Abstract

A colour indicator-based assay was developed and validated for the quantitative analysis of Lisinopril in tablet in aqueous medium. The proposed procedure involved a reaction between the acidic functional group (COOH) of Lisinopril drug and standardised aqueous sodium hydroxide. The method involved dissolution of powdered Lisinopril tablet in water followed by filtering; the obtained filtrate was titrated with aqueous sodium hydroxide, and the end point was determined using phenolphthalein as indicator. The method which was applicable over a concentration range of 0.2 to 1.12 mg/ml gave an inter-day percentage of relative standard deviation (%RSD) of 0.11 to 1.67, while that of intra-day was 0.27 to 1.72 across the different concentrations used for the determinations. Similarly, the percentage of relative error (%RE) were 0.38 to 2.58 and 0.38 to 2.60 for the inter-day and intra-day assays, respectively. This indicates good accuracy and precision for the method. Furthermore, water soluble excipients did not interfere with the end point determination. Slight modification of the method involving potentiometrically determining the end point using glass calomel electrode system gave similar results. The application of both methods; potentiometry and phenolphthalein indicator-based to the chemical content assay of nine different brands of Lisinopril tablets showed no statistically significant difference between the two methods.

Key words: Lisinopril, phenolphthalein-based assay, titrimetry, potentiometry.