The fallacy of using solvent extraction for the study of metal/ligand complexation in mixed solvent systems

Metal complexes can be identified by ion mobility mass spectrometry, often using mixed aqueous solvents, which improve the electrospray ionization process but induce significant changes in thermodynamic values associated with metals and ligands. This work demonstrates that the addition of 10% acetonitrile and 1.0% dimethyl sulfoxide leads to an increased autoprotolysis constant, does not influence the nitrilotriacetic acid -pKa values, but decreases europium extraction in a solvent extraction system. This work shows the inability to quantify the stability constant of Eu/NTA complex in mixed solvent using a solvent extraction technique, as polar solvents are dissolved in the dodecane organic phase.