Abstract:
Simultaneous determination of quinapril (QA) and hydrochlorothiazide (HCT) in tablets were accomplished by ratio spectra first order derivative spectrophotometry (graphical method) and chemometric method (numerical method). Both methods do not require any chemical separation step. In the application of two analytical methods, the absorption spectra in the working range of 4.0-20.0 mu g/mL QA and 2.5-12.5 mu g/mL HCT were plotted in the wavelength range of 210-350 nm. In the graphical approach, the absorption spectra of QA and its binary mixtures in the selected spectral range of 210-280 nm were divided by the standard spectrum of 10 mu g/ mL HCT and their absorption spectra were obtained. In the similar way, the ratio spectra of HCT in the wavelength region of 210-350 nm were also obtained by using the standard spectrum of 12 mu g/mL QA. First derivative of the ratio spectra obtained in the above steps were calculated by Delta lambda=5 nm interval for both drugs. Calibration equation functions were obtained by measuring (he ratio spectra derivative amplitudes of the minima at 219.9 nm for QA and 283.2 nm for HCT in the above mentioned spectral ranges for each drug. In the numerical method, the critical wavelengths corresponding to maximum points at 213.0 nm for QA and 220.0 nm for HCT in the zero-order absorption spectra were selected to construct the least squares calibration (CLS). Both graphical and numerical methods developed in this study were completely validated and applied to the quantitative analysts of tablets containing QA and HCT The results obtained from the developed methods were compared with each other as well as to those obtained by classical derivative spectrophotometry, which have different experimental conditions than the previous derivative method, and the difference was not observed statistically significant.