Spectrophotometric determination of lisinopril in tablets using 1-fluoro-2,4-dinitrobenzene reagent

A spectrophotometric method for the determination of lisinopril (LN) in single and multicomponent tablets also containing hydrochlorothiazide (HCT), based on the derivatization reaction with 1-fluoro-2,4-dinitrobenzene (FDNB, Sanger reagent) is described. Aqueous solutions of LN (4.5-27.2 x 10(-5) M) react with FDNB (in acetonitrile) at pH 8.2 (borate buffer) in dark at 60 degrees C for 45 min. After acidification with HCl to decolourize 2,4-dinitrophenolate (the alkaline hydrolysis product of FDNB), the LN-derivative is measured at 356.5 or 405.5 nm (only at 405.5 nm if HCT is present). The calibration curves are linear (r>0.996 at both wavelengths) with a between days precision of slopes of 1.8 and 2.3% at 405.5 and 356.5 nm, respectively. The quantification limit is 3.49 x 10(-5) M (0.014 mg) at 405.5 nm and 5.69 x 10(-5) M (0.023 mg) at 356.5 nm. The accuracy and precision of the method were evaluated with the analysis of synthetic mixtures (Er%: 0.30-0.60 and 0.27-1.00 at 405.5 and 356.5 nm, respectively; RSD%: 0.48-0.92 and 0.35-0.51 at 405.5 and 356.5 nm, correspondingly; recovery%: 99.2-100.4 at 405.5 nm and 97.9-104.3 at 356.5 nm). Results obtained from the analysis of commercial preparations with the proposed method are in good agreement with those obtained with the official HPLC method (% relative difference 0.2-2.5%). The developed method can be used for rapid routine analysis for content uniformity, dissolution profile studies and assay of pharmaceutical preparations.