Extra-column volume in CCC

Countercurrent chromatography (CCC) is used by natural products and medicinal chemists for fractionation of extracts of flora and fauna to screen for pharmacological activity, and in isolating and purifying gram quantities of individual natural and synthetic compounds. The large extra-column volume in CCC apparatus, particularly in the coil-planet centrifuge designs employing an anti-twisting flow line assembly, may lead to errors in the calculation of the distribution ratios of eluting fractions. The effect of extra-column volume is to delay the time required for a peak to reach the detector. This delay is equal to the transit time of the extra-column volume plus half of the mobile-phase portion of the sample volume. The effect is negligible for columns of large volume (300 mL) but becomes more significant for small columns (15 mL) and for large sample volumes. Manual correction for the effect is very tedious, but results obtained using a generally applicable spreadsheet are presented and discussed. A second spreadsheet is also indicated wherein peak retention times, along with sample and extra-column volume, are entered for calculation of distribution constants, which are summarized on a single page convenient for entry in a notebook.