Quantitative determination of physostigmine in solution

Abstract

A chemical assay is described for the indirect determination of physostigmine (eserine) in solution. The method involves a chemical reaction between methylamine, a hydrolysis product of physostigmine, and carbon disulphide to form a dithiocarbamic acid which is subsequently titrated with a standard aqueous sodium hydroxide solution. The alkaline hydrolysis of the physostigmine sample is carried out at room temperature using a closed system. The difference in the amount of methylamine found in a physostigmine hydrochloride solution before hydrolysis (blank) and after hydrolysis (sample) is indicative of the amount of intact alkaloid present. This indirect determination of methylamine makes it possible for the first time, to determine conveniently the amount of the alkaloid in solution in the presence of its degradation products.