METHODS AND MANIPULATION 55 allow the mixture to separate, and use the upper (organic) layer. Under the above conditions, but using this solvent, the spots are decisively but not so widely separated, for the R F values for the anthranilic and the methylanthranilic acid are now 0-68 and 0-81 respectively. ION EXCHANGE The principle of ion exchange is employed in the separation of organic com-pounds on a semi-micro scale or micro scale. Broadly speaking, the use of ion exchange materials* is, in some respect, similar to the use of adsorbents in ordinary chromatography. Ion exchange materials are usually described as (a) cation exchange resins and (6) anion exchange resins. Ion exchange materials are usually resins with acidic or basic groups incor-porated into their molecular structures. Such resins are commercially available and are usually made by the co-polymerisation of styrene and divinylbenzene. The latter forms cross linkages between chains of polymerised styrene to give
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