Heart-Cut Two-Dimensional Countercurrent Chromatography with a Single Instrument.

Abstract

Countercurrent chromatography (CCC) is a separation technique based on the liquid-liquid partitioning of compounds between the two phases of a biphasic solvent system. Limitations in the separation efficiency and peak capacity of one-dimensional (1D) CCC often result in insufficiently resolved peaks. Therefore, partially resolved peak fractions have to be rechromatographed in order to improve the yield and purity. Additional solvent evaporation steps can be circumvented by the application of two-dimensional CCC (2D CCC). Existing 2D CCC configurations are based on the linking of two CCC instruments which are not readily available in every laboratory. In this study, we introduce a technical improvement which allows performing multiple heart-cuts and 2D CCC separations with one instrument which has up to four independent coils, one pump, and one detector. For this purpose, we modified a commercially available CCC system by the addition of three six-port selection valves and a T-piece. The applicability of the 2D CCC system was shown under overloading conditions with eight alkyl hydroxybenzoates with nonideal conditions. We used two solvent systems which were hydrodynamically compatible and which showed different selectively characteristics with regard to the compounds. Four unresolved compounds in the first dimension were baseline resolved by means of the heart-cut technique, in which between 4 and 9 mL of the flow from coil 1 was transferred to coil 2. Three successive heart-cuts were performed that led to baseline resolution of unresolved compounds in the first dimension. The obtained recovery rates were 94-100%, and the purities of the compounds as determined by GC/MS were 90-100%.