Studies on the effect of column angle in figure-8 centrifugal counter-current chromatography.

The performance of the figure-8 column configuration in centrifugal counter-current chromatography was investigated by changing the angle between the column axis (a line through the central post and the peripheral post on which the figure-8 coil is wound) and the centrifugal force. The first series of experiments was performed using a polar two-phase solvent system composed of 1-butanol-acetic acid-water (4:1:5, v/v) to separate two dipeptide samples, Trp-Tyr and Val-Tyr, at a flow rate of 0.05 ml/min at 1000 rpm. When the column angle was changed from 0° (column axis parallel to the centrifugal force) to 45° and 45° to 90° (column axis perpendicular to the centrifugal force), peak resolution (Rs) changed from 1.93 (Sf=37.8%) to 1.54 (Sf=30.6%), then to 1.31 (Sf=40.5%) with the lower mobile phase and from 1.21 (Sf=38.8%) to 1.10 (Sf=34.4%), then to 0.99 (Sf=42.2%) with the upper mobile phase, respectively, where the stationary phase retention, Sf, is given in parentheses. The second series of experiments was similarly performed with a more hydrophobic two-phase solvent system composed of hexane-ethyl acetate-methanol-0.1M hydrochloric acid (1:1:1:1, v/v) to separate three DNP-amino acids, DNP-glu, DNP-β-ala and DNP-ala, at a flow rate of 0.05 ml/min at 1000 rpm. When the column angle was altered from 0° to 45° and 45° to 90°, Rs changed from 1.77 (1st peak/2nd peak) and 1.52 (2nd peak/3rd peak) (Sf=27.3%) to 1.24 and 1.02 (Sf=35.4%), then to 1.69 and 1.49 (Sf=42.1%) with the lower mobile phase, and from 1.73 and 0.84 (SF=41.2%) to 1.44 and 0.73 (Sf=45.6%), then to 1.21 and 0.63 (Sf=55.6%) with the upper mobile phase, respectively. The performance of figure-8 column at 0° and 90° was also compared at different flow rates. The results show that Rs was increased with decreased flow rate yielding the highest value at the 0° column angle with lower mobile phase. The overall results of our studies indicated that a 0° column angle for the figure-8 column enhances the mixing of two phases in the column to improve peak resolution while decreasing the stationary phase retention by interrupting the laminar flow of the mobile phase. Published by Elsevier B.V.