High-Pressure Gas Chromatography and Chromatography with Supercritical Fluids. I. The Effect of Pressure on Partition Coefficients in Gas-Liquid Chromatography with Carbon Dioxide as a Carrier Gas

Abstract

Gas-chromatographic experiments with CO₂ as a carrier gas, conducted at temperatures of 30 to 40°C and pressures up to 80 atm, showed a pronounced drop of the partition coefficient with increasing pressure. This effect, which can be interpreted as a raise in solute volatility, is proved to be mainly due to nonideality in the gas phase. The gain in volatility (by a factor of 10 or more) permits gas-chromatographic separations to be carried out at lower temperatures than usual. As partition coefficients were found to drop very fast near the critical point of the carrier gas, operation at pressures well above this point may open up the possibility of handling compounds too heavy for ordinary gas-chromatographic practice. Interesting possibilities of class separation can be deduced from the study of the pressure effect in homologous series. Some potential non-analytical applications of high-pressure gas chromatography are discussed.