Elution frontal mode

Chromatography (elution or frontal mode), often the final purification step for high purity, is a separation process that depends on partitioning between a flowing fluid (the mobile phase) and a solid adsorbent (the stationary phase). 

Chromatography may be performed as elution, frontal, or displacement. When the mode of development is not specified, a chromatographic separation is considered to be an elution. 

Elute the MIP column in frontal mode with several different concentrations of template in the mobile phase... 

Modes of Operation The classical modes of operation of chromatography as enunciated by Tisehus [Kolloid Z., 105, 101 (1943)] are elution chromatography, frontal analysis, and displacement development. Basic features of these techniques are illustrated in Fig. 

Several theoretical models were constructed to describe the chromatographic process in the frontal 116.191 and the zonal elution mode 20. The conventional method of obtaining the kinetic parameters consists in fitting the model to the experimental breakthrough curves. Another method based on the split-peak effect is a direct measurement of the apparent association rate constant (7,211. Because of the slow adsorption process, a fraction of the solute injected as a pulse into the immunochromatographic column is eluted as a nonretained peak. This behavior is observed at high flow rates, with very short or low-capacity columns 121—251. 

Figure 4 illustrates an example of the HPLC equipment that can be used either for frontal elution mode or for pulse injection analysis. For the pulse injection mode, an injection valve with a small volume sample loop (20 mm ) is placed at... 

The two HPLC pumps and the six-port switching valve permit one to switch from one eluent to the other, and the immunoadsorbent column is automatically regenerated. In addition, for the frontal elution mode, this system permits one to... 

The use of the differential mode of detector operation can be extremely useful in cases where the normal chromatographic development gives very poor separations due to poor distribution kinetics between the two phases. However, the technique does require significantly more sample for frontal analysis than for normal elution development so that sufficient sample must be available. Furthermore, the response of the detector operated in the differential mode is nearly two orders of magnitude less than that when used in the normal mode and so adequate detector sensitivity must be available. 

In the elution mode when the mobile phase contains a competitive additive, in gradient elution when the initial concentration of the strong solvent is different from zero, or in frontal analysis when the elution of successive concentration steps is carried out, the column contains a constant concentration of a component interacting with the stationary phase at the beginning of the experiment. Thus, the initial condition is... 

The term development is used to describe the process by which chemical solutes are transported through the stationary phase. For batch modes of operation, solute development is done by elution or displacement processes. For continuous modes of operation, solute development is accomplished by the process of frontal analysis. 

With this respect exclusion chromatography basically diflers from all other modes of chromatography in that the analytes are not retained by the column packing and, therefore, do not need any special displacer or additional portions of the mobile phase, in order to be eluted from the column. Dilution of fractions separated in accordance with the size exclusion mechanism is no more unavoidable. (Dilution can be minimized to the diffusion effects at the front and tail of the analyte zone.) The absence of any supplementary matter in the frontal exclusion chromatography process relates ISE to the above-defined ideal separation process. 

Apparatus for obtaining thermodynamic data from gas chromatography has been described by a number of authors. Conder and Purnell described a normal pressure apparatus suitable for working at finite concentrations. The apparatus could be operated in three modes, viz. (1) frontal analysis by a characteristic point, (2) frontal analysis, and (3) elution on a plateau. The first method is the most rapid a complete isotherm can be measured and calculated... 

Displacement chromatography is one of the three basic modes of chromatographic operation, the oAict two being frontal analysis and elution chromatography. Displacement chromatography is rarely, if ever, used for analytical separations, but is usefid for preparative separations. It has also been used for trace enrichment... 

In principle, the modes and steps in preparative chromatography do not differ from those in analytical chromatography. Four modes are used (Fig. 4) isocratic elution, linear gradient elution, stepwise elution, and displacement development. Frontal analysis is not used for purification of biomolecules, but it is used for... 

The concept of separating sample components in a column was first developed in 1903 by Mikhail Tswett, who introduced the term chromatography in 1906. Unfortunately, his contemporaries showed little interest for the idea and almost 30 years went by before scientists in Germany rediscovered the principle of column liquid chromatography (LC). Then, in 1943 Arne Tiselius (in Sweden) classified chromatography into three modes frontal, elution, and displacement. The elution mode actually became synonymous with almost all chromatography, but in recent years the displacement mode has attracted new interest, particularly in the separation of proteins. 

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