Introduction Rhamni purshianae cortex belongs to the group of herbal drugs containing hydroxyanthracene
glycosides, which are used as laxatives. The pharmacopoeial monographs of such herbal
drugs are currently under revision with regard to the introduction of more specific
and robust assay methods. In this context, also the identification methods are updated
focusing on the anthracene glycosides.
Aims The goal of this work was to optimize the current TLC method for identification C
of the monograph of cascara [1] and to bring it in line with the general monograph 2.8.25 of the European Pharmacopoeia.
Methods Six different samples of cascara were extracted with ethanol 70% v/v and separated
on silica gel 60 HPTLC plates. After derivatisation with hydro-ethanolic potassium
hydroxide solution (50 g/L), the fingerprint was evaluated under UV 366 nm and compared
to that of other anthraquinone containing drugs. Furthermore, suitable substances
were defined as intensity markers and for the SST.
Results A slightly more polar and acidified mobile phase was found to give superior separation
of the four cascarosides A, B, C and D compared to the existing method. Frangulin
A and B were selected as SST-pairs and aloin A and cascaroside A as intensity markers.
Conclusion The fingerprint for cascara was homogenous for six samples and distinctive from the
ones of the compared Frangulae cortex, Aloe capensis, Rhei radix, Sennae angustifoliae
foliolum or fructus samples. A chromatographic table according to the Ph.Eur. has
been elaborated ([Fig. 1]). Therefore, the optimized method is found suitable to replace the existing one
in the monograph of cascara.
Fig. 1 Chromatographic table of the HPTLC fingerprint of Rhamni purshianae cortex, reference
and test solution.
