Solid supports Chromosorb

Column conditions length, 1.8-m X 4-mm glass solid support, Chromosorb W, 80-100 mesh injector, 240°C column, 200° C detector, Ni, 310° C flow rate, 80-100 ml/min... 

Solid support Chromosorb P Chromosorb P Chromosorb P Chromosorb P Chromosorb P Capillary Chromosorb P... 

The separation of the alcohols is effected by the retention, to a varying degree, of the different alcohols by the liquid stationary phase (PEG20M) coated onto a solid support (Chromosorb W—ratio 10 90, respectively). The small differences in the physical properties and structure of the alcohols are sufficient to cause differences in the association (H bonding, dipole-dipole interaction, etc.), between the liquid stationary phase and the alcohol (solute) molecules. Thus, the compound having least association is eluted first, followed by the others in order of the degree of the association. The retention time (the time from injection to peak maxima) is a characteristic of the compound under the conditions used. 

Preliminary studies into a third variable, the partial pressure of water vapor in the system, are discussed in Part 3 of the Results and Calculations section. Each calorimetric sample ( 1 g, 13.47 mass % bitumen) came from a large sample of "reconstructed" oil sand consisting of Athabasca bitumen loaded onto a chemically inert solid support material (60/80 mesh acid washed Chromosorb W) of well-defined particle size. 

Packed columns contain an inert and stable porous support on which the stationary phase can be impregnated or bound (varying between 3 to 25%). The solid support is made of spheres of approximately 0.2 mm in diameter, obtained from diatomites, silicate fossils (such as kieselguhr, tripoli) whose skeleton is chemically comparable to amorphous silica. These materials, which have a specific surface area ranging from 2 to 8 m2/g, have been commercialised by several companies such as Johns Manville, under the name of Chromosorb , and are used universally. Other synthetic materials have been developed such as Spherosil , made of small silica beads. All of these supports have a chemical reactivity comparable to silica gel because of the presence of silanol groups. 

The d/l enantiomeric ratios for alanine, glutamic acid, and leucine are obtained by a gas chromatographic method (29), using the remaining half of the desalted amino acid fraction. The N-trifluoroacetyl-L-prolyl-DL-amino acid methyl esters are synthesized, and separation is performed on a Hewlett-Packard model 5711A gas chromatograph with flame ionization detector and a 20-ft column using 8% SP 2250 coated on Chromosorb W-AW-DMCS solid support. 

Parker and Kirk (P2), in 1961, attempted the GLC separation of barbiturates as the free acids, using a solid support of acid-washed firebrick (apparently unsilanized). They found that the retention time varied with sample size. In a later article, Parker et al. (P3) described the use of acid-washed Chromosorb W coated with either 5% SE-30 or 1% Carbowax 20 M in an attempt to provide a gas chromatographic screening procedure for barbiturates, alkaloids, sympathomimetic amines, and tranquilizers. Their conditions probably represent a compromise, with the result that their column was not necessarily the best that could have been prepared for resolution of mixtures containing only barbiturates. 

The function of the solid support is to act as an inert platform for the liquid phase in the column. Solid supports most often used are made either from diatomaceous earth or firebrick (clay). The Chromosorbs are the most common and are of various compositions. There are several types A, G, P, W, R, and T. Most can be acid washed (A W) and/or silanized (S). 

The solid support for a liquid phase should have a high specific surface area that is chemically inert but wettable by the liquid phase. It must be thermally stable and available in uniform sizes. The most commonly used supports are prepared from diatomaceous earth, a spongy siliceous material. They are sold under many different trade names. Chromosorb W is diatomaceous earth that has been heated with an alkaline flux to decrease its acidity it is light iu color. Chromosorb P is crushed firebrick that is much more acidic than Chromosorb W, and it tends to react with polar solutes, especially those with basic functional groups. 

The polarity of Chromosorb P can be greatly decreased by silanizing the surface with hexamethyldisilazane, [(CH3)3Si]2NH. Ottenstein (Ref. 7) has reviewed the selection of solid supports, both diatomaceous earth and porous polymer types. 

