Alkalimetric titrations of salts of organic bases in the Pharmacopoeia

Česká verzia

Authors: Želmíra Bezáková; Mária Stankovičová
Authors place of work: Bratislava, Slovenská republika ; Katedra farmaceutickej chémie FaF UK
Published in the journal: Čes. slov. Farm., 2013; 62, 264-269
Category: Original Articles

Summary

Modified methods – alkalimetry in ethanol 70% with a defined small volume of hydrochloric acid 0.01 mol/l added to the solution of the sample before the titration and alkalimetry in ethanol 70% or ethanol 96% alone with potentiometric end-point detection for the assay of halide salts of 11 organic N-bases has been investigated. The results were compared to those obtained by the method of the European Pharmacopoeia 7th Ed. (Ph. Eur. 7th Ed.). The Ph. Eur. 7th Ed. use for 8 investigated substances alkalimetry in alcohol 96 % with a defined small volume of hydrochloric acid 0.01 mol/l (5 ml) with potentiometric end-point detection: Cinchocaine hydrochloride, Codeine hydrochloride dihydrate, Ethylmorphine hydrochloride, Lidocaine hydrochloride, Papaverine hydrochloride, Pilocarpine hydrochloride, Quinine hydrochloride, Tetracaine hydrochloride. Our results revealed that the Ph. Eur. 7th Ed. method did not work for 5 drugs from this group: Cinchocaine hydrochloride, Ethylmorphine hydrochloride, Papaverine hydrochloride, Pilocarpine hydrochloride and Tetracaine hydrochloride. In the group of investigated substances we included also drugs with the character of weak organic bases for which Ph. Eur. 7th Ed. prescribed different methods for their assay: Thiamine hydrochloride and Pyridoxine hydrochloride – acidimetric titration in non-aqueous solvents with perchloric acid and Procaine hydrochloride – determination of primary aromatic amino-nitrogen (Ph. Eur. 7th Ed., chapter 2.5.8).

Keywords:
weak organic bases • alkalimetry • potentiometric end-point detection • assay

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