Fig. 11

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