The performance of type-I high-speed counter-current chromatography was evaluated by changing the column inclination against the rotating centrifugal force field and the core shape of the coiled column. The separations were performed with two different solvent systems composed of 1-butanol-acetic acid-water (4.75:0.25:5, v/v) (BAW) and hexane-ethyl acetate-methanol-0.1 M HCl (1:1:1:1, v/v) (HEMW) using dipeptides and DNP-amino acid as test samples, respectively. In the first series of experiments, a set of short coiled columns connected in series is mounted around the holder hub in two different ways: in the parallel orientation, all column units are arranged in parallel to each other and mounted on the holder at various angles against the horizontal plane. In the zigzag configuration, the neighboring units of the same column are mounted symmetrically forming various angles apart. In the parallel configuration, for both the BAW and HEMW systems, the retention of stationary phase first increased as the column angle decreased from 90 to 60 and then decreased, as the column angle further decreased from 60 to 0, while Rs (peak resolution) continually declined over the entire column angle range from 90 to 0. But, for both solvent systems, with the zigzag configuration, retention of stationary phase and resolution both decreased as the column angle decreased from 90 to 0. In general, Sf and Rs for separation of dipeptides in the BAW system, from 90 to 15, is better for the parallel orientation than for the zigzag configuration. However, at 0, Sf and Rs are better for the zigzag orientation. In the DNP-amino acid separation with the HEMW system, retention of the stationary phase and Rs for the parallel orientation is better than that for the zigzag orientation from 90 to 30, whereas from 30 to 0 the results are opposite. Over all results of our studies revealed that the formally used column orientation at 90 degree inclination yields the highest peak resolution in both solvent systems. In the second series of experiments,three types of novel coiled column configurations, i.e., a triangular coiled column and two elliptical coiled columns were mounted on the holder of type-I countercurrent chromatograph and their performances were evaluated with the above two solvent systems and test samples. The overall results indicated that the performance of compact type-I counter-current chromatography was improved by elliptical coiled column which was mounted with its maximum coil diameter perpendicular to the surface of the column holder.
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