Temperature packed column chromatography

Rein, H. T., Miville, M. E., Fainberg, A. H. Separation of oxygen and nitrogen by packed column chromatography at room temperature. Anal. Chem. 35, 1536 (1963). 

Relative retentions..the a values..usually vary Inversely with column temperature, but are most strongly affected by the choice of liquid phase. In packed column chromatography, the choice of liquid phase Is usually the most effective route by which separation efficiency Is Influenced. In capillary GC, however, there Is normally such an abundance of theoretical plates that the choice of liquid phase Is a relatively unimportant parameter for many analyses. In some cases however. It does become desirable (or even necessary) to select a liquid phase in which the relative retentions of certain solutes Is larger. Until quite recently, this posed a real problem with the fused silica capillary column, because the more polar liquid phases, l.e. those In which relative retentions are usually greater, coated fused silica only reluctantly, and produced columns whose useful lives were quite limited. The development of stable bonded phase columns ( ) eventually overcame this difficulty (vide Infra). 

Reaction Procedure (Scheme 2.51) CS2CO3 (0.77 mmol), Pd(OAc)2 (3 mol%), PCya HBF4 (6 mol%) and pivalic acid (30 mol%) were weighed in air and placed in a screw capped vial (4 mL) with a magnetic stir bar. The reaction vessel was evacuated and backfilled with argon (x3). The cyclization precursor (0.70 mmol) was then added to the reaction vessel as a solution in mesitylene (3 mL). The reaction was heated to 135 °C for 12 hours. Upon completion, the reaction was cooled to room temperature. The products were loaded directly onto a silica gel packed column chromatography and eluted using ether-hexane mixtures. 

Supercritical fluid chromatography is the name for all chromatographic methods in which the mobile phase is supercritical under the conditions of analysis and the solvating properties of the fluid have a measurable effect on the separation. SFC has some advantages over GC and HPLC it extends the molecular weight range of GC, thermally labile compounds can be separated at lower temperatures, compounds without chromophores can be sensitively detected, and the use of open-tubular and packed columns is feasible. SFC can be employed in both the analysis of natural pigments and synthetic dyes, however it has not been frequently applied in up-to-date analytical practice. 

Finally, supercritical fluid chromatography, in which a supercritical fluid is used as the mobile phase, was introduced by Klesper [164-166]. SFE directly coupled to SFC provides an extremely powerful analytical tool. The efficient, fast and selective extraction capabilities of supercritical fluids allows quantitative extraction and direct transfer of the selected solutes of interest to be accomplished to the column, often without the need for further sample treatment or cleanup. Extraction selectivity is usually achieved by adjusting the pressure of the supercritical fluid at constant temperature or, less often, by changing the temperature of the supercritical fluid at constant pressure. SFE coupled with packed column SFC has found... 

A fourth factor is the flow rate of the eluent (mobile phase). A too high rate decreases resolution because there is no time for molecules to diffuse into the pores of the matrix. In contrast, a very slow migration of solvent decreases the resolution by remixing the components by diffusion. The effect of diffusion is minimized if the chromatography is done at low temperature. If short separation times are necessary, pre-packed columns, elevated pressure, or HPLC columns are indispensable. 

Spectra of these tautomers were obtained on samples separated by gas chromatography from thioketo-thioenol mixtures. Trithioacetone pyrolysate was passed through a DC 200 silicone oil on Gas Chrom Z packed column. As the appropriate sample eluted from the column, it was condensed on a sodium chloride plate cooled to —100° C and its spectrum immediately determined. The very low temperature employed prevented loss of thioenol by tautomerization and of thioketo by polymerization. 

Direct vaporisation injection. For packed columns and megabore columns of 530 pm, which typically use a flow rate of 10 ml/min, direct vaporisation is a simple way to introduce the sample. All models of this type of injector are a variation of a simple assembly which uses a metal tube with a glass sleeve or insert. The glass insert is swept by the carrier gas and heated to the vaporisation temperature for the analytes undergoing chromatography. One end of the injector contains a septum made of silicone rubber that allows the syringe needle to pass through it into the system. The other end of the injector is connected to the head of the column (Fig. 2.4). The entire sample is injected into the column in a few seconds. 

Figure 24-10 Comparison of (a) isothermal (constant temperature) and ( >) programmed temperature chromatography. Each sample contains linear alkanes run on a 1.6-mm-diameter x 6-m-long packed column containing 3% Apiezon L (liquid phase) on 100/120 mesh WarAport 30 solid support with He flow rate of 10 mL/min. Detector sensitivity is 16 times greater in panel a than in panel b. [From H. M McNair and E. J. Bonelli, Basic Gas Chromatography (Palo Alto. CA Varian Instrument Division. 1968).]...

FLOW. The rate at which zones migrate down the column is dependent upon equilibrium conditions and mobile phase velocity on the other hand, how the zone broadens depends upon flow conditions in the column, longitudinal diffusion, and the rate of mass transfer. Since there are various types of columns used in gas chromatography, namely, open tubular columns, support coated open tubular columns, packed capillary columns, and analytical packed columns, we should look at the conditions of flow in a gas chromatographic column. Our discussion of flow will be restricted to Newtonian fluids, that is, those in which the viscosity remains constant at a given temperature. 

Samples of the reaction products were withdrawn out of the reactor at regular time intervals and analysed Dy gas chromatography. The conditions for the GC measurements were as follows a packed column (4m- 1/8") with 0V 210 10 % + XE 60 5 % on Chromosorb WHP 80/100 and column temperature isothermal at 110°C - Dodecane was used as a standard. 

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