82 first a temperature suitable for the separation of

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82 First, a temperature suitable for the separation of the first eluting component is selected, and then the temperature is increased so that the second component is separated and so on. The change in temperature can be linear, parabolic, step, or any other formula. The chromatographic separation where the temperature is changed during the elution process is called TPGC. A separation like the one below can be obtained:
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83
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84 Temperature Zones in GC Three temperature zones should be adjusted before a GC separation can be done. The injector temperature should be such that fast evaporation of all sample components is achieved. The temperature of the injector is always more than that of the column, which depends on the operational mode of the separation. The detector temperature should be kept at some level so as to prevent any solute condensation in the vicinity of the detector body.
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85 Gas-solid chromatography (GSC ) Gas-solid chromatography is based upon adsorption of gaseous substances on solid surfaces. Distribution coefficients are generally much larger than those for gas- liquid chromatography. Consequently, gas- solid chromatography 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, and rare gases. Gas-solid chromatography is performed with both packed and open tubular columns.
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86 Molecular Sieves Molecular sieves are metal aluminum silicate ion exchangers, whose pore size depends upon the kind of cation present, like sodium in sodium aluminum silicate molecular sieves. 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 13 angstroms. Molecular sieves can be used to separate small molecules from large ones.
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87 Porous Polymers Porous polymer beads of uniform size are manufactured from styrene crosslinked with divinylbenzene. The pore size of these beads is uniform and is controlled by the amount of crosslinking. Porous polymers have found considerable use in the separation of gaseous species such as hydrogen sulfide, oxides of nitrogen, water, carbon dioxide, methanol, etc.
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88 Quantitative Analysis GC is an excellent quantitative technique where peak height or area is proportional to analyte concentration. Thus the GC can be calibrated with several standards and a calibration curve is obtained, then the concentration of the unknown analyte can be determined using the peak area or height. The detector response factor for each analyte should be considered for accurate quantitative analysis.
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89 Gas chromatographs are widely used as criteria for establishing the purity of organic compounds. Contaminants, if present, are revealed by the appearance of additional peaks. Qualitative Analysis is usually done by comparison with retention times of standards, which are very reproducible in GC, provided good injection practices are followed. Injection should be done with a
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