Fig. 12

a Ratio spectra of 4 binary mixtures of DRO and CAF in different concentrations using the sum of normalized spectra of DRO and CAF as double divisor showing the obtained constant regions. b Ratio spectra of binary mixture of DRO and CAF (solid line), PCT (dotted line), PAP (dashed single dotted line) and their quaternary mixture (dashed double dotted line), 5 μg/mL each using the sum of normalized spectra of CAF and PAP as double divisor