Simultaneous determination of chlorthalidone and spironolactone with univariate and multivariate calibration: wavelength range selection.

Chlorthalidone and spironolactone were determined simultaneously with the aid of univariate and multivariate calibration methods. Univariate calibration was performed by the zero-crossing and derivative ratio spectrum methods. Extensive spectral overlap and the scarcity of wavelengths in derivative spectra allowing one analyte to be distinguished and quantitated in the presence of the other gave rise to poor results that called for multivariate calibration. Partial least-squares regression was used in combination with a suitable method for selecting the optimum wavelength range and number of factors for analysis. The ensuing method was applied to simultaneous determination of chlorthalidone and spironolactone in a commercially available pharmaceutical preparation. The results were validated by high-performance liquid chromatography.