PROBLEMS AND APPLICATIONS OF REVERSED-PHASE THIN-LAYER CHROMATOGRAPHY

The various technical problems encountered in the use f chemically bonded silica in thin-layer chromatography (TLC) are discussed. While the use of alkyl grafted silica offers all the advantages of reversed-phase systems for use in TLC, some practical difficulties arise because polar solvents do not completely wet the modified surface. Water-alcohol mixtures with water concentrations above 30% migrate very slowly within the porous layer, resulting in prohibitively long analysis times. Migration over distances exceeding a few centimetres becomes erratic and poorly reproducible. Other problems are encountered with sampling and detection. The plates are very easy to use and permit extremely good separations that were previously very difficult to achieve, especially for polar compounds. Some examples are given. The preparation of samples is especially easy as aqueous solutions need simply be diluted with methanol. © 1979.