Spectrophotometric and HPTLC-densitometric determination of lisinopril and hydrochlorothiazide in binary mixtures

Different spectrophotometric and HPTLC-densitometric methods are presented for the simultaneous determination of lisinopril and hydrochlorothiazide in pharmaceutical tablets. The spectrophotometric methods include third derivative (³D) ultraviolet spectrophotometry with zero crossing measurement at 217.4 and 233.4 nm, second derivative of the ratio spectra with measurement at 214.3 and 228.0 nm; both classical least squares and principal component regression were applied to the UV absorption and first derivative spectra of the mixture. The HPTLC method was based on separation of both drugs followed by densitometric measurements of their spots at 210 and 275 nm for lisinopril and hydrochlorothiazide, respectively. The separation was carried out on Merck HPTLC aluminum plates of silica gel 60 F₂₅₄, using chloroform–ethylacetate–acetic acid (10:3:2 by vol.) as mobile phase. The linear and second order polynomial were used for the regression equation of lisinopril and hydrochlorothiazide, respectively.