Role of three-phase solvent system in the counter-current chromatography.

In counter-current chromatography, the separation efficiency greatly depends on the partitioning ability of the separated substance between the stationary phase and the mobile phase. Partitioning ability is mainly represented by the parameter partition coefficient which is one of the important parameters to evaluate the separation effect of counter-current chromatography. The scope of the partition coefficient value mainly depends on the solvent system. A suitable solvent system election is, therefore, a critical role in the separation of counter-current chromatography. The existing solvent systems that are widely used are mainly two-phase solvent systems. It is difficult to decide on an appropriate solvent system for the separation of compounds with a wide polarity range, which promotes the development of the three-phase solvent system in counter-current chromatography. This review mainly described the origin, development history of three-phase solvent system, summarized the volume ratios and volume fractions of the upper, middle, and lower phases of nearly 50 three-phase solvent systems, their advantages, and disadvantages in counter-current chromatography. In addition, the challenges and future perspectives on three-phase solvent systems in counter-current chromatography also are discussed in this review.