Abstract

Four simple and sensitive procedures (methods A, B, C and D) for the assay of lisinopril in pure form and formulations are described. Methods A and B are based on the condensation of lisinopril (acyclic imino acid) with ninhydrin (indane-1,2,3-trione hydrate) in the presence of ascorbic acid (method A, λmax 560 nm) or ascorbic acid (method B, λmax 520 nm). Method C is based on the initial , formation of water insoluble adduct involving lisinopril and phosphomolybdic acid, followed by release of phosphomolybdic acid from the adduct with acetone and color development with cobalt nitrate-ethylenediaminetetraacetic acid disodium salt complex (λmax 840 nm). Method D is based on the formation of colored radical anion on treating lisinopril with 2,3-dichloro,5,6-dicyanol, 4-benzoquinone (λmax 4 60 nm). The variable parameters in all these methods have been optimized. The results were statistically validated.