Effect of the drug-matrix on the stability of enalapril maleate in tablet formulations (original) (raw)
International Journal of Pharmacy and Pharmaceutical Sciences, 2015
Objective: Simple, sensitive, precise, reproducible and validated visible spectrophotometric methods have been developed for the determination of an angiotensin converting enzyme inhibitor (ACE) drug, namely enalapril maleate (ENP) in pure and pharmaceutical dosage forms. Methods: The methods are based on the formation of yellow colored ion-pair complexes between enalapril with two sulphonphthalein acid dyes, bromocresol purple (BCP) and bromophenol blue (BPB) at pH 2.8 and 3.0 using BCP and BPB, respectively followed by their extraction with chloroform. Several parameters such as pH, buffer type, reagent volume, sequence of addition and effect of extracting solvent were optimized to achieve high sensitivity, stability, low blank reading and reproducible results. Results: The absorbance is measured at 408 and 414 nm using BCP and BPB reagents, respectively. The stoichiometric ratio of the formed ion-pair complexes was found to be 1:1 (drug: reagent) for both methods as deduced by Job's method of continuous variation. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9993-0.9996) were found between the absorbance's and the concentrations of enalapril over the concentration ranges of 2.0-24 μg ml-1 and 2.0-28 μg ml-1 with limits of detection (LOD) of 0.39 and 0.45 μg ml-1 , using BCP and BPB methods, respectively. Various analytical parameters have been evaluated and the results have been validated by statistical data. Conclusion: The proposed methods were validated in accordance with ICH guidelines and successfully applied to the determination of enalapril in pure and Dosage forms. Statistical comparison of the results obtained by applying the proposed methods with those of the official method revealed good agreement and proved that there were no significant difference in the accuracy and precision between the results.