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APPLICATION OF CPC AND RELATED METHODS FOR THE ISOLATION OF NATURAL SUBSTANCES

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APPLICATION OF CPC AND RELATED METHODS FOR THE ISOLATION OF NATURAL SUBSTANCES ( application-cpc-and-related-methods-forisolation-natural-sub )

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224 BARTOSZK DZIERSKIetal. Retention of the substance should not be too high ñ not to let the substance remain too long on the column, nor too low for it not to be washed out immediately. For this reason, it is important to select a solvent suitable to maintain the partition coeffi- cient and hence the corresponding retention (6). Solvents are chosen also on the basis of other parameters, that is the difference in density between the two liquid phases, on the viscosity of the liquid, or on the interfacial tension. To determine the appro- priate solvents, thin layer chromatography (TLC) method is often used. It may be done by developing the sample on a silica plate with solvents. The sol- vents that give retention factor in the range Rf = 0.4ñ0.6 are best suited for CPC analysis (7). The column is a place where substances are separated. Centrifugal force is necessary to keep the stationary phase on place, while the mobile phase flows through. Thus, the stationary phase is stable only when the device rotor sets the column in motion, and is creates centrifugal forces (6). In addition to the appropriate solvents selec- tion, it is also important to set the right flow rate and speed of rotation of the rotor in the CPC apparatus. The impact of these factors on the distribution of the substance was conducted by Matsuda et al. (8). It appeared that low rotation of the rotor and high flow rate can result in insufficient retention. The results also showed that the flow rate reduction improves peak resolution and increased the number of theo- retical plates. It was concluded that the higher flow rate increased the minimum value of the rotor speed, which allowed for adequate resolution (8). CPC apparatus There are two types of liquid-liquid chro- matography columns: hydrostatic and hydrodynam- ic ones. On the primary column of the first type (hydrostatic), the mobile phase passed through the stationary phase only by gravity (DCCC ñ Droplet Counter Current Chromatography), however, it requires long elution time (1). Modern hydrostatic counter-current known as CPC (centrifugal partition chromatography) enables to speed up the process. CPC unlike DCCC produces a centrifugal force of the rotor, which allows faster movement of the mobile phase through the stationary phase. This gives a wider range of solvents that can be used in this method (7). CPC displaced DCCC method because it is much more efficient (9). The most widely used techniques are two slightly different types of CPC apparatus. One is produced inter alia by Pharma-Tech Research Corp., and the second by Sanki Engineering Ltd. (2). The second in its original form had a column separator in the form of rolls arranged around the rotor connect- ed by narrow tubes. Column is filled with the sta- tionary phase through which the mobile phase is passed as a stream thanks to the rotation of the rotor (5). The other components of the device were: sol- vent pump, valve regulating the flow, the dispenser of the sample, a detector and a recording device (2). Diagram of such a device is presented in Figure 1. Advantages of CPC CPC as the analytical technique is much more advantageous than other types of chromatography fractions tank Figure 1. Diagram of CPC device

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