Estimation of Adsorption Layer Capacity by Sandwich Thin-Layer Chromatography

Abstract

The use of sandwich tanks with a capillary solvent delivery system permits the determination of the volume of the developing solvent in the adsorbent layer as well as the position of the solvent demixing front. Therefore, the adsorption isotherms of polar solvents from solutions in nonpolar diluents and the adsorption layer capacities can be determined in a simple manner, analogous to the column technique: Instead of determination of breakthrough volume, the solvent demixing front on the thin layer is localized by means of a series of test dyes whose spots flatten and merge on the steep solvent composition gradient. The method is illustrated for nine aliphatic ketones adsorbed from heptane and benzene solutions. The experimental results indicate different modes of adsorption from solutions in the two diluents; the surface areas corresponding to one solute molecule are also different for symmetrical dialkyl ketones and isomeric methyl-alkyl ketones.