hendrickson (1,2 ) in 1964 for determining molecular weight distributions of polymer samples. The chromatographic column packings used for this new technique consisted of porous spheres of crossllnked styrene-divlnyl benzene resins (37-75ym) that were subsequently available as a family of columns under the name Styragel. Analytical column dimensions were 7.8 mm I.D. X 4 ft (122 cm). 

G. Molecular Sieves Chromatography. It is a method of separation using chromatographic columns packed with "molecular sieves (Refs 58, 78 82a). Molecular sieves are solid materials possessing a very high sorption ability (for small molecules), because they... 

Chromatographic System - Typically, a high-pressure liquid chromatograph, operated at room temperature, is fitted with a 30-cm x 4-mm stainless steel column packed with chromatographic column packing L3. An ultraviolet detector that monitors absorption at the 254-nm wavelength is used. 

To a chromatographic column, packed with 6.67 g of charcoal ("Nuchar C") with layers of sea sand at either end, 75 ml of acetone was added to wet the carbon. The column was heated to 40°C, and 25 ml of acetone was drained off. A solution of 20 g of dry crude dehydrocholic acid in 500 ml of acetone was poured into a reservoir atop the column and maintained in this reservoir at 40°C. This solution was then allowed to drop through the column at a constant rate over a 3-hour period. The column was then washed with 250 ml of acetone flowing through the column at a constant rate over a 1-hour-period at 40°C. The column effluent and wash acetone were combined and concentrated to a residual volume of about 100 ml which resulted in the formation of a thick slurry. The slurry was cooled with stirring at 0° to 5°C and aged for 30 min at this temperature. The slurry was filtered and the filter cake washed with cold acetone. The filter cake of U.S.P. dehydrocholic acid was sucked partially dry on the filter and then dried at 110°C for 3 hours. 

The extract is dissolved in 10 ml of dichloromethane and transferred to a 19 mm i.d. X 300 mm glass chromatographic column packed as follows 15 ml of 10% deactivated Florisil (10 ml H O + 90 grams Florisil) followed by a 2 cm layer of sodium sulfate which has been prewashed in order with 50 ml methanol, 50 ml acetone, and 50 ml dichloromethane. The sample flask is rinsed twice with additional 10 ml and 5 ml portions of dichloromethane, which are transferred to the column. When the solvent has reached the top of the sodium sulfate, the flask is rinsed with two 15 ml portions of acetone which are then transferred to the column. The solvent is allowed to drain to the top of the sodium sulfate layer. These washes are discarded. A 200 ml volume of methanol is added to the column to elute the TPTH, which is collected in a flask. The methanol is evaporated to dryness on a rotary flash evaporator. 

Stable esters coming formally from alkynols and carboxylic, sulphonic or dialkyl phosphoric acids were prepared for the first time via alkynyliodonium salts with the corresponding anion. Several alkynyl carboxylates were obtained by anion exchange of alkynyl iodonium tosylates the initially formed salts, PhI+C=CR RCO2, were converted spontaneously into the esters on elution through a chromatographic column packed with an anion-exchange resin (Pol+ArCOj) ... 

A velocity of 4 cm/s is maintained by a pressure drop of 2 psi in a gas chromatographic column packed with spherical particles of diameter dp = 0.01 cm. What pressure drop would you expect to use to reach the same velocity if the glass beads were of diameter 0.02 cm, everything else being constant ... 

A liquid chromatographic column packed with 5.00 fim diameter solid support particles and having a porosity e = 0.400 is found to have a flow resistance parameter 750. Calculate the specific permeability K0. Assume that the flowrate/pressure drop relationship is identical to that of a bundle of identical parallel capillaries whose axes are spaced (in a square cross-sectional array) a distance of 5.00 /im from one another. What is the single capillary diameter of the hypothetical bundle ... 

Kohler and Kirkland noted that for chromatographic column packings analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and chromatographic behavior, silica appears to possess associated and isolated surface silanol groups [ I9. The associated silanol (possessing weak-acid characteristics) is identified with a silanol hydrogen-bonded to its nearest neigh-... 

Lindsey [3] prepared phosphono-substituted porphyrin derivatives, (II), for attachment to metal oxide surfaces for use as a chromatographic column packing agent. Surface separation methods using 9-borabicycIo[3.3.I]nonane derivatives, (III), are described by Lindsey [4]. 

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