Mixed retention mechanisms in gas-liquid chromatography : II. Contributions of adsorption and partition to the retention volume in systems with polar solutes and non-polar stationary phase on a silanized support

Abstract

The contributions from adsorption and partition at infinite and finite solute concentrations have been investigated for a gas-liquid chromatography system with a silanized support, non-polar stationary phase (octadecane) and polar solutes (ethyl methyl ketone and diisopropyl ether). It was found that the contribution from adsorption varied strongly with the sample size. The variation of adsorption with liquid loading at infinite solute concentration showed a rapid decrease between 0 and 1% loading followed by a rapid increase at ca. 5%. To explain this behaviour it is suggested that one part of the stationary phase is blocking the most active sites (dominating at very low liquid loading) and another part is forming droplets on the surface of the support. The variation of adsorption with liquid loading for loadings higher than ca. 2% can be explained by the variation of the gas-liquid interfacial area with liquid loading. It is therefore concluded that the dominant adsorption mechanism for loadings higher than ca. 2% is the adsorption at the gas-liquid interface.