Since different compounds will travel a different distance in the stationary phase, chromatography can in effect be used as an isolation technique. The separated compounds each occupying a specific area on the plate, they can be scraped away, put in another solvent to separate them from the stationary phase and used for further analysis. As an example, in the chromatography of an extract of green leaves (for example spinach ) in 7 stages of development, Carotene elutes quickly and is only visible until step 2. Chlorophyll A and B are halfway in the final step and lutein the first compound staining yellow. Once the chromatography is over, the carotene can be removed from the plate, put back into a solvent and ran into a spectrophotometer to characterize its wavelength absorption.
This second edition of Plant Drug Analysis includes nearly 200 new color photographs of superb quality demonstrating chromatograms of all relevant standard drugs. The atlas will be a useful reference for analyzing plant drugs, identifying unknown drugs or monitoring the purity or constituents of a given drug.
All drugs presented meet the standard of the official pharmacopoeia and originate from well defined botanical sources. With this guide one can easily use the technique of thin layer chromatography without previous pharmacognostic training. Only commercially available equipment and reagents are needed, the sources as well as all practical details are given.