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Characterisation of tannin-containing herbal drugs by HPLC.

INTRODUCTION
Herbal drugs containing tannins are characterised in the European Pharmacopoeia by their tannin content analysed by the old, nonspecific, colorimetric Folin-Ciocalteu method. The result of the analysis is a single figure relating to the content of tannins, but this does not provide much information on the identity or status of the herbal drug.


OBJECTIVE
In the present paper methods for obtaining more detailed information of the constituents in these herbal drugs are described.


METHODOLOGY
The methods developed are based on a reversed-phase gradient HPLC system coupled to DAD, fluorescence, electrochemical and MS detectors.


RESULTS
The HPLC system developed provides characteristic fingerprints of the herbal drugs when using UV detection at 250 nm. The fingerprints may be used for identification of tannin-containing herbal drugs. Methanolysis of the herbal drug generated methyl gallate and ellagic acid, which were analysed in the HPLC system. The molar ratio between methyl gallate and ellagic acid may also be used for the identification of herbal drugs.


CONCLUSIONS
An HPLC system equipped with selective detectors was shown to be valuable in the identification of herbal tannin. Most promising was fingerprinting using UV detection, but methanolysis followed by HPLC also proved useful.