Analysis and stability of the constituents of Curcuma longa and Harpagophytum procumbens tinctures by HPLC-DAD and HPLC-ESI-MS

In continuation of our studies on the constituents and stability of herbal drug preparations [1,2], the present work reports the qualitative and quantitative profiles of the constituents of tinctures of Curcuma longa ground rhizomes and Harpagophytum procumbens radices and their chemical stability. The tinctures were prepared according to the European Pharmacopoeia XI [3]. The ratio between the dry plant material and the final tincture was 1:5. Batches (about 10ml) of each tincture were subjected to accelerated thermostability testing at 40°C. during a 6-month period. Two methods based on liquid chromatography with diode array detection (HPLC/DAD) coupled to an electrospray ionization (ESI) interface were developed for the determination of constituents in both the tinctures. The constituents were identified by UV and MS spectral data and further confirmed by comparison with reference data or authentic samples. Isolations and NMR analyzes were carried out in order to confirm the presence of artifacts where necessary. Constituents responsible for the pharmacological activity (iridoids expressed as harpagoside, verbascoside and curcuminoids) were considered for the quantitative analysis. The developed assays were simple and effective and permitted the quality control of both tinctures. The methods were validated for linearity, limits of detection and quantification, precision, including time precision, and accuracy. All validation criteria were fulfilled. Concerning the stability studies, results showed that H. procumbens tincture remained stable under the conditions applied, whereas curcuminoids in C. longa tincture were reduced to 30% of their initial amount in the accelerated thermostability test.

References: 1. Bilia, AR et al. (2001) Chromatographia 53: 210–15.

2. Bilia, AR et al. (2007)J. Pharm. Biom. Anal. 44: 70–78.

3. Eudra/Q/92/021: ‘Note for Guidance on stability testing of new active substances and medicinal products’.