Closed-loop recycling dual-mode counter-current chromatography. A theoretical study.

Closed-loop recycling dual-mode counter-current chromatography (CLR DM CCC) processes consist of two successive separation stages: separation of solutes in the recycling closed-loop with mobile x-phase and separation of solutes in the counter-current mode with mobile y-phase. Several variants of the implementation of this separation method can be developed: the closed-loop recycling stage may consist of one or several successive separation steps; all components of a mixture can pass through both stages of separation or individual components may be withdrawn from the system at different stages. In this study, such separation processes are theoretically investigated, and simple equations for simulation presented. These equations can help to simulate and select a suitable separation scheme for a given mixture of components. Several examples of separation by CLR DM CCC method are discussed. Examples of simulation are presented in "Mathcad" program. It is shown that CLR DM CCC allows separation of solutes with similar partition coefficients and separation of complex mixtures containing solutes with widely different partition coefficients, providing concentrated fractions of the separated solutes.