In-Silico UHPLC Method Optimization for Aglycones in the Herbal Laxatives Aloe barbadensis Mill., Cassia angustifolia Vahl Pods, Rhamnus frangula L. Bark, Rhamnus purshianus DC. Bark, and Rheum palmatum L. Roots

For the European Pharmacopoeia (Ph. Eur.) herbal monograph draft of Cassia angustifolia Vahl. and Cassia senna L. leaves and pods, a safety limitation of aloe-emodin and rhein was proposed, due to toxicological concerns. A quantitative, analytical method of the anthraquinone aglycones in all Ph. Eur. monographed herbal laxatives is of interest. A rational method development for the aglycones aloe-emodin, rhein, emodin, chrysophanol, and physcion in five herbal drugs was realized by using 3D chromatographic modelling (temperature, solvent, and gradient time) and design of experiment (DOE) software (DryLab® 4). A methodical approach suitable for the challenging peak tracking in the chromatograms of the herbal drugs in dependence on the changes in the chromatographic conditions is described by using a combination of mass spectroscopy (MS) data (UHPLC-QDa), UV/Vis-spectra, and peak areas. The model results indicate a low robust range and showed that with the selected chromatographic system, small interferences could not be averted. The separation achieved shows a pure UV/Vis spectrum for all aglycones except for chrysophanol in Aloe barbadensis and emodin in Cassia angustifolia fruit. A gradient with the best resolution of the aglycones in all five drugs is proposed, and its suitability demonstrated for the quantification of aglycones in these herbal drugs.