A Comparative Study of the Hydrolytic and Non-Hydrolytic Methods for The Assay of Solanaceous Drugs

Abstract

The results given by the hydrolytic and non-hydrolytic methods of determining the total alkaloidal content are in good agreement for belladonna, hyoscyamus and stramonium ; the agreement is fair for Duboisia leichhardtii and Datura sanguinea, whilst for Duboisia myoporoides the non-hydrolytic method gives high values. An improved paper chromatographic system for the separation of the principal tropane alkaloids has been developed ; the system was used to determine the individual alkaloidal content of the respective drugs and to provide the appropriate factor for converting titre to percentage of total alkaloid.A POTENTIAL source of error in the conventional assay of solanaceous drugs occurs in the final stage of the determination, in which the extract of the total alkaloids is directly titrated against standard acid after removal of the volatile bases by heating at 100". Errors may arise from incomplete removal of volatile bases, the presence of non-volatile nonalkaloidal bases (for example, tropine and oscine), or the retention of traces of ammonia by the alkaloidal extract1-'.To obviate these possible sources of error Reimers proposed a modified method in which the alkaloidal extract is hydrolysed and the liberated carboxylic acids are extracted and titrated against standard alkalis~9.This method was subsequently incorporated in the International Pharmacopoeia as one of two alternative procedures for the assay of solanaceous vegetable drugs. Except for Hyoscyamus muticusg and stramoniumlO, however, there is no literature on the results given by the two techniques, and accordingly a comparative study of the direct and hydrolytic methods was undertaken with drugs from commercial sources. PRELIMINARY EXPERIMENTS Loss on Heating of Alkaloids and Amino Alcohols at 100"In the official assay it is specified that the extract of the bases be heated at 100" and weighed at intervals of 1 hour until two successive weighings do not differ by more than 1 mg. In view of the long periods of heating required by some extracts to reach constant weight, account had to be taken of the effect of prolonged heating of tropane bases at 100". Information is given in the literature only for atropine and hyoscyamine, and is conflicting. Thus Hardyll and DeKay and Jordad2 stated that atropine is non-volatile at 100"; on the other hand, Schousen13 and Fricke and Kaufmad4 reported that prolonged heating of atropine and hyoscyamine at this temperature results in loss by decomposition or volatilisation.Aliquots of standard solutions of the pure bases in chloroform were evaporated to dryness; the residues were heated at 100" for 0, 1, 2 and 241 T Q