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Two spectrophotometric methods are described and applied to resolve ternary mixtures of the corticosteroid hydrocortisone (HYD) and the antibiotics nystatin (NYS) and oxytetracycline (OXY). The simultaneous determination of these three compounds was firstly accomplished by a derivative method using the “ratio spectrum-zero crossing derivative” and then by multivariate methods partial least squares (PLS)-1, -2 and principal component regression (PCR). Multivariate calibration methods provide, specially PLS-2 in this case, a clear example of the high resolving powder of these techniques. The two described procedures do not require any separation step. Repeatability and reproducibility studies were achieved over two series of 10 standards for each compound showing no significant differences at 95% confidence level in the four spectrophotometric methods. A comparison of the derivative and multivariate calibration results obtained in pharmaceutical formulations was performed resulting in agreement of the values obtained and the results was confirm by a high-pressure liquid chromatography (HPLC) method. [Copyright &y& Elsevier]

Five spectrophotometric methods are described and applied to resolve binary mixtures of the corticosteroid Dexamethasone and the antibiotic Polymyxin B. The simultaneous determination of the two compounds was firstly accomplished by two derivative methods using the "first derivative" and the "ratio spectrum-zero crossing derivative", which were satisfactory used to determine synthetic mixtures of these compounds in different ratios. Absorption spectra of compounds were used to optimise the spectral data set by performing the calibration by partial least squares-1 and 2 and principal component regression algorithms. These calibration models were evaluated by internal validation (prediction of compounds in its own designed training set of calibration), by cross-validation (obtaining statistical parameters that show the efficiency for a calibration fit model) and by external validation over synthetic mixtures. The five described procedures do not require any separation step. Repeatability and reproducibility studies were achieved over two series of ten standards for 9 and Polymyxin B showing no significant differences at 95% confidence level in the four spectrophotometric methods. A comparison of the derivative and multivariate calibration results obtained on synthetic mixtures was performed resulting in agreement of the values obtained. [ABSTRACT FROM AUTHOR]