Using the liquid nature of the stationary phase: The elution-extrusion method

Countercurrent chromatography (CCC) is a chromatographic technique with a support-free liquid stationary phase. Taking advantage of the liquid nature of the stationary phase, it is possible to perform unique operations not possible with chromatographic methods based on solid stationary phases. The principle of band broadening inside a chromatographic column is extensively detailed using the random walk model in a hypothetical 200 cell Craig machine. It should be noted that the zone spreading inside the column depends only on the band position, not on the time or number of transfers that were needed to carry the band at its position. Since the whole column content is liquid in CCC, it is possible to extrude it after the bands are separated without waiting for the elution in the mobile phase. It was found that the extrusion step did not disrupt the separated bands too much, provided that the centrifugal field was not modified. The elution-extrusion protocol is given. A mixture of steroid compounds is used to validate the method. An application of the method in the rapid estimation of the hydrophobicity range of microbial extracts in an industrial laboratory is presented.