The catalytic activities of acids and bases for Claus reaction were investigated by supporting these on Chromosorb-A (a relatively inactive gas chromatographic solid support) and other materials and obtaining the relative activities of these compounds for Claus reaction based on initial rates at 240°C. The experiments were carried out in a fixed-bed integral flow reactor using low partial pressures of reactants. Acidity did not enhance catalytic activity but the deposition of bases (1-8 wt %) induced a dramatic increase in the catalytic activity for Claus reaction. Attempts were made to measure the basicities of these catalysts and relate these to the observed catalytic activity for Claus reaction. 

Sample Analysis. For analysis via radio gas chromatography the irradiated sample mixture was quantitatively transferred into a greaseless injection loop by means of a 1-L mercury Toepler pump. The chromatography column consisted of 150 ft of 0.25-in. o.d. stainless steel beverage tubing packed with 30 wt % of the crotonic acid ester of H(CF2)8CH20H coated upon 30/40 ASTM mesh Chromosorb PA solid support. The column was operated at 273 K with a helium carrier gas flow rate of 25 cm min" (NTP). 

Uronic adds may be identified and determined by reduction to the alditols and conversion thereof into alditol acetates. An acid commonly encountered in glycuronans is 4-O-methyl-n-glucuronic acid, but, on an ECNSS-M column, 4-O-methylgludtol and galactitol acetates are not well separated however, they are cleanly resolved on butanediol succinate. In some instances, the degree of separation achieved with ECNSS-M may be markedly influenced by the nature of the solid support used. Thus, this liquid phase on Chromosorb not add-washed may give longer retention-times, but improved resolution. ... 

The amount of liquid phase coated on the solid support varies with the support and can range from 1 to 25%. Table 5.3 shows that 15% liquid phase on Chromosorb P is a loading equivalent to nearly twice that amount (25.7%) on Chromosorb W due to their differences in density and surface... 

GLC results confirmed the presence of very slightly depressed levels of NPA after distillation in experiments 1-3 (Table 2). Analysis of experiment 4 by GLC was complicated, however, due to the hexanes introduced with TEA, which is used as a 25% solution in hexanes. The column used in the GLC analysis was the non-polar DC-200 (15%) on a Chromosorb P solid support. The more polar n-propyl alcohol elutes just prior to the elution of the non-polar (but lower boiling) hexane peak. The "hexane peak" is actually two peaks, probably corresponding to two structural isomers. The only problem with peak overlap occurs with the hexane peaks and an impurity intrinsic to Rohm and Haas MMA, possibly a reaction by product from the acetone-cyanohydrin process (ACH). Chromatogram (A) of Figure 3 shows the 1% NPA doped MMA prior to reaction with tri n-octyl aluminum (TOA). The peaks of interest are the air... 

Packed Columns. These columns are usually constructed of stainless steel tubing with diameters of 1 /8 in. (3 mm) or 1 /4 in. (6 mm) and lengths of from 4 to 12 feet. The column is packed with a liquid or low-melting solid as the stationary phase distributed on a solid support material. The stationary phase must be relatively nonvolatile, that is, it should have a low vapor pressure and a high boiling point. Some typical stationary phases used with packed columns are listed in Table 22.1. Typical support materials are shown in Table 22.2. The most common support material consists of diatomaceous earth (Chromosorb). 

Using Chromosorb N as solid support in SCOT columns... 

The stationary liquid phase is normally coated as a thin film on an inert solid support. The support is composed of small, uniformly meshed granules, so that a large surface area of the liquid phase is available for contact with the vapor phase to ensure efficient separation. Some common types of solid supports indude Chro-mosorb P and Chromosorb W, which are composed of diatomaceous earth. The surface areas of these supports vary from 1 to 6 m g- Columns are now commercially available with a wide variety of liquid phases on different solid supports. An alternative method of supporting the liquid phase is used in capillary columns. In these columns, the liquid is coated directly onto the inner walls of the tubing. These columns are highly efficient but relatively expensive. 

The most commonly used supports are derived from diatomaceous earth and tefion. They are sold under many trade names depending on their pretreatment. The diatomaceous earth supports may be either Firebrick derived materials, such as Chromosorb P (a form of crushed commercial firebrick) and Gas Chrom R, or materials derived from filter aids, which Include Chromosorb W (diatomaceous earth heated with an alkaline flux), Anakrom ABS, and Gas Chrom Q. Some other solid supports are known by the trade names Celite 545, Phasep P, Embacel etc., (ail diatomaceous earth derived). Table 11.5 lists properties of some principal types of solid supports. 

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