Abstract
Photoacoustic (PA) spectral measurements in the visible region were made for methyl orange contained in physical mixtures with α- and β-cyclodextrins, ground mixtures, and the inclusion compounds.Inclusion of methyl orange in β-cyclodextrin (molar ratio 1: 1) was confirmed by the Bs type phase solubility diagram.The inclusion compounds of α- and β-cyclodextrins showed very similar PA patterns (λmax at 445nm) which were different from the pattern of the physical mixture (λmax at 395nm).The physical mixture showed a gradual change of its PA pattern to that of the inclusion type as a function of grinding time.The pattern of the ground mixture was broader than that of the inclusion compound, but became coincident with it after storage at 40°C and 96% relative humidity for 4d.
It was concluded that PA spectral measurement is an effective method to investigate inclusion phenomena in the solid state.
