Separation selectivity has been optimized in two-dimensional thin-layer chromatography (2D TLC) by connecting diol or silica plates (on which NP chromatograms were developed) to RP-18W plates (on which reversed-phase chromatograms were developed). Retention of test substances was investigated to select optimum chromatographic systems for separation of selected phenolic compounds by 2D TLC. Selection of optimal mobile phases was performed on the basis of plots of retention against mobile phase composition. The next step of the optimization was calculation of statistical data for correlation of
values for pairs of chromatographic systems — NP diol-RP C
or silica-RP C
. Orthogonal chromatographic systems were selected on the basis of these correlations and used to separate phenolic compounds present in plant extracts. For example, extracts from
were separated by use of optimum 2D TLC systems.