Abstract
Four simple titrimetric procedures are described for the determination of lisinopril (LNP) in bulk and in pharmaceuticals based on the neutralization of basic-amino and acidic carboxylic acid groups present in LNP. Method A is based on the neutralization of basic amino groups using perchloric acid as titrant in anhydrous acetic acid medium. Method B, method C and method D are based on neutralization of carboxylic acid group using NaOH, sodium methoxide and methanolic KOH, as titrants, respectively. Method A is applicable over 2.0-20.0 mg range and the calculations are based in the molar ratio of 1:2 (LNP:HClO4). Method B, method C and method D are applicable over 2.0-20.0 mg, 1.0-10.0 mg and 5.0-15.0 mg range, respectively, and their respective molar ratios are 1:1 (LNP:NaOH), 1:2 (LNP:CH3ONa) and 1:1 (LNP:KOH). Intraday and inter day accuracy and precision of the methods were evaluated and the results showed intra- and inter-day precision less than 2.7% (RSD), and accuracy of < 2.5% (RE). The developed methods were applied to determine LNP in tablets and the results were validated statistically by comparing the results with those of the reference method by applying the Student’s t-test and F-test.
Highlights
Lisinopril, 1-[6-Amino-2-(1-carboxy-3phenyl-propylamino)-hexanoyl]-pyrrolidine-2carboxylic acid, is a lysine derivative of enalaprilat, the active metabolit of enalapril. It is an angiotensin converting enzyme (ACE) inhibitor used in the treatment of hypertension, heart failure, acute myocardial infarction and preventing renal and retinal complications of diabetics [1] and was introduced into therapy in 1990s [2]
Certain successful attempts have been made for the determination of LNP in pharmaceuticals using different analytical techniques
A stock standard solution of LNP containing 2 mg/ml was prepared in glacial acetic acid, 2 mg/ml in water, 1 mg/ ml in 3:1 benzene:methanol and 1 mg/ ml in methanol
Summary
Lisinopril, 1-[6-Amino-2-(1-carboxy-3phenyl-propylamino)-hexanoyl]-pyrrolidine-2carboxylic acid, is a lysine derivative of enalaprilat, the active metabolit of enalapril. The official methods for the determination of LNP are potentiometric acid-base titration [2] and HPLC [3] using actylsilane column at 50 0C and phosphate solution-acetronitrile (96:4 v/v) as mobile phase. The present manuscript describes four sensitive titrimetric methods for the determination of LNP in both pure form and in tablet form. A 0.005M sodium methoxide (standardized against benzoic acid) was prepared in 3:1 benzene: methanol and 0.2% (w/v) phenolphthalein in same solvent for method C. A stock standard solution of LNP containing 2 mg/ml was prepared in glacial acetic acid (method A), 2 mg/ml in water (method B), 1 mg/ ml in 3:1 benzene:methanol (method C) and 1 mg/ ml in methanol (method D)
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