Isosbestic points in absorption spectra of isooctane, n-heptane, toluene, and benzene binary mixtures

Experimental absorption spectra of several pure hydrocarbons such as isooctane, n-heptane, toluene, and benzene and their binary mixtures are compared in the 1090–1240 nm and 1620–1820 nm wavelength regions, in which the second and first overtones, respectively, of vibrational frequencies of molecular groups CH, CH2, and CH3 are located. It is shown that in all cases there exist narrow isosbestic areas for binary mixtures specific for each of them. These areas can serve as individual characteristics of binary hydrocarbon mixtures, making qualitative analysis possible without recording the entire spectrum. Optimal wavelengths for quantitative analysis of the hydrocarbon mixture composition are determined for which the dependence between the absorption coefficient and the component concentration is approximately linear.