The separation regularity of the three-phase solvent system of counter-current chromatography based on polarity parameter modeling.

The three-phase solvent system of counter-current chromatography can separate compounds with a wide range of polarity, but there is no study of its separation regularity. Therefore, in this work, the separation regularity of the three-phase solvent system was initially investigated from the perspective of solvent polarities and compound polarities. The standard compounds covering a wide polarity range were selected, and three-phase solvent systems, n-hexane/methyl acetate/acetonitrile/water, and n-hexane/methyl tert-butyl ether/acetonitrile/water were used for modeling. The results showed that in the three-phase solvent system, the partition coefficient for the middle and lower phases (lgK) increased with increasing logP values in three intervals logP < 0, 0 < logP < 4, and logP > 4. In addition, the partition coefficient for the upper and middle phases (lgK) between the upper and middle phases of the small polarity compounds increases with increasing logP values. LogP vs lgK of 7 solvent systems were employed for the smoothing spline fit through a predictive model design of the curve fitting toolbox in MATLAB software, and good results were achieved. LogP versus lgK for n-hexane/methyl tert-butyl ether/acetonitrile/water solvent systems were used for the second-order power fit, and satisfactory results were obtained. The relationship between polarity parameters and separation case parameters was explored using a heat map approach. The separation regularity of the three-phase solvent system was preliminarily investigated. This regularity study gives hope of assistance to the chemists studying three-phase solvents and counter-current chromatography.