Reversed-flow gas chromatography applied to physico-chemical measurements

Abstract

Physico-chemical measurements by reversed-flow gas chromatography can be performed by creating a diffusion current of the gaseous solute into the carrier gas, perpendicular to the chromatographic movement, and superimposing on it the effect of a rate or equilibrium process taking place at one end of the diffusion column. The reversals of the direction of the carrier gas flow give rise to a series of sample peaks which, plotted as the logarithm of their height vs. time, form a so-called diffusion band. From a non-distorted diffusion band, the void fraction (porosity) of a solid bed, and the partition coefficient of a solute between a gas phase and a solid phase can be determined. From a distorted diffusion band, mass transfer and partition coefficients across gas—solid and gas—liquid boundaries are computed, and also reaction rate constants when the solute transferred to the solid reacts chemically with it. Furthermore, mass transfer coefficients, connected with the evaporation of pure liquids and liquid mixtures, and also activity coefficients of one or more components in these mixtures, can be determined.