Universal Chromatography

D. Ishii, Kumamoto Institute of Technology, Kumamoto, Japan T. Takeuchi, Gifu University, Gifu, Japan

Copyright © 2000 Academic Press

Chromatography is classified into gas chromatography (GC), supercritical fluid chromatography (SFC) and liquid chromatography (LC), depending on the physical properties of the mobile phase. Since the mobile phase in GC is a gas such as helium or nitrogen that does not have any interaction with analytes and carries them through the column, it is called a carrier gas. On the other hand, the mobile phase in LC dissolves analytes and will interact with them. Therefore, the mobile phase in LC significantly affects the selectivity of the separation. Although there are many options to improve the selectivity of the separation in LC, experience and knowledge are required for optimization. In SFC a high density gas is employed as the mobile phase, where the temperature and pressure in the column are higher than the critical values of the mobile phase employed. The mobile phase in SFC has intermediate properties between those in GC and in LC. Table 1 compares physical properties of the mobile phase in three chromato-graphic modes. The density, viscosity and diffusion coefficients determine the solubility of analytes, permeability of the column and the speed of analysis, respectively.

The effect of temperature on retention behaviour in SFC on a thermodynamic basis has been discussed elsewhere, as well as thermodynamic retention behaviour in open tubular capillary SFC. It was found that LC-like or GC-like retention mechanisms were involved in the supercritical temperature region, depending on the column temperature and the inlet pressure.

Generally, separations in GC are performed using completely different systems from those in LC. The separation system in SFC is a hybrid between GC and LC. However, it should be noted that the temperature and pressure can control the physical properties of the mobile phase. If these two parameters are controlled, separations can be obtained in any three chromatographic modes using a single chromatographic system. Both plunger and syringe pumps can be used for this purpose.

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