From abstract: "The formation constants of the RChOH- species, formed by interaction of individual rare-earth nitrilotriacetate species and KOH at 25°C and an ionic strength of 0.1, have been determined by the potentiometric method, i.e., computed from the pH values of equilibrium mixtures containing varying proportions of rare-earth complex and base. The relationship of these constants to the ion-exchange separation of rare earths at high pH has been discussed."