„PRISMA”: Ein Modell zur Optimierung der mobilen Phase für die Dünnschichtchromatographie, vorgestellt anhand verschiedener Naturstofftrennungen1

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Abstract
In the present paper the TLC application of the “PRISMA” model - which was recently developed for mobile phase optimization in normal and reversed-phase HPLC - is described. The performance of the optimization design is demonstrated with the separation of mixtures of naturally occurring compounds in the low and medium polar range (anthraquinone aglycones, dihydroxanthyletin esters, furocoumarins, secoiridoid glycosides, bipyridyl isomers and esters of salicin). The prism described by “PRISMA” consists of an unlimited number of triangular solvent diagrams (horizontal functions) where every triangular plane corresponds to a different solvent strength (vertical function). Generally the mobile phase consists of four solvents, although it is possible to have mobile phases consisting of three or two solvents. Firstly, ten solvents of the eight selectivity groups of Snyder are selected and tested as mobile phases, either pure or if required diluted with n-hexane. The three best solvents resulting from these experiments are chosen to determine the corners of the prism. The solvent strength of the mixture is then adjusted by diluting with n-hexane. In the next step, at the optimum solvent strength, the selectivity is optimized by choosing three points near the corners of the triangle. If further optimization is required, other appropriate solvent combinations are tested. The “PRISMA” model offers a wide range of solvent combinations and leads in systematic steps to optimized mobile phases. „Die Kunst des Chromatographierens besteht nach wie vor darin, die stationäre Phase auf die mobile Phase und beide auf die Trenntechnik abzustimmen.” (E. Stahl)

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