Spectrophotometric determination of ACE inhibitor drugs through ion-pair formation

ABSTRACT

Two simple and sensitive spectrophotometric methods were described for the determination of some angiotensin converting enzyme inhibitor drugs [ACE] such as Enalapril maleate [I], Perindopril [II], and Moexipril [Ill]. The two methods involved the formation of ion-pair reactions. The first method was based on the interaction of the cited drugs with bromothymol blue [BTB] at pH 2.5 followed by extraction by methylene chloride which absorbed at 404 nm for I, III and 415 nm for II. The second method was based on the reaction of molybdenum [V]-thiocyanate with the drugs followed by extraction of the complexes formed by methylene chloride which absorbed at 468 nm. The optimum conditions for the ion-pairs formation were established. Beer's law was obeyed for the first method over concentration ranges of 10-48, 4-40 and 5-45 micro g ml[-1] for I, II and III; while for the second method, it was obeyed over concentration ranges of 10-80 micro gml [-1] for l and II and 1-60 micro gm[-1] for III, respectively. The relative standard deviation calculated for Beer's law concentrations, were found to be less than +/- 1% for both methods. The limits of detection [LOD] calculated from the calibration curves in the first method were 0.4, 0.1 and 0.3 micro gm[-1] for I, II and III; respectively; whereas in the second method were 0.18, 0.2 and 0.35 micro gml[-1] for I, II and III, respectively. The two methods could be applied successfully for the determination of the three drugs in tablets, with no evidence of interference from excipients