Gas chromatography with wetted soil columns has been used to determine the retention mechanism of pesticides and halogenated methanes (used as soil fumigants). The principal modes of interaction with the wetted soils include adsorption on the water surface and absorption by the water layer. The equilibrium
The differential enthalpies, entropies, and free energies of adsorption for sorbate molecules have been studied in relation to their molar refractions, dipole moments, and specific interactions. The contributions of these molecular parameters to adsorption on columns of Graphon, salt-modified alumina, and saltmodified porous silica beads have been determined. The resulting data allow prediction of retention volumes for other compounds, as well as the molecular conformation of adsorbed polar molecules. The relationship of the thermodynamics of absorption to the types of adsorptive surfaces also is discussed.
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