Modeling of two semi-continuous methods in liquid-liquid chromatography: Comparing conventional and closed-loop recycling modes.

Two high throughput steady-state methods of counter-current chromatography separations: conventional (SS CCC) and closed-loop recycling (SS CLR CCC) are proposed, evaluated and compared. The methods are based on the application of semi-continuous sample loading technique: the CCC setup includes two mobile phase tanks - one with the pure mobile phase and the second - with the sample solution in the mobile phase. The mobile phase pump is periodically switching from one tank to another. The sample solution is continuously loaded into the CCC column over a constant time with the constant volumetric rate equal to the flow rate of the pure mobile phase. Analytical expressions are developed to describe the SS CCC and SS CLR CCC separations with semi-continuous sample loading. Examples of separation of binary and multicomponent mixtures are discussed. The SS CLR CCC has been shown to provide a multiple increase in the performance and effectiveness of CCC devices. Several examples of simulation of SS CLR CCC separation with semi-continuous sample loading are presented in "Mathcad" program. For the experimental verification of the theory, the separation of the binary mixture caffeine/ coumarin was studied. The biphasic solvent system hexane/isopropanol/water (1:1:1), was used. The comparison of experimental and simulated separations demonstrated a reasonable agreement between theory and experiment.