Comparative study of the ratio spectra derivative spectrophotometry, derivative spectrophotometry and Vierordt's method applied to the analysis of lisinopril and hydrochlorthiazide in tablets

Three new spectrophotometric methods are described for the determination of lisinopril and hydrochlorthiazide in their binary mixture: First derivative spectrophotometry,ratio spectra derivative and Vierordt's method. The procedures do not require any prior separation. In the derivative spectrophotometry, the dAld lambda values in the first derivative spectra of the mixture were measured at 289.6 nm for lisinopril and at 279.8 nm for hydrochlorthiazide. The calibration graphs were linear in the range 25.56-129.50 mu g.ml(-1) for lisinopril and 10.60-139.50 mu g.ml(-1) for hydrochlorothiazide. In ratio spectra derivative spectrophotometry, the calibration graphs for 15.88-129.50 mu g.ml(-1) lisinopril and for 5.98-139.80 mu g.ml(-1) hydrochlorothiazide were obtained by measuring the signals at 253.7 nm and 243.6 nm for lisinopril and at 280.1 nm and 270.8 nm for hydrochlorothiazide. In Vierordt's method, A(1)(1) (1%, 1 cm) values of lisinopril and hydrochlorthiazide were determined at 259.8 nm and 272.7 nm in the zero - order spectra. The quantity of both compounds were calculated by using the A(1)(1) (1%, 1 cm) values. The methods were successfully applied to a pharmaceutical formulation for determination of both active compounds.