The article presents the results related to the study of distribution of biologically active substances from the plant raw material between solid and liquid phases. The aim of this study is to develop theoretical bases of the extraction process in the equilibrium state by the example of study and modeling of the distribution process of biologically active substances from Eucalyptus viminalis leaves. In these studies, we used ground plant raw material of E. viminalis leaves with particle fraction of 0.1-0.5 mm; and ethanol with concentration 80% ±1% v/v was used as an extractant. Qualitative and quantitative analyses were carried out by reversed phase high-performance liquid chromatography with rutin, chlorogenic acid, and euglobal standards equivalent to spissum extract of chlorophyllipt of the State Pharmacopoeia of Ukraine. A hypothesis has been suggested that Henry's adsorption law and the law of conservation of matter play a fundamental role in this process. The experimental data are described well by the suggested equation with high value of determination coefficient R 2 =0.99. At the same time, F-test and the significance of coefficients in equations satisfy the statistic condition, which means that the current hypothesis about the adsorption mechanism of distribution of biologically active substances in the extraction system is not refuted. The results of these studies demonstrate good agreement of experimental data and theoretical model based on Henry's adsorption law and mass balance. The numerical values of constants in the model suggested have been calculated.
Keywords: Distribution; Eucalyptus viminalis Labill; equilibrium; leaves; phenolic compounds.