Liquid-solid chromatography mobile phase selection

In adsorption chromatography the mobile phase is usually a liquid and the stationary phase is a finely-divided solid adsorbent (liquid-solid chromatography). Separation here depends on the selective adsorption of the components of a mixture on the surface of the solid. Separations based on gas-solid chromatographic processes are of limited application to organic mixtures. The use of ion-exchange resins as the solid phase constitutes a special example of liquid-solid chromatography in which electrostatic forces augment the relatively weak adsorption forces. 

L. R. Snyder, J. L. Glajch, and J. J. Kirkland, Theoretical basis for systematic optimization of mobile phase selectivity in liquid-solid chromatography solvent-solute localization effects, /. Chromatogr. 218 (1981), 299-326. 

Figure 6.13. Separation mode selection guide for TLC. LSC = liquid-solid chromatography on an inorganic oxide adsorbent BPC = liquid-solid chromatography on a chemically-bonded sorbent RPC = reversed-phase chromatography with a water-containing mobile phase and chemically-bonded stationary phase IPC = ion-pair chromatography with reversed-phase separation conditions and PC = precipitation chromatography. (From ref. [151] Elsevier)...

Immobilization. The ability of cyclodextrins to form inclusion complexes selectively with a wide variety of guest molecules or ions is well known (1,2) (see Inclusion COMPOUNDS). Cyclodextrins immobilized on appropriate supports are used in high performance liquid chromatography (hplc) to separate optical isomers. Immobilization of cyclodextrin on a solid support offers several advantages over use as a mobile-phase modifier. For example, as a mobile-phase additive, p-cyclodextrin has a relatively low solubility. The cost of y- or a-cyclodextrin is high. Furthermore, when employed in thin-layer chromatography (dc) and hplc, cyclodextrin mobile phases usually produce relatively poor efficiencies. 

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