NOVEL DESIGN FOR CENTRIFUGAL COUNTERCURRENT CHROMATOGRAPHY: IV. FIGURE-8 COLUMN

Novel design for centrifugal counter-current chromatography: VI. Ellipsoid column

A novel ellipsoid column was designed for centrifugal counter-current chromatography. Performance of the ellipsoid column with a capacity of 3.4 mL was examined with three different solvent systems composed of 1-butanol-acetic acid-water (4:1:5, v/v) (BAW), hexane-ethyl acetate-methanol-0.1 M HCl (1:1:1:1, v/v) (HEMH), and 12.5% (w/w) PEG1000 and 12.5% (w/w) dibasic potassium phosphate in water (PEG-DPP) each with suitable test samples. In dipeptide separation with BAW system, both stationary phase retention (Sf) and peak resolution (Rs) of the ellipsoid column were much higher at 0° column angle (column axis parallel to the centrifugal force) than at 90° column angle (column axis perpendicular to the centrifugal force), where elution with the lower phase at a low flow rate produced the best separation yielding Rs at 2.02 with 27.8% Sf at a flow rate of 0.07 ml/min. In the DNP-amino acid separation with HEMW system, the best results were obtained at a flow rate of 0.05 ml/min with 31.6% Sf yielding high Rs values at 2.16 between DNP-DL-glu and DNP-β-ala peaks and 1.81 between DNP-β-ala and DNP-L-ala peaks. In protein separation with PEG-DPP system, lysozyme and myolobin were resolved at Rs of 1.08 at a flow rate of 0.03 ml/min with 38.9% Sf. Most of those Rs values exceed those obtained from the figure-8 column under similar experimental conditions previously reported.

Advances in countercurrent chromatography for protein separations

Countercurrent chromatography (CCC) is a preparative purification technique working with biphasic liquid systems. One phase of the liquid system is selected to be the mobile phase, the other phase is the stationary phase, held still by centrifugal fields. Aqueous two-phase systems (ATPS) have demonstrated their use in biological purifications. This article reviews protein separations done by CCC using ATPS. The two types of CCC ‘columns’ – hydrostatic and hydrodynamic instruments – are presented. All commercially available CCC equipments are listed. The hydrostatic CCC columns have an interesting potential to purify proteins working with ATPS aqueous liquid phases. The ATPS properties are briefly summarized, giving the polyethylene glycol 1000/dipotassium phosphate/water ternary mass phase diagram, along with the full chemical compositions of the two aqueous phases of important mixtures of this ATPS. Most published protein purifications were performed in academic laboratories. The highest throughput listed is 1.65 g/h of pure lyzozyme, obtained using a 5.5 l hydrostatic CCC column.

Evaluation of the performance of protein separation in figure-8 centrifugal counter-current chromatography

The performance of protein separation using the figure-8 column configuration in centrifugal counter-current chromatography was investigated under various flow rates and revolution speeds. The separation was performed with a two-phase solvent system composed of polyethylene glycol 1000/potassium phosphate each at 12.5% (w/w) in water and with lysozyme and myoglobin as test samples. In order to improve tracing of the elution curve, a hollow fiber membrane dialyzer was inserted at the inlet of the UV detector. The results showed that the retention of stationary phase (Sf) and resolution (Rs) increased with decreased flow rate and increased revolution speed. The highest Rs of approximately 1 was obtained at a flow rate of 0.01 mL/min under a revolution speed of 1200 rpm with a 3.4 mL capacity column.

Evaluation on the performance of four different column models mounted on the compact type-I coil planet centrifuge

Optimal positions of coiled separation columns on the type-I centrifuge were determined for four typical two-phase solvent systems to obtain the best separation efficiency (resolution and retention of stationary phase) for each with a suitable set of test samples. A set of short coiled columns is connected in series and mounted around the holder hub in four different ways: (model A) the tail of one unit with left-handedness was connected to the head of the next unit with right-handedness (TL-HR); (model B) the tail of one unit with left-handedness was connected to the tail of the next unit with right-handedness (TL-TR); (model C) the tail of one unit with left-handedness was connected to the tail of the next unit with left-handedness (TL-TL); (model D) the tail of one unit with left-handedness was connected to the head of the next unit with left-handedness (TL-HL). The results indicated that the performance of model D was the best among the four models. High revolution speed (800 rpm) is favorable to separation using the moderately hydrophobic solvent system of hexane-ethyl acetate-methanol-0.1M HCl (1:1:1:1, v/v) (HEMW), while lower revolution speed (600 rpm) is beneficial to the separation with polar solvent system of 1-butanol-acetic acid-water (19:1:20, v/v) (BAW).

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.

Novel Designs for Centrifugal Countercurrent chromatography: V. Comparative Studies on Performance of Various Column Configurations

The conventional toroidal coil in centrifugal countercurrent chromatography has a low level of stationary phase retention, since a half of each helical turn is entirely occupied by the mobile phase. In order to cope with this problem, several new column designs including zigzag, saw-tooth and figure-8 patterns have been introduced and their performance was compared in terms of retention of the stationary phase (Sf), peak resolution (Rs), theoretical plate number (N) and column pressures. Overall results of experiments indicate that the figure-8 column yields the highest Rs when the lower phase is used as the mobile phase. Since the column pressure of all these new columns are much lower than that in the traditional toroidal coil column, the separation efficiency can be improved using a long separation column without a risk of column damage by high back pressure.