Switch on fluorescence probe for the selective determination of lisinopril in pharmaceutical formulations: application to content uniformity testing.

Lisinopril, an ACE inhibitor, was selectively determined in pharmaceutical products using spectrofluorimetry. The method was based on the switch on fluorescamine fluorescence as a result of its interaction with the primary amino group of the drug in the presence of aqueous borate buffer (pH 9.5). The fluorescence emission was measured at 475 nm after excitation at 390 nm. The fluorescent product was suggested to be a diaryl pyrrolone cation which has a coplanar structure. Different experimental conditions affecting the reaction were optimized to give the maximum sensitivity. The fluorescence intensity was linear with the drug concentration in the range of 0.55-4.5 μg mL. The method was validated according to ICH guidelines and the result was acceptable. The calculated limits of detection and quantitation were 0.182 and 0.55 μg mL, respectively. The commercially available dosage forms containing lisinopril alone or in combination with hydrochlorothiazide were effectively analyzed by the proposed method. The obtained results were in agreement with those of the reported method in respect to accuracy and precession. Moreover, the suggested method was employed to determine the content uniformity testing of the investigated dosage forms.