THEORY FOR STEP AND PULSE METHOD OF SUPERCRITICAL-FLUID CHROMATOGRAPHY

The paper presents a general retention formula for supercritical. flui d chromatography at finite concentration. A new chromatographic rate t heory based on the fugacities of solutes instead of concentrations isi developed, thus relieving the restrictions of linear isothermal distr ibution and infinite dilution. An expression for retention values of a N component system including solvent is obtained by combining the rat e theory with the mass balance equation of solutes in chromatography. It is shown that there are N-1 characteristic retention peaks for N co mponents and the retention time can be calculated directly from the eq uilibrium properties of the components in both mobile phase and statio nary phase at the given conditions. The theory can be reduced to the w ell known formula for infinite dilution and to the result of step-puls e theory in gas chromatography under low pressure at finite concentrat ion. Supercritical fluid chromatography may eventually prove itself to be a useful reseach tool in the field of phase equilibrium and thermo dynamic properties of supercritical fluid system.