Effects of the back pressure and the temperature on the finite layer thickness of the adsorbed phase layer in supercritical fluid chromatography

• The excess adsorption isotherms of ethanol on silicagel from liquid CO2 were measured.
• The measurements were made using the method of small disturbances.
• These measurements were made for a range of pressures and temperatures.
• Analysis of the excess isotherm provides estimate of the layer thickness of the adsorbed phase.
• Increasing temperature and decreasing pressure results in a thicker adsorbed layer.

The excess adsorption isotherm of ethanol from liquid carbon dioxide on a silicagel column was determined in a range of back pressures and temperatures. The retention patterns of minor disturbance peaks were mapped and their dependences on the applied back pressure and column temperature measured. The analysis of the linear decreasing part of the excess isotherm around its inflection point provided the finite layer thickness of the adsorbed phase. Our results show that increasing the temperature and decreasing the back pressure result in a thicker layer of the layer of enriched organic solvent above the silicagel surface.