Multi-component kinetic-spectrophotometric analysis. Selection of wavelength and time ranges

An empirical method for the selection of the best wavelength and time ranges which can be used in the quantification of binary mixtures, in a kinetic-spectrophotometric system, is proposed. It is based on finding those ranges which provide the least correlation between the kinetic profiles and the spectra of the products of reaction. The method was applied to the analysis of binary mixtures using simulated data with different rate constant ratios and in the presence of an interference that shows spectral overlap with the analytes. Subsequently, the proposed method was applied to the resolution of dyphylline and proxyphylline mixtures. The system studied was characterized by an elevated similarity in the kinetic behavior of the analytes under pseudo-first-order conditions and an elevated degree of spectral overlap of the products of reaction. In spite of this, satisfactory results were obtained in the quantification of the two analytes. The standard error of prediction (SEP) and the standard deviation between replicates (SDBR) did not show significant differences, being of the order of 4 and of 3% for dyphylline and proxyphylline, respectively.