Estimation of C-glycosides and O-glycosides in cascara (Rhamnus purshiana DC., bark) and cascara extract

Abstract

An assay process is described which enables the cascarosides, the aloins and the O-glycosides of cascara to be estimated separately. The cascarosides are separated from the aloins by partition between water and ethyl acetate; each fraction is then oxidised and hydrolysed by ferric chloride treatment to the free anthraquinones which are determined colorimetrically as aloe-emodin. The O-glycosides are determined colorimetrically as emodin after acid hydrolysis. Results show that commercial extracts contain only about half the theoretical amount of C-glycosides and about quarter of the O-glycosides and there is a significant breakdown of primary glycosides. These results indicate that decomposition occurs during preparation of the official extract. One commercially available extract, which passed current official standards, was shown by the method to be very deficient in activity. In view of the small proportion of O-glycosides in commercial extracts a shortened assay process, for cascarosides and aloins only, is described.