The use of IR spectroscopy and density functional theory for estimating the relative concentration of triglycerides of oleic and linoleic acids in a mixture of olive and sunflower seed oils

Infrared spectra of five samples of sunflower seed oil and five samples of cold-pressed olive oil of different brands are recorded in the range of 650–3800 сm$^{-1}$. The structural models of eight fatty acids (oleic, linoleic, palmitic, stearic, $\alpha$-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic), as well as of triglycerides of the first four of these acids, are constructed using B3LYP/6-31G(d) methods. The vibrational wavenumbers and intensities in the IR spectra are calculated. The IR spectra of olive and sunflower seed oils are simulated using the supermolecular approach. The dependence of the intensity of vibrational bands at $\nu_{\operatorname{exp}}$ = 914 and 3009 сm$^{-1}$ on the concentration of triglycerides of oleic and linoleic acids in oils, as well as on the saturation degree of fatty acids, are studied. Experimental and empirical dependences are plotted to estimate the relative concentrations of triglycerides of oleic and linoleic acids in mixtures of olive and sunflower seed oils. The applicability of the density functional theory in combination with IR spectroscopy for characterization of vegetable oils is discussed.