Validated and Sensitive Spectrophotometric Methods for Estimation of Rizatriptan Benzoate in Pharmaceutical Formulations using Cerium (IV) Sulphate

Three simple, sensitive and accurate spectrophotometric methods have been developed for the determination of rizatriptan benzoate (RZT) in pure form and pharmaceutical formulations. The proposed methods are based on the oxidation of rizatriptan benzoate by a known excess of cerium(IV) sulphate in acid medium followed by determination of unreacted cerium(IV) sulphate by adding a fixed amount of amaranth (AM), methylene blue (MB), and indigo carmine (IC) dyes followed by measuring the absorbance at 518, 663 and 609 nm, respectively. The experimental conditions affecting the reaction were studied and optimized. The beer’s law was obeyed in the concentration ranges of 1.0-10, 0.5-8.0 and 1.0-14 μg mL^-1 using AM, MB and IC methods, respectively with a correlation coefficient ≥ 0.9993. The calculated molar absorptivity values are 1.0505 × 10⁴, 1.7331 × 10⁴ and 1.3508 × 10⁴ L mol^-1 cm^-1 using AM, MB and IC methods, respectively. The limits of detection and quantification are also reported. Intra-day and inter-day precision and accuracy of the methods have been evaluated. The methods were successfully applied to the assay of rizatriptan benzoate in tablets and the results were statistically compared with those of the reference method by applying Student’s t-test and F-test. No interference was observed from the common tablet excipients. The accuracy and reliability of the methods were further ascertained by performing recovery studies using the standard addition method.