Determination of the stability constants of lanthanide complexes with oxyacids using capillary electrophoresis

Different algorithms for calculating the stability constants of lanthanide complexes with hydroxycarbonic acids on the basis of experimental data obtained by capillary electrophoresis are compared. It is shown that the optimal approach is based on the consideration of the electrophoretic mobilities of all complex forms present in the solution, taking into account their fractions. The most satisfactory approximation of the experimental data by the calculated ones is achieved on the assumption that the electrophoretic mobilities of the complex species depend on their charge only, regardless of the particle size. The obtained stability constants of lanthanide complexes with lactic and 2-hydroxy-2-methylpropanoic acids agree with the literature data. The stability constants of lanthanide complexes with tartaric and citric acids were significantly corrected, while the constants for complexes with mandelic, 2-hydroxy-2-methylbutanoic, 2-hydroxy-2-propy-lpentanoic, and malic acid were determined for the first time.