الفهرس 
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Abstract
New two simple and accurate spectrophotometric methods have been developed for the determination of some antihypertension drugs; enalapril maleate (ENP), prendopril (PRD) or and ramipril (RAM) in pure forms and pharmaceutical formulations. The first method is based on the formation of yellow colored ion-pair complex between the basic nitrogen of the drugs (ENP, PRD, or RAM) and acid dyes, namely; bromocresol purple (BCP) and bromophenol blue (BPB) in acidic buffer of pH range (2.8-3.0). The ion-pair complexes of ENP with BCP and BPB show maximum absorbances at 408 and 414 nm, respectively. The ion-pair complexes of PRD with BCP and BPB show maximum absorbances at 407 and 415 nm, respectively. The ion-pair complexes of RAM with BCP and BPB, show maximum absorbances at 409 and 413 nm, respectively . Beer’s law was obeyed in the range 2.0–28, 2.0-50 and 2.0-28 µg mL−1, for ENP, PRD and RAM, respectively with correlation coefficient ≥ 0.9991. In the second method, we investigate the development of indirect redox spectrophotometric reaction for the determination antihypertension drugs; enalapril maleate (ENP), prendopril (PRD) or and ramipril (RAM) with N-bromosuccinimide (NBS) in acid medium, followed by the determination of unreacted NBS by reacting it with a fixed amount of indigocarmine and measuring the absorbance at 610 nm (method A); amaranth and measuring the absorbance at 510 nm (method B) or methylene blue and measuring the absorbance at 663 nm (method C). In the three methods, the amount of NBS reacted corresponds to the amount of drug , the measured absorbance increase linearly with the concentration of the drug with correlation coefficients of 0.9993- 0.9998. Beer’s law is obeyed in the concentration ranges 0.1-3.4, 0.2-5.0 and 0.1-4.8 μg mL-1for ENP, PRD and RAM, 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 proposed methods were successfully applied to determine the studied drugs in their formulations without any evidence for interference from pharmaceutical additives and the results were statistically compared with those of the reference methods by applying Student’s t-test and F-test. The accuracy of the methods was further ascertained by performing recovery studies via standard-addition method. The proposed methods can be confidently applied for quality control and routine analysis of the studied drugs.