Abstract
The selectivities of TLC systems have been compared by use of correlations between R F(II) and R F(I) values (by analogy with two-dimensional TLC). The greatest spread of spots, indicative of individual selectivity, was obtained for combination of non-aqueous mobile phases comprising a weakly polar diluent (heptane) and a polar modifier (tetrahydrofuran) on silica, and for aqueous mobile phases comprising a polar solvent (methanol) in water on water-wettable octadecyl silica (RP-18W). A good spread of spots was also obtained for pairs of normal-phase systems with hepatane-ethyl acetate mobile phases and reversed-phase systems with water-dioxane mobile phases, both on polar cyanopropyl-bonded layers. The correlation of R F values in normal- and reversed-phase systems were used for practical separation of a mixture of ten urea herbicides by two-dimensional thin-layer chromatography on cyanopropyl-bonded polar adsorbents and by use of a layer comprising two zones — a narrow zone of silica adjacent to a wide ...
Published Version
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