Chromatography sorption effect

The usual inverse gas chromatography, in which the stationary phase is the main object of investigation, is a classical elution method that neglects the mass transfer phenomena it does not take into account the sorption effect and it is also influenced by the carrier gas flow. In contrast to the integration method, the new methodology... 

If the isotherm is supposed to be linear, the equilibrium isotherm does not intervene in the band profile and the global effect is derived from the flow properties. The characteristic method applies. It shows that, in linear gas-chromatography, although the isotherm is linear, the sorption effect causes the velocity associated with a given concentration to decrease with increasing concentration. [22]. A slice of mobile phase having a given mole fraction, X, moves with the velocity... 

Jacob et al. used the method of characteristics to discuss the general properties of the system of mass balance equations in multicomponent preparative gas chromatography (GC) [34-36], assuming either a linear or a nonlinear isotherm. The GC problem is more complicated than the HPLC one because the gas mobile phase is much more compressible than a solution and the mobile phase velocity is very different inside and outside a high concentration band because the partial molar volumes of compounds are much larger in the gas mobile phase than in the condensed stationary phase (the sorption effect). They showed that the method of characteristics appHes to multicomponent systems as well as to single component... 

Sorption Effect A nonlinear effect due to the difference in the partial molar volumes of the component in solution in the mobile phase, and adsorbed on the stationary phase. In liquid chromatography this effect is negligible. It is important in gas chromatography. 

Cooperative effects are of considerable interest for high capacity chromatography of BAS, since for practical purposes high-selectivity bonding is possible only in cooperative processes. This is very important for carrying out the sorption, separation and concentration of BAS. 

Solvents, UV cut-olf values, 70 Solvents, miscibility, 75 Solvophobic effect, 201,203 Solvophobic inleHlclidHk, IS2, 20i Solvophobic ion chromatography, 242 Solvophobic theory, 141,148,152,155, 158, 202, 203, 226, 228, 246 8omatostedn, 263,290 Sorbents, polymeric, 127 Sorption isottom, 159 Soiption kineties, efbet on column effi-cieney in RPC, 227 Speed of aepantion, optimization [Pg.172]

H. Irth, R. Tocklu, K. Welten, G. J. de Jong, R. W. Frei and U. A. Th Brinkman, Trace enrichment on a metal-loaded thiol stationary phase in liquid chromatography effect of analyte structure and pH value on the (de)sorption behaviour , J. Pharm. Biomed. Anal. 7 1679-1690(1989). 

Figure 13.2. Illustration of molecular separation according to their size in a size-exclusion chromatography (SEC) column. The underlying principle of SEC is that particles of different size will elute through a stationary phase at different rates Larger molecules will take less time (or elution volume) to reach outlet of the column as compared to the smaller ones.The prerequisite of a direct correlation between elution time and molecular size is an absence of interactions between the stationary phase and an analyte. Otherwise, nonexclusion effects such as electrostatic repulsion or sorption must be considered.

In the previous chapters we have examined the two factors that must be considered to understand how separations occur. One is the kinetic factor that describes how analyte molecules spread into an increasingly wide zone during their transport through the chromatographic bed. The other is the thermodynamic factor that explains the interactions between analyte and the chromatographic phases resulting in differential sorption or retention in the bed. In this chapter we will combine these two factors and see how a separation is effected. For simplicity, the discussion will be limited to column chromatography. 

In a series of studies we recently demonstrated (29, 30, 63-67) that the resolution of peptides on reversed phase can be profoundly influenced by the addition of appropriate counterionic reagents to a mobile phase of deflned pH, ionic strength, and water content. Retention under these conditions can be discussed in terms of ion-air associations between the ionized peptide and a counterion in the mobile phase and subsequent sorption of the complex onto the stationary phase. Alternatively, adsorption of the counterion, particularly if it is lipophilic, onto the nonpolar stationary phase may occur, and peptide retention would then be mediated by dynamic liquid-liquid ion-exchange effects. Arguments in favor of the participation of one, the other, or both of these alternative pairing-ion phenomena in ion-pair chromatography have been extensively reviewed (16, 28b, 62, 68, 68a). It can be shown (62, 68) that retention behavior in ion-pair systems can be described by... 

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