Influence of the selected wavelength range on the simultaneous spectrophotometric determination of mixture components by use of partial least-squaresregression

This paper shows the benefits of optimizing the wavelength range and number of factors used in the simultaneous spectrophotometric determination of se veral analytes in the same sample by use of partial least-squares regressio n. The optimization criterion used for this purpose is based on the relativ e standard error of prediction (RSEP), which represents the overall error f or a series of mixtures containing different amounts of the analytes; the o ptimum wavelength range and number of factors are chosen to be those leadin g to the lowest RSEP value. The ensuing method was applied to the simultane ous determination of the diuretics spironolactone and althiazide at concent rations between 2 and 20 mg.mL(-1) in synthetic samples, where the drugs we re quantified with errors less than 5% (spironolactone) and 2.5% (althiazid e), and relative standard deviations below 3.5 and 0.8%, respectively. Both drugs were also determined in a pharmaceutical preparation, with recoverie s of 100.76% (spironolactone) and 95.86% (althiazide) relative to their nom inal contents, and relative standard deviations of 1.1 and 3.5%, respective ly. The proposed method for the analysis of the pharmaceutical preparation was validated by HPLC.