Liquid phase sorption, competitive

Despite the fact that both normal and monomethyl-substituted paraffins readily enter the pores of ZSM-5 and ZSM-11, preferential sorption of the normal isomer is observed under thermodynamic equilibrium, non-kinetically controlled conditions. Whereas small-pore zeolites, such as 5A and erionite, totally exclude branched hydrocarbons, and large-pore zeolites exhibit little preference, the intermediate pore-size zeolites ZSM-5 and ZSM-11 show a marked preference for sorption of the linear paraffin, even under equilibrium conditions. Competitive liquid phase sorption studies at room temperature indicated selectivity factors greater than ten in favor of n-hexane relative to... 

Stationary phase considerations. The retention mechanism(s) by which bonded phases retain solutes is complex and not fully understood [71-73]. It may be that it is comparable in behaviour and function to conventional partitioning in liquid-liquid phase systems or there may be competition between eluant and solute molecules for position on the stationary phase. It is likely that there are several mechanisms operating however it is adequate to regard the stationary phase as a conventional, physically retained liquid with which analytes interact by the conventional sorption processes. 

A distinctive feature of adsorption from solution is that the surface is always completely covered and the sorption mechanism involves competition between the components of the liquid phase. Detailed theoretical interpretation of isotherms from liquid mixtures is most often based on binary liquid systems. The isotherms are measured by immersing the solid sample into the liquid phase. The concentration is monitored by UV, refractive index (RI), or other analytical methods. 

Surface phase capacity, i.e., the total amount of substances in the adsorbed phase is the second factor determining the sorption properties of the solid sorbents. This quantity is useful for calculating thermodynamic functions which characterize competitive adsorption at the liquid - solid interface and for determining the specific surface area of the sorbents. 

This involves partitioning of molecules between the surface of a solid stationary phase and a liquid mobile phase. The d5mamic equilibrium of solutes as they switch between the stationary and mobile phases (the processes of sorption and desorption, respectively) is specific for each molecule and is affected by competition that exists between solutes and solvent for sites on the stationary phase. This is a purely physical process involving the formation of no... 

A number of experimental techniques have been described for the determination of isotherms based on frontal analysis, frontal analysis by characteristic point, elution by characteristic point, and perturbation methods [12,21,27,169,176-179]. Most authors report single-component isotherm results. Multiple-component isotherm data are more complicated because all components are simultaneously in competition for the sorption sites on the stationary phase. The retention time and peak shapes of any solute is dependent on the concentration and properties of all other solutes in the mixture [12,170,180]. For multicomponent mobile phases in liquid and supercritical fluid chromatography this includes each component of the mobile phase. 

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