Solid gas chromatography

Availability of solid surfaces which are stable and do not undergo chemical reactions (e.g., oxidation). 

High column efficiencies are possible due to no liquid phase contribution to band spreading. 

Great specificity of surfaces for solute molecule configurations.  

The adaptability of this technique to study the physico-chemical measurements possible at solid surfaces (e.g., isotherms 

Evaluation of catalysts, kinetics of catalytic processes, and catalyst reactions in general. 

GSC is based on adsorption of gaseous substances on solid surfaces. Distribution constants are generally much larger than those for GLC. As a result, GSC is useful for the separation of species that are not retained by gas-liquid columns, such as the components of air, hydrogen sulfide, carbon disulfide, nitrogen oxides, carbon monoxide, carbon dioxide, and the rare gases. 

SC is performed with both packed and open tubular columns. For the latter, a thin layer of the adsorbent is atftxed to the inner walls of the capillary. Such columns are sometimes called porous-layer open tubular. or PLOT, columns. 

Molecular sieves arc aluminum silicate ion exchangers, whose pore size depends on the kind of cation present. Commercial preparations of these materials arc available in particle sizes of 40 to 60 mesh to 00 to 120 mesh. The sieves are classified according to the maximum diameter of molecules that can enter the pores. Commercial molecular sieves come in pore sizes of 4, 5, 10, and 1,1 A, Molecules smaller than Ihese dimensions penetrate into the interior of the panicles where adsorption takes place. For such molecules, the surface area is enormous when compared with the area available to larger molecules. Thus, molecular sieves can be used to separate small molecules from large. For 

27-2 How does a. soap-bubble flow meter work  

27-3 What is meant by temperature programming in GO Why is it frequently used  

GSC is a complementary technique to GLC. Separation is based on the adsorption properties of a solid surface which gives a more active stationary phase and higher retention characteristics than liquid film stationary phases. The distribution ratio, K, and the retention ratio, k, are therefore higher than for GLC columns so that gases and highly volatile compounds which cannot 

Separation of components in GSC is determined by their relative affinity for the adsorbent as described by the distribution ratio, K  

Adsorption results from two properties of the adsorbent, polarity and microporosity. Polarity describes the normal van der Waal s type interactions due to permanent electric effects and may be supplemented by hydrogen bonding. Microporosity describes the presence within the adsorbent macro structure of pores with diameters in the range 50-300 nm (5-30 A). Many active solids are also efficient catalysts and may result in the irreversible adsorption or complete or partial conversion of an analyte giving rise to artefacts which will show up in the chromatogram. There are three main requirements for successful GSC. 

Separation must be carried out at temperatures which are high relative to the boiling point of the analytes, GSC is therefore appropriate for separation of gases and highly volatile substances. 

Adsorbents must have suitable surface characteristics for reversible interaction with the analyte, for example, alumina modified with inorganic salts, silica modified by hydrothermal treatment and silanisation, zeolites, graphitised materials and porous polymers. 

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The most widely used particulate support is diatomaceous earth, which is composed of the silica skeletons of diatoms. These particles are quite porous, with surface areas of 0.5-7.5 m /g, which provides ample contact between the mobile phase and stationary phase. When hydrolyzed, the surface of a diatomaceous earth contains silanol groups (-SiOH), providing active sites that absorb solute molecules in gas-solid chromatography. 

Gas compressibility correction factor (GC) 4 Gas purifier 233, 764 Gas-solid chromatography 199 carbosieves 204 glassy carbon 204 graphitlzed carbon blacks 202 modifiers 204 inorganic oxide adsorbents 200... 

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. 

Gas separation membranes, conducting polymer applications, 7 539 Gas-solid chromatography, adsorption,... 

GLC, gas-liquid chromatography GSC, gas-solid chromatography—no high-boiling liquid, only solid HPLC, high-performance liquid chromatography TLC, thin-layer chromatography. 

Relationships such as Eqs. (45) and (46) have been utilized extensively in correlating solubility properties (such as gas/liquid and liquid/liquid partition coefficients), retention volumes in gas/solid chromatography, capacity factors in high-pressure liquid chromatography, etc.199 200 For instance, gas/liquid partition coefficients for each of 35 different liquid stationary phases were represented with R > 0.985.205 Other applications have been in biochemical and pharmacological areas,199 200 e.g., enzyme inhibition and pollutant effects. 

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. 

Argon is analyzed by mass spectrometry (characteristic ion m/z 40) or by gas-solid chromatography. Its concentration can be increased by several times by selective adsorption over a suitable adsorbent followed by thermal desorption of the gas onto the GC injection port. 

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