Development of solvent systems with room temperature ionic liquids for the countercurrent chromatographic separation of very nonpolar lipid compounds

- Four IL were evaluated for use in CCC separation of very nonpolar lipid compounds.
- Search started with solubility studies of IL with fourteen organic solvents.
- IL were then added to two organic solvents in which they were miscible/immiscible.
- 24 monophasic mixtures of two organic solvents became biphasic by adding IL.
- n-heptane/chloroform/[C10mim][OTf] provided a partial CCC separation of PPP and CS.

Solvent systems are not readily available for the separation of very nonpolar compounds by countercurrent chromatography (CCC). In this study we therefore evaluated the suitability of room temperature ionic liquids (IL) in organic solvents for the CCC separation of the extremely nonpolar lipid compounds tripalmitin (PPP) and cholesteryl stearate (CS). The four IL tested were [C10mim][OTf], [C2mim][NTf2], [P66614][NTf2], and [P66614][Cl]. Search for a CCC-suited solvent system started with solubility studies with fourteen organic solvents. Following this, combinations were made with one organic solvent miscible and one organic solvent immiscible with IL (147 combinations). Twenty-four initially monophasic mixtures of two organic solvents became biphasic by adding IL. Several unexpected results could be observed. For instance, n-hexane and n-heptane became biphasic with [P66614][Cl]. Further nine systems became biphasic although the IL was not miscible in any of the two components. These 33 solvent systems were investigated with regard to phase ratio, settling time, share of IL in the upper phase and last not least the KU/L values of PPP and CS, which were 8.1 and 7.7 respectively. The most promising system, n-heptane/chloroform/[C10mim][OTf] (3:3:1, v/v/v) allowed a partial separation of PPP and CS by CCC which was not achieved beforehand.