Displacement development

The second classification scheme is less common than the first but is found in the literature. It is based on the operating method, or the mechanism by which the sample is removed from the column, and is therefore dependent on the nature of the mobile phase. This classification, which was introduced by Tiselius21 in 1940, includes elution development, displacement development, and frontal analysis, as shown in Figure 1.2.22 In practice, only elution and to a lesser extent displacement development are commonly used. 

A schematic for developing displacement separations is shown in Fig. 12. The first step consists of selecting a stationary phase and mobile phase conditions which result in the greatest selectivity for the separation problem at hand. The SMA parameters of the principal components of the mixture should then be determined as described earlier. 

Experimental work of Kalasz et al. resulted in the statement of the characteristics and basic rules of displacement chromatography. They conceived properties of the fully developed displacement train, factors affecting displacement development, efficacy of separation, analysis of displaced fractions, determination of displacement diagrams from Langmuirian isotherms, as well as selection of the column, carrier, and displacer for displacement chromatography. Concentration of the sample is a particular feature of displacement chromatography. However, the displacer in the carrier is also definitely concentrated through the development of the displacement train. 

Isotachic migration of the component zones in the fully developed displacement train. 

The adjacent zones of a totally developed displacement train touch each other, even in the optimal separation. 

After having reached the state of a fully developed displacement train, aU bands move with the same velocity, which is the velocity of the displacer front. 

Displacement development. Displacement development consists of elution or development of the separation procedure by a solvent which has a greater affinity for the stationary phase than the sample components. The sample mixture is first introduced on to the end of the column and adheres to the SP. Elution occurs when a displacing solvent is passed through the column progressively displacing the components from the SP. The components separate due to their varying distribution ratios, K, and partition or adsorption properties, that is, their relative attraction for the SP with respect to the MP. Components with the least affinity for the stationary phase will be displaced first. 

Kalasz et al. showed that even a very short distance (e.g., 2 cm in the case of 5% displacer) may be sufficient for the formation of a fully developed displacement train. HPDC is devoted to preparative scale separation. Fractions result in HPDC the fractions are collected and analyzed off-line. The appropriate fractions can be combined to yield the pure compounds. D-TLC was grown into an approach for scouting the optimum conditions for HPDC. Its goals are to find the proper carrier, the proper displacer, and the appropriate displacer concentration in the carrier. A series of experiments proved that the results of D-TLC can be transferred to HPDC. ... 

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