Adsorption in gas chromatography with liquid and solid stationary phases

Abstract

The peculiar features and the mechanism of ageing of sorbents containing a non-polar and a polar liquid as the stationary phase coated on a polar support are discussed. Procedures for ageing sorbents in order to improve the reproducibility of retention values have been developed. It is shown that the retention values for a polar sorbate-non-polar stationary phase-polar support system depend substantially on the degree of drying of both the carrier gas (in the chromatographic run) and of the stream of gas used in the ageing treatment. The roles played by the different components of retention have been estimated on the basis of a study of the dependence of the specific retention of n-propanol on the percentage of squalane coated on Celite. Static measurements of adsorption at the liquid-solid support interface have been made for two systems. In addition, for the n-propanol-squalane system static measurements of the partition coefficient have been carried out. The results of static measurements of adsorption at the liquid-solid support interface have confirmed the conclusions on the significant role of adsorption on this surface that have been drawn from the results of chromatographic measurements carried out with sorbents subjected to ageing. The possibilities of using the effects of adsorption at the phase interfaces of sorbents containing liquid and solid stationary phases are considered. A linear dependence of the retention volume or the reciprocal of the percentage of stationary phase is shown to exist when solid stationary phases are used. The height equivalent to a theoretical plate (HETP) is considerably lower when a solid than when a liquid stationary phase is used, owing to a decrease in the resistance to internal diffusion. The HETP decreases sharply if helium is substituted for nitrogen as the carrier gas.