Use in capillary columns

Table 9.1.1. Column selection guide for stationary phases used in capillary columns...

Chirasil- Val is a unique chiral phase used in capillary columns for the separation of optical enantiomers. Most amino acids and many drugs containing polar functional groups may be resolved. 

Solvent modifiers and additives can be used to adjust the retention and selectivity of separation in packed-column SFC. Similar effects have been reported with open-tubular capillary SFC. The advantage of capillary column over packed column arises from the differences in permeability. Pressure ramps are much easier to use in capillary columns to modify the solvent strength (via density modification) as compared to packed columns. Therefore it should be entirely feasible, with capillary SFC, to combine the benefit of solvent density (pressure) programming with simultaneous modification of the solvent strength. ... 

Gas chromatography is often divided into categories based on the type of stationary phase used. Gas-liquid chromatography (GLC) implements a porous, inert solid support that is coated with a viscous, nonvolatile liquid phase. On the other hand, gas-solid chromatography (GSC) uses a solid adsorbent as the stationary phase. Klee offers these general rules-of-thumb for selection of stationary phase materials use solid adsorbents to separate room-temperature gases, liquid stationary phases to separate room-temperature liquid and solid mixtures, polar phases for polar solutes, and nonpolar phases for nonpolar solutes. Table 1 lists common liquid- and solid-stationary phase materials available for use in capillary columns. Barry cross-refers numerous column materials from nine different manufacturers. ... 

Note that natural organic adsorbents can also be used in capillary columns. Figure 3 shows the results of the separation of organic acids of natural origin on a natural polymer, Staphylococcus aureus cells. A fairly satisfactory degree of separation was achieved. The use of natural adsorbents seems promising. 

Other special columns are listed in Table 5.5. Most are available commercially in packed columns. Chiral packings are another important type they are more often used in capillary columns and they are discussed in Chapter 10. 

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. 

Graphite-Vespel (15% 85%) 350°C upper temperature limit general-purpose use in capillary columns recommended for MS or oxygen-sensitive detectors, also compatible with other detectors, such as FID and NPD most reliable leak-free connection proper installation requires a finger-tight turn on the nut, then an additional quarter-turn with a wrench the ferrule hole must match the column o.d. exactly to ensure a leak-free seal not reusable. 

NTE materials have also been used to control surface flaws. For example, Ti02, which has an NTE coefficient, can be deposited on the inside and outside of silica tubes used in capillary columns, so that when heated, the Ti02 contracts, causing a compression and, therefore, reducing propagation of surface flaws (Berthou et al. 1993). 

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