Comparison of three different extraction methods and HPLC determination of the anthraquinones aloe-emodine, emodine, rheine, chrysophanol and physcione in the bark of Rhamnus alpinus L. (Rhamnaceae)

Introduction - Rhamnus alpinus L. (Rhamnaceae), a traditional plants in the flora of the Abruzzo region, is known to contain active anthraquinone secondary metabolites. However, the content of anthraquinones varies among R. alpinus samples depending on collection season and site. Thus, using simple, reliable and accurate analytical methods for the determination of anthraquinones in R. alpinus extracts allows comparative study of different methods of extraction.Objective - After a partial validation of an HPLC method for the simultaneous determination of five anthraquinones, aloe-emodine, rheine, emodine, chrysophanol and physcione, in the bark of R. alpinus, we compared three different methods of extraction.Methodology - Anthraquinones were extracted from the bark of R. alpinus using different techniques (methanol maceration, ultrasonic and supercritical CO₂ extraction). Separation and quantification of anthraquinones were accomplished using a reversed-phase C₁₈ column with the mobile phase of H₂O-methanol (40 : 60, v/v, 1% formic acid) at a wavelength of 254 nm. The qualitative analyses were also achieved at wavelength of 435 nm.Results - All calibration curves were linear over the concentration range tested (10-200 mM) with the determination coefficients ≥0.991. The detection limits (S/N = 3) were 5 mM for each analytes. All five anthraquinones were found in the samples tested at concentrations reported in experimental data.Conclusion - The described HPLC method and optimised extraction procedure are simple, accurate and selective for separation and quantification of anthraquinones in the bark of R. alpinus and allow evaluation of the best extraction procedure between the tested assays. Copyright © 2009 John Wiley & Sons, Ltd.