Spectrophotometric determination of lisinopril in pharmaceuticals using ninhydrin- a modified approach

An accurate and precise spectrophotometric method is presented for the determination of lisinopril based on the formation of a yellow colour product with ninhydrin in the presence of bicarbonate with an absorption maximum at 420 nm. The reaction proceeds quantitatively at 97±1℃ in 10 min. The calibration curve is linear over the range of 5.0-50.0μg/mL and is described by the regression equation A=(-)0.0175+0.0079 C with a regression coefficient (r) of 0.9979(n=6). The calculated molar absorptivity and Sandell sensitivity values are 2.02×10^3 L/mol/cm and 0.219μg/cm^2, respectively. The limits of detection (LOD) and quantification (LOQ) calculated as per ICH guidelines are 0.68 and 2.07μg/mL, respectively. The within-day accuracy expressed as relative error was better than 2.5% with precision (RSD) ranging from 1.02 to 1.93%. The between-day accuracy ranged from 1.5-3.0% with a precision less than 4%. The method was successfully applied to the analysis of three brands of tablets containing lisinopril. The results obtained were in agreement with those obtained by the BP method. Accuracy was also checked by placebo blank and synthetic mixture analyses besides a recovery study via standard addition procedure. The method was also used to check the stability of lisinopril in solution.