Kinetic spectrophotometric resolution of binary mixtures using three-way partial least squares

Three-way partial least squares (PLS) was applied to kinetic—spectrophotometric data. The coupling reaction of diazotized sulfanilamide with o-, m- and p-amino benzoic acid (ABA), and with orciprenaline (ORC), to give azodyes was monitored. Three binary mixtures of substrates, i.e., o-ABA/ORC, m-ABA/p-ABA and o-ABA/m-ABA, with different values of the rate constant ratio and spectra which overlapped seriously were studied. The spectra of the mixtures were scanned with a 2 nm resolution every 30 s during ca. 15 min. The data sets contained from 30 × 36 to 30 × 48 time—wavelength data. Nine mixtures of each binary combination of substrates were used for calibration, thus the three-way calibration data sets contained from 9 × 30 × 36 to 9 × 30 × 48 concentration—time—wavelength data. The two-way PLS modelling was constructed on the basis of single wavelength kinetic curves, and the three-way PLS modelling was applied to series of three-way data arrays consisting of a number of selected wavelengths each (up to the whole spectra). The results based on three-way data arrays were better than that of ordinary PLS, particularly with mixtures having both a low rate constant ratio and small spectral differences.