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 (lgKM/L) 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 (lgKU/M) between the upper and middle phases of the small polarity compounds increases with increasing logP values. LogP vs lgKM/L 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 lgKM/L 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.

Comprehensive separation of a wide variety of compounds from olive leaves by counter-current chromatography with three-phase solvent system.

The three-phase solvent system counter-current chromatography has been of great research interest, because it can separate compounds with a wide range of polarity. The solvent system of n-hexane/methyl tert-butyl ether/acetonitrile/water (5:5:7:5, v/v) was used for counter-current chromatographic comprehensive separation of olive leaves. The study adopted the normal elution mode. The middle phase and the lower phase (at a volume ratio of 7:3) were pumped into the column simultaneously, followed by eluting with the upper, middle, and lower phases in sequence. The retention rate of the stationary phase measured by the experiment was 73.5%. The upper phase was used to elute the nonpolar compounds, then the mobile phase was switched to the middle phase to elute the moderately hydrophobic compounds, finally, the polar compounds were eluted by the lower phase remaining in the chromatographic column. This method successfully separated eight compounds in one step within 270 min and five compounds were identified. The logP values of these five compounds were 7.44, 7.86, 4.16, -0.11, and 0.96, respectively, covering a wide range of polarities. The present study demonstrated that the three-phase solvent has a strong extraction capacity for ingredients from extremely hydrophilic compounds to extremely hydrophobic compounds.

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.