Simultaneous separation of yttrium and lanthanide ions by isotachophoresis

An operational electrolyte system was developed for the isotachophoretic separation of fifteen rare-earth elements (yttrium and lanthanides except for Pm) by adding a helping complexing agent to an alpha-hydroxyisobutyric acid (HIBA) electrolyte system. As a result of testing several helping agents such as malonic acid, malic acid, tartronic acid and glycolic acid, the optimized leading electrolyte was a 20-mM ammonia solution containing 2 mM malonic acid and 7.5 mM HIBA (pH 4.8, 2-ethylbutyric acid buffer). The terminator was a 20-mM carnitine hydrochloride. According to the stability constants of rare-earth-malonate complexes evaluated by isotachophoretic method, the successful separation was due to the smaller stability constants of Y-malonate complexes compared with those of the medium lanthanide elements to be separated.