Determination of ranitidine hydrochloride in pharmaceutical preparations by titrimetry and visible spectrophotometry using bromate and acid dyes

Abstract

Four new methods using titrimetry and spectrophotometry are described for the determination of ranitidine hydrochloride (RNH) with potassium bromate as the oxidimetric reagent and acid dyes, methyl orange, indigo carmine and metanil yellow. In direct titrimetry (method A), the drug is titrated directly with bromate in acid medium and in the presence of excess of bromide using methyl orange indicator. In back titrimetry (method B), the drug is treated with a measured excess of bromate in the presence of bromide and acid, and the unreacted bromine is determined iodometrically. Both spectrophotometric methods are based on the oxidation of RNH by a known excess of bromate in acid medium and in the presence of excess of bromide followed by estimation of surplus oxidant by reacting with either indigo carmine (method C) or metanil yellow (method D), and measuring the absorbance at 610 or 530 nm. In methods B, C and D, reacted oxidant corresponds to the drug content. The experimental conditions are optimized. Titrimetric procedures are applicable over the ranges 1–10 mg (A) and 1–17 mg (B), and the reaction stoichiometry is found to be 1:1 (BrO – 3: RNH). In spectrophotometric methods, the absorbance is found to increase linearly with increasing concentration of RNH, which is corroborated by the calculated correlation coefficient ( r) of 0.9984 (C) and 0.9976 (D). The systems obey Beer’s law for 2–12 and 1–7 μg ml –1, for methods C and D, respectively. Method D with a molar absorptivity of 9.82 × 10 4 l mol –l cm –1 is found to be more sensitive than method C ( ε = 2.06 × l0 4 l mol –1 cm –1). The limits of detection and quantification are reported for both the spectrophotometric methods. The proposed methods were applied successfully to the determination of RNH in tablets and injections. The reliability of the assay was established by parallel determination by the official method and by recovery studies.