A simplified method of the calculation of the partition function (β-factor) based on the application of the algebraic expressions for the isotopic increments of the FG-matrice Spur of secular equations has been developed. By means of the above and the other methods β-factors of complex compounds with mono- and polyatomic ligands including chelates were calculated, β-factors were found to be calculated according to additive rule from β-factors of isostructural complexes with identical ligands. The probability of the appearance of different meanings of the separation factors for isotope exchange reactions of different classes has been investigated. It was found the equilibrium isotope effects of complex compounds are greatly dependend on the difference of valence states of the element, coordination numbers and ligand type.