The Ideal Model in Gas Chromatography

Band Profiles of Single-Components with the Ideal Model 

If the isotherm is supposed to be linear, the equilibrium isotherm does not intervene in the band profile and the global effect is derived from the flow properties. The characteristic method applies. It shows that, in linear gas-chromatography, although the isotherm is linear, the sorption effect causes the velocity associated with a given concentration to decrease with increasing concentration. [22]. A slice of mobile phase having a given mole fraction, X, moves with the velocity 

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The equilibrium-dispersive model had been discussed and studied in the literature long before the formulation of the ideal model. Bohart and Adams [2] derived the equation of the model as early as 1920, but it does not seem that they attempted any calculations based on this model. Wicke [3,4] derived the mass balance equation of the model in 1939 and discussed its application to gas chromatography on activated charcoal. In this chapter, we describe the equilibrium-dispersive model, its historical development, the inherent assumptions, the input parameters required, the methods used for the calculation of solutions, and their characteristic features. In addition, some approximate analytical solutions of the equilibrium-dispersive model are presented. 

The model of ideal linear gas chromatography (Equation 1) [12] also describes the transport of a chemical species in the temperature gradient of a vacuum tube. At molecular flow conditions the linear velocity of the carrier gas, which is identical to the transport velocity of the adsorbate in the gas phase, has to be substituted by the fraction of the column length over the average retention time of the species in the column ... 

In order to ensure the contimiity and clarity of the presentation some frequently-used concepts of chromatography ivith a mobile gas phase are briefly considered the mechanism of separation the retention parameters and the theories of gas chromatography. The employment of this technique as an important method of studying solutions through the most representor-live statistical models is also discussed it has hec7i of use in testing the non-ideal behaviour of some systems. 

In order to give an idea of the usefulness of gas-liquid chromatography in checking the main theories of solutions and to establish its performance in the quantitative treatment of molecular interactions in solutions through deviations from ideality, some thermodynamic data which are particularly useful in the determination of activity coefficients will be considered schematically. At the same time, models of solutions applied in the deduction of activity coefficients will be presented. The expressions of these quantities will be considered for the case of infinite dilution, according to the requirements of chromatographic conditions. In practice the limita-... 

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