Colorimetric microdetermination of enalapril maleate in pharmaceuticals and spiked biological fluids using redox reactions

ABSTRACT

Five simple, sensitive, rapid, and reproducible procedures [A-E] for microdetermination of enalapril maleate in pharmaceuticals and biological fluids are investigated. Procedures A and B are based on oxidation of enalapril maleate by Fe[3+] in the presence of bipyridyl [bipy] or o-phenanthroline [o-phen]. The formations of tris-complex upon the reaction with Fe[3+]-bipy and/or Fe[3+]-o-phen mixture in optimum conditions were demonstrated. Procedure C is based on the oxidation of enalapril by N-bromosuccinimide [NBS] and determination of the unreacted NBS by measuring the decrease in absorbance of amaranth dye [AM] at 520 nm. Procedures D and E include the addition of excess Ce[4+] and the determination of the unreacted oxidant by the decrease of the red color of chromotrope 2R [C2R] at 527 nm for method D or the decrease of the orange pink color of rhodamine 60 [R6G] at 524 nm for method E. Regression analysis of Beer's plots showed good correlation iii the concentration ranges 0.2-5.75 micro g ml[-1], whereas optimum concentration ranges applying Ringbom method were 0.4-5.6 micro g ml[-1]. The apparent molar absorptivity, Sandell sensitivity, detection and quantification limits were calculated. The developed procedures were applied successfully for the determination of enalapril maleate without interference from common excipients in pharmaceuticals and biological fluids