Application of Chemometrics Approaches to Analysis of Mid-Infrared Spectra of Ibuprofen Diluted in Supercritical Carbon Dioxide

This work represents a comprehensive analysis of mid-infrared (mid-IR) spectra of ibuprofen diluted in supercritical CO₂ (in the temperature range of 40–90 ℃ and at the CO₂ density corresponding to 1.3 of its critical value). The study employed mathematical approaches based on data matrix analysis such as two-dimensional cross-correlation analysis (2D-COS) and principal component analysis (PCA). Two-dimensional cross-correlation analysis allowed us to reveal correlations between the spectral contributions constituting the analytical spectral band and assigned to certain ibuprofen conformers, as well as the significance of these correlations. It has been shown that the considerable increase in the total intensity of the analytical spectral band, proportional to the equilibrium ibuprofen concentration in the supercritical CO₂ phase, is accompanied by certain redistribution of intensities of the spectral components related to the corresponding conformers. The PCA allowed us to determine the changes of intensities of individual spectral contributions for each thermodynamic point in the considered temperature range. It has been shown that these two complementary methods provide more precise information that may be used as the initial data in the classical analysis of spectral data based on spectral curve deconvolution into individual spectral contributions.