Investigation and Optimisation of the Use of Spectrophotometry for the Assay of Simvastatin with in situ Bromine and Three Dyes as Reagents
Keywords:simvastatin, spectrophotometry, bromate-bromide, pharmaceuticals, dyes
Three simple and sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets using bromate-bromide as the bromination reagent in acid medium, and three dyes as subsidiary reagents. All the three methods are based on the bromination of SMT by a known excess of in situ generated bromine followed by determination of unreacted bromine by reacting with a fixed amount of methyl orange (method A), indigo carmine (method B) or meta-cresol purple (method C) and measuring the absorbance at 510, 610 or 540 nm. In all the methods, the amount of bromine reacted corresponds to the amount of SMT. The experimental conditions for the assay have been optimized. In all the methods, the absorbance is found to increase linearly with the concentration of SMT at the respective wavelengths. Beer’s law is obeyed over the ranges 0.5-3.0, 2.5-15.0 and 2.5-15.0 μg mL-1 for method A, method B and method C, respectively and the respective molar absorptivity values are 1.0x105, 2.3x104 and 2.1x104 l mol-1 cm-1. The limits of detection and quantification are reported for all the methods. The performance of the methods was validated according to the present ICH guidelines. The methods gave similar results in terms of precision and accuracy. The repeatability and intermediate precision, expressed by the RSD was better than 2%. The accuracy of the methods expressed as relative error was satisfactory. The proposed methods were applied to the analysis of tablet form of SMT and the results tallied well with the label claim. No interference was observed from the concomitant substances normally added to tablets. The results were statistically compared with those of a literature method by applying the Student’s t-test and F-test. The accuracy and validity of the methods were further ascertained by performing recovery studies via spike method and standard-addition method.
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