Improvement of separation in zonal preparative thin-layer chromatography by gradient elution

Summary Complex extracts of the plants Azulan and Hemorigen were separated by zonal micropreparative thin-layer chromatography in sandwich chambers of the ES and DS type which permitted zonal application of large volumes of sample, without auxiliary equipment. Application from the edge of the layer, in the frontal chromatography mode, markedly improved the separation efficiency and capacity owing to displacement effects which narrow the initially broad zones. Further improvement of separation efficiency and purity of fractions, revealed by densitometry, was observed using stepwise gradient elution. This was confirmed by extraction of some of the separated fractions from the layer and rechromatography; the composition of these fractions were generally simpler than for the corresponding isocratic chromatograms.