A new method for measuring the solubility of slightly soluble substances in supercritical carbon dioxide

Abstract

A self-consistent approach to the measurement of the solubility of biologically active compounds in supercritical (SC) media based on infrared spectroscopy is exemplified by paracetamol in supercritical CO₂. According to this approach, the integral extinction coefficient for a chosen analytical spectral band is determined from additional spectroscopic measurement of the compound under study dissolved in an inert solvent at known concentrations in the considered range of the parameters of state (pressure and temperature, p and T). The values of solubility of the compound under study in the SC medium are calculated based on the above-obtained values of the extinction coefficient and the analytical values of the integral intensity of the chosen spectral band for saturated solutions in the p,T-range of interest. The method allows one to determine the solubility with a high accuracy even if the measured values are as low as 10^–4–10^–1 mol %.