Frontal chromatography breakthrough curve

TABLE 4 Frontal Chromatography Experimental Breakthrough Curves in Grams Per Liter Obtained for the Mixtures of Mono- and Disaccharides of Different Concentrations... 

The exact shape of a breakthrough curve is mainly determined by the functional form of the underlying equilibrium isotherms of the sample components, but secondary factors such as diffusion and mass-transfer kinetics also have influence. The capacity of the column is an important parameter in frontal chromatography, because it determines when the column is saturated with the sample components and, therefore, is no longer able to adsorb more sample. The mixture then flows through the column with its original composition. 

From a theoretical viewpoint, frontal analysis and displacement chromatography are important and interesting problems because there are as5onptotic solutions for the breakthrough curves of frontal analysis and for the band profiles in the isotachic train in displacement chromatography. An asymptotic solution is an analytical solution obtained after an infinite migration distance. The existence... 

The VERSE method was extended to describe the consequences of protein de-naturation on breakthrough curves in frontal analysis and on elution band profiles in nonlinear isocratic and gradient elution chromatography [45]. Its authors assumed that a unimolecular and irreversible reaction taking place in the adsorbed phase accormts properly for the denaturation and that the rate of adsorption/desorption is relatively small compared with the rates of the mass transfer kinetics and of the reaction. Thus, the assumption of local equilibrium is no longer valid. Consequently, the solid phase concentration must then be related to the adsorption and the desorption rates, via a kinetic equation. A second-order kinetics very similar to the one in Eq. 15.42 is used. 

Frontal analysis A chromatographic process in which a feed solution is abruptly substituted for the mobile phase and pumped through the column. Each component has its own breakthrough curve, but only the least retained one gives a pure zone. This method is used by chemical engineers for bulk purification requirements. In chromatography, it is an acciurate method of isotherm measurement because the retention time of the fronts is related to the amounts adsorbed and is independent of the column efficiency. Also called breakthrough analysis. 

Isotherms can also be obtained by frontal chromatography [171-173]. The MIP is then packed into a column and used as the stationary phase in liquid chromatography. A solution of known concentration of analyte is applied continuously to the column until a breakthrough curve is obtained. After washing the column, the procedure is repeated with increasing concentrations of analyte. The amount analyte bound for each concentration is calculated from the breakthrough curves. 

IGC measurements can be carried out using a pulse or continuous technique. The pulse of probe molecule is introduced into the carrier gas stream. This pulse is transported by the carrier gas through the system to the column with the solid sample. On the stationary phase, adsorption and desorption occur and the result is a peak in the chromatogram. The ratio of adsorption/desorption is governed by the partition coefficient. At fixed conditions of temperature and flow rate, the time of retention of a compound is characteristic of the system. An alternative is the fi ontal technique. This is carried out by injection into the carrier gas stream of a continuous stream of the probe molecule. When the sample enters into the column, there is a distribution between phases, and the concentration profiles takes the shape of a plateau, preceded by a breakthrough curve. The shape of this curve is characteristic of each system [3]. The benefit of the frontal technique is that equilibrium can be always established due to its continuous nature while pulse chromatography requires the assumption of a fast equilibration of the probe molecule adsorption on the surface. Between both techniques, the main part of publications describes pulse experiences, since they are faster, easier to control and more accurate, especially if interactions between probe molecules and the adsorbent are weak. 

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