New pH-Metric method for determination of some angiotensin converting enzyme inhibitors through their complex formation with some transition metal ions

Study of mixed ligand complexes of Co[2+] and Zn[2+] with three Angiotensin converting enzyme inhibitors [ACE] was conducted in aqueous solution by pH metric titration. These are Enalapril maleate [I], Perindopril [II] and Moexipril [III] and one of the amino acid family [glycine]. Protonation constants of the three drugs and stability constants of the binary and ternary complexes were determined at [25 +/- 1] [degree sign] C and ionic strength 0.1M NaCl. The stability constants of the binary complexes of I, II and III with Co[2+] and Zn[2+] were performed and the results indicate the presence of one formation constant for the complexes of Co[2+] and Zn[2+] ions with II and III and two formation constants for I. By introducing glycine in the above binary complexes, ternary complexes were formed. The formation constant of the ternary complexes of I, II and III with Co[2+] and Zn[2+] ions with glycine was also calculated at the same temperature and ionic strength. This potentiometric technique was utilized also for the determination of the cited drugs

Spectrophotometric determination of ACE inhibitor drugs through ion-pair formation

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