Solid Stationary Phases GSC

As mentioned before, there are two common types of GC gas-liquid chromatography (GLC) and gas-solid chromatography (GSC), depending on the physical state of the stationary phase. GSC is seldom used. In GLC the analyte is partitioned between the mobile phase (gas) and a liquid phase, which is retained on an inert solid support. The liquid phase should ideally possess a low volatility (so that it does not volatilise with the analyte), be thermally stable and chemically inert, and have favourable solvent characteristics. 

The first reported use of a vapor as the mobile phase is attributed to Martin and Synge in 1941. They used the principles of partition chromatography, whereas James and Martin, in 1952, described the first application of this method, gas-liquid chromatography (GLC), for the analysis of fatty acids and amines. Gas adsorption chromatography (GSC), on the other hand, involves the use of a solid stationary phase and separation is based on an adsorptive mechanism. This technique was first described in 1947 in a doctoral thesis by Prior,under the supervision of Professor Cremer, and subsequently in their 1951 publication.f ... 

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. ... 

In adsorption chromatography, also known as GSC (gas-solid chromatography), the components are adsorbed on a solid, stationary phase. The stationary phase can consist of such materials as active carbon, silica gel, molecular sieves, aluminum oxide, or Porapack. 

In gas-solid chromatography (GSC) the stationary phase is a solid adsorbent, such as silica or alumina. The associated virtues associated therewith, namely, cheapness and longevity, are insufficiently appreciated. The disadvantages, surface heterogeneity and irreproducibility, may be overcome by surface modification or coating with small amounts of liquid to reduce heterogeneity and improve reproducibility 4,15). Porous polymers, for example polystyrene and divinyl benzene, are also available. Molecular sieves, discussed in Chapter 17, are used mainly to separate permanent gases. 

Name Gas-liquid (GLC GC) capillary gas (CGC) Stationary phase Solid (absorbent or molecular sieve) Configuration Column Name Gas-solid (GSC)... 

An advantage of cyclodextrins over the common stationary phases is the high selectivity toward the isomeric substances. It has been demonstrated that many positional and geometric isomers can be separated by packed-column GSC in a very short time (i.e. analysis time does not exceed 2 minute) in separation of a mixture of o-, m- and p-isomers. From the analytical viewpoint, the low efficiency of the columns used is a disadvantage. Also, there ar other drawbacks of the gas-solid chromatography using CO s nonlinearity of the separation isotherm over a wider concentration range and poor reproducibility in the preparation of the CD columns utilized. 

As previously mentioned, GC is a two-phase system that consists primarily of a stationary (solid and/or liquid) and mobile (gas) phase. When a liquid stationary phase is used (GLC), the liquid is immobilized as a thin film supported on a finely divided, inert solid support usually consisting of siliceous earth, crushed firebrick, glass beads, or in some cases, the inner wall of a glass tube. In GSC, the stationary phase is an active adsorbent, such as alumina, silica gel, or carbon, which is tightly packed into a tube. 

There are two basic disadvantages to the coated capillary column. First, the limited solute retention that results from the small quantity of stationary phase in the column. Second, if a thick film is coated on the column to compensate for this low retention, the film becomes unstable resulting in rapid column deterioration. Initially, attempts were made to increase the stationary-phase loading by increasing the internal surface area of the column. Attempts were first made to etch the internal column surface, which produced very little increase in surface area and very scant improvement. Attempts were then made to coat the internal surface with di-atomaceous earth, to form a hybrid between a packed column and coated capillary. None of the techniques were particularly successful and the work was suddenly eclipsed by the production of immobilize films firmly attached to the tube walls. This solved both the problem of loading, because thick films could be immobilized on the tube surface, and that of phase stability. As a consequence, porous-layer open-tubular (PLOT) columns are not extensively used. The PLOT column, however, has been found to be an attractive alternative to the packed column for gas-solid chromatography (GSC) and effective methods for depositing adsorbents on the tube surface have been developed. 

Gas chromatography is based on the distribution of a compound between two phases. In gas-solid chromatography (GSC) the phases are gas and solid, the injected compound is carried by the gas through a column filled with solid phase, and pmrtitioning occurs via the sorption-desorption of the compound (probe) as it travels past the solid. Superimposed upon the forward velocity is radial notion of the probe molecules caused by random diffusion through the stationary phase. Separation of two or more components injected simultaneously occurs as a result of differing affinities for the stationary phase. In gas-liquid chromatography (GLC), the stationary phase is a liquid coated onto a solid suppx>rt. The mathematical treatment is equivalent for GLC and CSC. 

Gas-solid chromatography (GSC) and gas-liquid partition chromatography (GLC) are variations of GC. In GSC separations occur primarily by differences in absorption at the solid phase surface. In GLC a nonvolatile liquid is coated or chemically bonded onto particles of column packing or directly onto the wall of a capillary column. Separation occurs primarily by differences in solute partitioning between the gaseous mobile phase and the hquid stationary phase. 

In GSC, separation occurs based on differences in the adsorption of the various components in the sample onto the solid adsorbent. While GSC may not offer as much flexibility in stationary phase functionality as GLC, it has its own advantages. For separation applications, advantages include higher available operating temperatures, higher column efficiencies, and no stationary phase leakage. Typical solid phases for GSC include zeolites, silica gel, activated alumina, carbon, carbon molecular sieves, diatomites, and porous polymers. 

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