Dual-mode high-speed counter-current chromatography: retention, resolution and examples

Counter-current chromatography (CCC) is a very versatile technique offering high resolution power in recovering very pure compounds from complex matrices. Dual-mode CCC where the phase role is reversed during the separation is investigated here; it ensures elution of all the injected species from the column while, unlike backflush, the separation is still progressing after phase reversal; equations giving retention and retention factor are derived from the basic equations of chromatography. Compared to normal-mode CCC, it is shown that enhanced resolution in dual-mode CCC can be obtained in conditions derived from a theoretical model. The experimental section provides the validation of the retention prediction while resolution is also proven to be enhanced in dual-mode CCC. However, equations given in the theoretical section cannot fully explain the results obtained for resolution because they do not deal with kinetics. Dual-mode CCC has also been applied to separation of polyoxypropylene glycol polymers; separation can be achieved with a small number of experiments because all the injected compounds are eluted by reversing the phases. Dual-mode CCC also gave improved yields in the purification of antibiotics compared with previous results using normal-mode CCC.