A NOVEL MERCURIMETRIC TITRATION ASSAY OF METFORMIN HYDROCHLORIDE USING MERCURY (II) THIOCYANATE–IRON (III) NITRATE INDICATOR SYSTEM

Abstract

A simple, rapid, reliable and novel titration procedure for the mercurimetric assay of metformin hydrochloride (MHCl) based on measurement of the chloride content of its hydrochloride salt is described. In this experiment, initially a synthetic mercury(II) thiocyanate [Hg(SCN)2] indicator was prepared by titrating mercury(II) nitrate [Hg(NO3)2] against potassium thiocyanate (KSCN) in the 1:2 stoichiometric ratio using ferric nitrate [Fe(NO3)3]. After addition of a known amount of Hg(NO3)2 to the indicator, the solution was further titrated against the aqueous solution of MHCl until the original red color reappeared. The concentration of chloride present in the volume (of MHCl) utilized for the reaction was found to be reacting in the 2:1 stoichiometric ratio with the Hg(NO3)2 taken in the second titration. The statistical treatment of the experimental data obtained by determining MHCl in the concentration range 0.8281 to 8.281 g/lit, indicates that the procedure is precise and accurate. The procedure was further applied for the analysis of MHCl in tablet formulations. The average recovery and accuracy were found to be in agreement with claimed by the manufacturer. The common excipients used in tablet formulations did not interfere in the determination of MHCl by this procedure as observed by the recovery experiment using standard addition method. The chemistry involved in titration, the action of an indicator at the end point and the factors that affecting the reaction stoichiometry are discussed.
 Keywords: Chloride assay, Mercurimetric titration, Mercury (II) nitrate, Mercury(II) thiocyanate-iron(III) nitrate indicator system, Metformin hydrochloride, Metformin hydrochloride tablets.