Propagation of Signals of Finite Concentration in Gas Chromatography. III. Influence of the Pressure Gradient

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Abstract
Resolution of the equations of the quasi-ideal chromatography model at finite concentration is possible in the case of a finite pressure gradient in the column provided the elution does not change the pressure profile and the pressure variation inside the solute band is neglected. A study of the solution shows that there still exists three models of peak migration, as in the zero pressure gradient case, but that the pressure gradient enhances the isotherm effect. It is not possible, however, to account for the effect of pressure gradient by using an average pressure because there is a convolution between the effect of the pressure gradient and a nonlinear isotherm. Analysis of the double-shock propagation mode and the determination of the limiting transition conditions permit accurate measurement of the curvature of the isotherm at infinite dilution. The experimental results (variation of retention time with peak height for n-pentane in squalane) are in excellent agreement with the predictions of the theoretical model.