Short papers in Pharmaceutical Analysis

Abstract

The plant Cutharunthus roseus is an important source of the naturally occurring antineoplastic alkaloids vincristine and vinblastine. The quality control of the extraction process has routinely relied on a two-dimensional thin-layer chromatographic (TLC) densitometric method.' However, the precision obtained by TLC is less than satisfactory. Consequently, an attempt was made to develop a suitable HPLC method.A review of the methods reported in the recent literature revealed that most were unsatisfactory for routine quality control, as they required a complex separatory process or resulted in lengthy retention time~.2-~ However, Gorog er ~1 . ~ proposed an HPLC system, which, although not able to separate completely all of the constituents, was simple, rapid and apparently robust. Preliminary investigations of various packing materials in our laboratories showed that a 10-cm column packed with SAS Hypersil was approximately equivalent to the 25-cm Lichrosorb RP-8 column used in the original method. The optimum eluent composition and the elution order of the different alkaloids were similar for the two columns. It was not possible, however, to separate completely vincristine, ajmalacine and catharanthine from one another using the shorter column, and this observation was consistent with the results from the original 25-cm Lichrosorb RP-8 column reported by Gorog et ul.5In a collaborative study with Professor Goriig and his co-workers, digital methods have been examined to address the problem of deconvoluting overlapping peaks. The present work reports the development of a multi-component suppression system for this purpose that is capable of routine application. The system is based o n a linear photodiode array detector and represents a logical extension of the spectral suppression method originally ExperimentalReagents and Materials A 0.01 M solution of ammonium carbonate (AnalaR grade, BDH Chemicals Ltd., Poole) was prepared with glass distilled water and filtered through a Millipore 0.45 pm filter using an all-glass apparatus. Acetonitrile (HPLC "S" grade, Rathburn Chemicals, Walkerburn) was used as received. The eluent was de-gassed under vacuum in an ultrasonic bath for 15 min. Catharanthine sulphate, vincristine sulphate and ajmalacine were provided by Gedeon Richter Chemical Works (Budapest, Hungary). Standard solutions of each of the analytes alone, in binary and in ternary mixtures were prepared in the HPLC mobile phase. The combination solutions contained vincristine sulphate (84.15 pg ml-l), ajmalacine (89.48 pg ml-1) and catharanthine sulphate (2.14-85.4 pg ml-I ) .