Extraction and Planar Chromatographic Separation Techniques in the

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In microchemical detection methods the TLC plate is sprayed with or dipped into a suitable
reagent to form absorbing or fluorescent derivatives with the analytes which can then be
detected. Derivatization can take place either before or after the TLC separation, and the
terms pre- and postchromatographic derivatization are used to separate these two options. A
great number of different universal and specific, i.e. group-characterizing reagents which
react with a specific functional group, have been developed and new variants continue to be
published (e.g. STAHL 1967, JORK et al. 1990, 1994, TOUCHSTONE 1992).
Biological detection of separated substances on the TLC plate in situ has been applied to the
screening of various extracts for e.g. antimicrobial and antioxidant activity or general toxicity
(EBERZ et al. 1996, WEINS and JORK 1996, HOSTETTMANN et al. 1997). These methods
are especially suitable for screening purposes as the fractions or compounds with most
pronounced activity can be detected directly on the TLC plate and subjected to further
purification and/or identification steps.