Elution Procedure

In both hydrostatic and hydrodynamic CCC, separation is initiated by filling the entire column with the stationary phase of a mutually equilibrated two-phase solvent system. This is followed by injection of the sample solution through the sample port. Then, the mobile phase is eluted through the column in the correct elution mode while the apparatus is rotated at a suitable speed (except for DCCC). Although sample injection may be made after the column had been equilibrated with the mobile phase (the routine procedure in HPLC), this practice does not usually improve the separation in CCC.

In hydrostatic CCC systems, the direction of elut-ing the mobile phase should be chosen in such a way that the upper phase is eluted against the acting force field (ascending mode), and the lower phase along the force field (descending mode). In hydrodynamic CCC systems, the direction of the Archimedean screw force also plays an important role in the retention of the stationary phase. Generally speaking, the lower phase should be eluted from the head toward the tail, and vice versa for the upper phase. For various polymer phase systems (such as polyethylene glycol/dextran) with a high viscosity, maximum retention of the stationary phase is usually obtained by using the less viscous phase as the mobile phase.

As in HPLC, CCC permits the use of gradient or stepwise elution. The method requires suitable selection of the solvent system so that the volume of the stationary phase in the column is not significantly altered by the mobile phase. Some examples are n-butanol/water with a concentration gradient of dichloroacetic acid or trifluoroacetic acid, and polymer phase systems with a pH gradient of sodium or potassium phosphate.

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Solar Panel Basics

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