Development of a new solution for determining the solubility limit of quercetin and other poorly soluble substances in aqueous solutions using the method for determining total organic carbon

Aim. Given the incompleteness of literature data on the solubility of quercetin and the importance of this physicochemical characteristic in the study of its bioavailability, there is a need to develop an alternative method for accurately quantifying the solubility limit of quercetin. Materials and methods. The concentration of quercetin in the samples was determined by directly determining the total organic carbon. For measurements, a total organic carbon analyzer 450 TOC (METTLER TOLEDO) was used with a range of measured values of 0.05–1000 ppbC µgC/l. Results. The exact limit of the solubility of quercetin, as a poorly soluble substance, has been established. Having previously measured the value of total organic carbon in the prepared solutions, we obtained data on the concentration of quercetin in solutions depending on the pH of the solution. Having built a graphical dependence of the measured values of the concentration of a substance on the pH values of the studied solutions, we obtain a mathematical equation of the reliance. Using the resulting function equation, one can approximate the concentration value of a substance with a pH value of 7.0. This value will be the solubility limit of the test substance for neutral media. Conclusions. As a result of the research, a new method was proposed for the quantitative determination of the solubility limit of a substance, with an accuracy not exceeding 5.0 %. The method is based on measuring the concentration of total carbon in acidic solutions with different pH values and subsequent approximation of the obtained dependence of the pH value equal to 7.0