SIMULTANEOUS RESOLUTION OF DEXAMETHASONE AND POLYMYXIN B BY SPECTROPHOTOMETRY DERIVATIVE AND MULTIVARIATE METHODS

Abstract

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 Dexamethasone 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.

Keywords:

• Corticosteroids
• Derivative spectrophotometry
• Partial least squares
• Partial component regression
• Dexamethasone
• Polymuyxin B

ACKNOWLEDGMENTS

We wish to thank the DGES of the Ministerio de Educación y Ciencia for the financial support (Project PB-97-0431).