A water-free solvent system containing an L-menthol-based deep eutectic solvent for centrifugal partition chromatography applications.

Centrifugal partition chromatography (CPC) is a well-established technology for natural compound separation. However, the separation of hydrophobic compounds is still challenging since the number of non-aqueous biphasic systems that can be used in CPC is limited. In this work, we evaluate quaternary solvent systems composed of n-heptane, methanol, and a eutectic solvent composed of L-menthol and levulinic acid, containing DES-constituents in both phases. It was evaluated whether the phases of the systems can be used as stationary and mobile phases for CPC separations. For this purpose, solutes that cover a broad range of octanol-water partition coefficients, i.e. hydrophobic to hydrophilic compounds, were used and shake flask experiments were performed to determine solute partition coefficients. The partition coefficients indicated that the more hydrophobic compounds were in the favored range for CPC and, thus, the systems are high potential candidates for the separation of hydrophobic compounds. In this particular solute set, the biphasic systems were most suitable for compounds with octanol-water partition coefficients between 2.1 and 12.0. It was shown that the biphasic systems with low initial DES-content are stable in presence of water, while L-menthol precipitates from the biphasic systems with high initial DES content when water is added. High stationary phase retention of up to 79.1% could be obtained and the selected model compounds were separated with high resolution in pulse injections, which confirmed the high potential of the biphasic solvent systems for CPC.