Other chromatographic modes

The stationary phases used in exclusion chromatography are porous particles with a closely controlled pore size. Unlike other chromatographic modes, in exclusion chromatography there should be no interaction between the solute and the surface of the stationary phase. 

A counter current movement of the mobile phase and the sorbent has some unique advantages when designing separation processes for maximum economy. The efficiency requirement for the sorbent is lower compared to other chromatographic modes, since no individual column has to achieve full resolution. Instead only the pure fractions of the zones obtained are withdrawn from the system. The time-space yield in terms of productivity is enhanced considerably by the improved utilization of the sorbent capacity. The product dilution is lower, pure fractions are withdrawn with high yield and it is not necessary to consider fractions of less then the desired purity. Early on it was re-... 

There are two classes of stationary phases in SEC, one type for GFC and the other for GPC. Stationary phases for GFC are hydrophilic and include polydextrans, polyvinyl alcohol gel, and silica gel those for GPC are hydrophobic, typically cross-linked, rigid polystyrene-divinylbenzene gels. Generally, columns of 15 to 50 cm length are used, packed with 7- to 10-/t,m particles and with an internal diameter between 0.6 and 0.8 cm. In SEC, unlike in other chromatographic modes, the stationary phase is the primary factor controlling retention. 

Affinity chromatography differs from other chromatographic modes in that a suitable stationary phase can specihcally catch either a single or several components out of a random mix of products owing to a naturally occurring biospecitic bond. A suitable elution process then provides the pure compounds (s). 

HPLC fulfills all of these criteria and is now used extensively in the analysis of samples from a variety of sources including mammalian tissue, plant tissue and food extracts. The overall efficiency of HPLC and the variety of chromatographic modes allows the majority of analyses to be performed by either reversed phase, reversed phase ion-pair, normal phase or ion-exchange HPLC. Other chromatographic modes such as size exclusion and affinity have found limited application in the chromatography of the vitamins. 

Affinity chromatography differs from other chromatographic modes in that a suitable stationary phase can specifically catch either a single or several... 

The term MLC is usually given to the use of micellar mobile phases with RPLC columns. A few examples have been described in other chromatographic modes that use similar mobile phases, with normal or reverse microemulsions, bile salts, and surfactants in supercritical fluids. Also, studies using non-RPLC stationary phases and micellar mobile phases have been reported in size exclusion and gel permeation chromatography. These topics are beyond the scope of this article. 

In order to obtain high column efficiency of SEC columns, much Improved packing techniques are required than those used for other chromatographic modes. Thus, SEC columns available to users are all pre-packed. 

Chapter 7 is devoted to important physicochemical —basically mechanistic — aspects of the direct enantioseparations, carried out by using either CSP or mobile phase. In such cases, the diversity of the involved separation mechanisms is much greater than the most of other chromatographic modes (and, particularly, when compared with the relatively simple physicochemical rules governing adsorption or partition liquid chromatography). Thus, the author of this chapter discusses enantioseparation in terms of the solute-chiral selector complexation constants, stoichiometry and selectivity of complexation, the nature of the binding sites on the stationary phase surface, and, finally, the supramolecular mechanisms of complexation. 

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