Principles of chromatographic separation procedures

True ion exchange is the most usual process in which one type of ions, attracted by electrostatic forces to functional groups of the ion exchanger, is interchanged by another type of ion with the same charge. Ion exchange is mostly combined with elution chromatography. Details of these processes are discussed in section 4.5.2.I. 

Ion exclusion is the chromatographic separation of non-electrolytes (which do not interact with functional groups and penetrate the ion exchangers freely) or ions of weak electrolytes (which enter the grains of ion exchangers of the same charge 

Ion retardation is a process opposite in its result to ion exclusion. It is effected on special amphoteric snake-cage resins (cf., section 4.5.2.1). These ion exchangers will bind electrolytes but not non-electrolytes. One of the first typical examples described by Hatch et al. [146] is the chromatographic separation of glycerol (which leaves the column first) from sodium chloride using Retardion 11A8. The salt retained can be washed from the column by elution with water only. 

2 in a novel form of binding the boric acid was not present as a component in the buffer but it was covalently attached to the exchanger. Monosaccharides were chromatographed through a column containing iV, A[-diethyl-7V-(/ -methylphenyl-boryl) aminoethyl-Sephadex and anionic complexes formed were indicated by their relative retention volumes. 

Bioaffinity elution (also known as substrate or biospecific elution) was described by Pogell [155], and later by Haar [156], and has recently been reviewed by Scopes 

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