Qualitative and quantitative evaluation of solvent systems for countercurrent separation

Area of Science:

• Analytical Chemistry
• Separation Science
• Natural Product Chemistry

Background:

• Solvent system selection for countercurrent separation (CS) is crucial but challenging.
• Metabolomic studies require orthogonal CS steps for complex mixtures.
• Developing new CS solvent systems with defined polarity and selectivity is essential.

Purpose of the Study:

• To evaluate solvent system polarity and selectivity for countercurrent separation.
• To introduce a novel method for comparing solvent systems.
• To facilitate the development of solvent systems for orthogonal fractionation protocols.

Main Methods:

• Utilized a 20-component natural product mixture (GUESSmix) to assess solvent systems.
• Measured analyte partition coefficients (K) to define the GUESSmix polarity index (GUPI).
• Employed solvatochromic dyes and electrical permittivity for polarity assessment.
• Calculated pairwise resolution (αip), sweet spot analytes (Nsw), and their resolution (αsw) for selectivity.
• Created 2D reciprocal shifted symmetry plots (ReSS(2)) for visual comparison.

Main Results:

• The GUESSmix effectively characterized solvent system polarity and selectivity.
• GUPI provides a measure of solvent system polarity range.
• Selectivity metrics (αip, Nsw, αsw) enabled intra- and inter-family comparisons.
• ReSS(2) plots visually compared solvent system polarity and selectivity.

Conclusions:

• This study provides a framework for rational solvent system selection in countercurrent separation.
• The developed methods aid in creating suitable solvent systems for successive orthogonal CS protocols.
• Findings support advancements in metabolomic analysis and complex natural product fractionation.