Ionic polymerisation as a means of end-point indication in non-aqueous thermometric titrimetry. Part III. The determination of alkaloids and alkaloidal salts

Abstract

Strychnine, nicotine, atropine, quinine, papaverine, caffeine and theophylline have been determined in amounts down to 0·0001 mequiv, e.g., 33 µg of strychnine and 8·5 µg of nicotine, by catalytic thermometric titration. The hydrochlorides of quinine and ephedrine, ephedrine sulphate, codeine phosphate and atropine methonitrate have been determined by direct titration by using the same technique. Addition of mercury(II) acetate was not necessary in the titration of the hydrochlorides.

Titrations were carried out in non-aqueous solution with 0·1, 0·01 and 0·001 M perchloric acid, with the ionic polymerisation of α-methylstyrene to indicate the end-point. Depending on sample size and the procedure adopted, each determination can be carried out in 2 to 5 minutes by using a manual method, with a thermometer for temperature measurement, or a simple automatic apparatus.

The method would appear to be suitable for the determination of alkaloids and related basic compounds that have been extracted from crude drugs, formulations or natural materials with non-basic organic solvents. For most of the determinations it is not necessary to dry wet chloroform extracts before titration.