HPTLC identity testing for Rhamni purshianae cortex

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.

Publication History

Article published online:
13 June 2022

• References

• 1 EDQM. European Pharmacopoeia, 10th edition (2020): Cascara, Monograph 0105