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.
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