Quantitative determination of physostigmine from aqueous solution

Abstract

A gas chromatographic method is described for the direct determination of physostigmine base from a solution of physostigmine salicylate. The method involves isolation of physostigmine salicylate from an aqueous solution by a freeze drying process, subsequent conversion to a trimethylsilyl (TMS) derivative and gas liquid chromatography. The trimethylsilyl salt dissociates on injection into the flash vapourizer inlet of a gas Chromatograph, and the physostigmine-TMS and salicylic acid-TMS derivatives are eluted separately. Due to the specificity of the silylation reaction it is possible to determine by gas chromatography the alkaloid content in the presence of its degradation products. A modification of the method was necessary for the assay of a commercial formulation containing certain additives.