Polar-bonded stationary phases (CN-silica and Diol-silica) are used with nonaqueous eluents in adsorption mode or with aqueous eluents in partition mode. This enables the application of these systems in two-dimensional separations because of the different selectivity and application to the separation of closely related compounds of similar physicochemical properties and retention behaviour. Similarly, multiphase plates, connected with C18 strips and silica layers, are used with aqueous and nonaqueous eluents. Such layers were applied for the separation of selected coumarins. Thus, differences in separation selectivity are applied for the separation of coumarin fractions from plant extracts of the Apiaceae family by two-dimensional thin-layer chromatography.
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